If this guy doesn't teach electronics, he should. I am a retired Electrical Eng., and this was the most basic (yet informative) explanation I've ever heard. Anyone watching it, and then not having a good understanding of " Turns Ratio ", was either not paying attention, or needs to find another hobby.... Jim
So that green/white wire hanging under my transformer is a center tap! I never found a schematic for this amp (1956 Ampeg GuitarAmp , according to the serial number). The wire was coiled in a corner unconnected to anything. I connect that to GND thinking it might be a transformer case ground and the amp lost a good amount of its background hum. The rest of the hum disappeared when I ran two 100 ohm resistors from the 6vac filament lines to ground. What a difference! It is a pleasure to play on this amp....so quiet. Thank you for all the great practical information.
I actually did this on a Milbert car tube amp to verify the output transformers are the same as the old Berning EA-230 schematic (6.5K). I read the info online but your video was more "real" and very helpful. Thanks!
Thank you very much for posting this. Us younger guys feeling our way through the dark with this appreciate all you more experienced guys, your knowledge, and your sharing this with us!
This is a great way to both to check a transformer for ratings AND to check if the transformer is blown. Thank you for sharing your knowledge and experience. This was extremely helpful!! Gratitude.
Thanks David. I'm looking at some of your older videos. Good stuff here. 1) I like the fact you twist your wires. I do this with all my wiring except the blue and brown wires on OTs typically used for plate connections on tubes. I think these two should be separated. 2) it's the same safety consideration with soldering. I have burned myself too many times to count. It was usually when I was distracted and not paying strict attention. I had to educate my other half to not disturb me when soldering :-) Also, if your soldering iron slips out of your hand for any reason and lands on a component, that component may be destroyed. I know from experience. Easy to understand explanations in this video. Good job.
No truer words when working on HV. I was bit by an operating microwave transformer, 2,400V 1000 watts when my shop assistant was yapping in my ear rather than doing his own work. The only reason I am alive is because I followed rule #1, keep 1 hand in your pocket, and wear insulated shoes. It hurt like a son of a bitc- and threw me about 6 feet. The second time I was walloped by the 2nd anode of an operating picture tube because the same assistant didn't clean off the glass, and 2nd anode cup before attaching it. Debris on the glass set up the perfect storm for a bolt of lightning to do a number on my hand, and split my thumb nail in 2. That one felt like hitting my thumb with a hammer. Needless to say my shop assistant was flipping burgers after that. I actually enjoyed firing his ass.
@@radiojet1429 You know when a soldier says he re-lives battles, and firefighters say they re-live fires or bad accident scenes, and police officers re-live horrible crime scenes. PTSD is real. For years I would have vivid dreams of grabbing a live wire and not being able to let go. One time I threw my arm out trying to break the current and hit the wife who was sound asleep. She wasn't happy.
Some people think they know ...........YOU SIR are well......... unreal........I truly love your videos and before you I did not think I would ever grasp all this craziness.... I am starting too and I sure appreciate it. If you ever build another kilowatt or whatever huge amp, love too document what it sounds like with a guitar through it. I have guitars and will travel. I love ya brother. I would love too be the first man too play guitar through one of those crazy amps.......I think it would make a lot of noise in the guitar world...get it........Thanks so much.......
One of the challenges of building efficient class B audio vacuum tube amplifiers is the fact that the output impedance of the tubes varies with conductance, which varies with screen grid voltage and control grid voltage. It's one of the things that creates nonlinearity in tube amplifiers. Making matters more challenging, imagine you're using MOSFETs to control screen voltage dynamically to respond to program peaks while keeping screen voltage low at idle, so the idle power is low. In reality, high fidelity and efficiency lie on opposite ends of the spectrum. It takes clever engineering to cancel out many of these distortion inducing technologies to make an amplifier that is both efficient and high fidelity.
Great video. I just did this on a used transformer I recently picked up to test. I don't have a variac, so I put a light bulb socket in series with the power transformer and ran the output off the 6.3 filament taps. Worked perfectly.
I think it is worthy of mention that because Impedance is the term used for alternating current as opposed to Resistance for Direct Current and both exist on the primary o an Output Transformer and because the impedance of speakers is dynamic - varies with frequency - the actual dynamic impedance of the load on the Primary and therefore on the Plates, varies as well. Also if you notice that the "required" P to P load impedance of a given tube changes with both DC voltage and Class of Operation (Class A needs a higher load Impedance than Class AB or Class B) and what this translates to is the linearity of frequency response under those dynamic conditions, it can be seen that it is safe to use a higher impedance speaker than was originally designed for, especially if you wish to increase supply voltage different than the example in the book or if you'd like to try a different Class of Operation. For example it has long been noted than guitar amplifiers in which some kinds of distortion (non-linear response) are desirable can often benefit by plugging for example an 8 Ohm speaker into the 4 Ohm Jack/Secondary winding. It will likely be necessary to adjust the bias voltage to get the best sound or to get to Class A responsiveness but if you don't go overboard and/or monitor current conditions while playing, you can discover new tonality and distortion characteristics in your amp. YMMV but this is one advantage of Vacuum Tube amps which require Output Transformers as opposed to Solid State most designs of which eliminate the Output Transformer. Output Transformers are one reason Tube amps sound different from Solid State amps... not the main reason, but one reason.
The impedance changes with the frequency. I own a digital diplay LCR bridge and a variable AC power supply. The power supply reflects a load from 1 Ohms to 1000 Ohms, @ 1-1000Hz. The bridge will send AC signals from 1Hz up to 100KHz. Some of the audio transformers are impedance rated for ____ Ohms at 100 Hz, 400 Hz, 600Hz (600Hz is the old telephone company standard) or 1000 Hz. A non-inductive DC resistance load is not at all the same as a reactive inductive/capacitive speaker load. That load changes with the frequency. An 8 Ohm speaker can swing from 3 or 4 Ohms up to 13 or 14 Ohms IMPEDANCE.
Ty, really appreciate your advice - Thank You. The short of it is 1) 30% of my house electrical system has not been updated, and 2) to save on the electrical bill we have all curly Q florescent light bulbs which REALLY DOES save us considerable money. I know both those situations cause havoc on guitars and amps. STORY HAS A NICE ENDING THOUGH - My friend loved the guitar and asked me to sell it to him. I told him to check it out at his house on his amp first to make sure everything was OK, and it was...
those lights are terrible for your eyes...all 'blue spectrum' no reds or orange....they also disrupt your circadian rhythm., making you not sleep.... i loved them at first....they are cheap and REALLY bright....but then i started having problems, detached retinas, stuff like that.....the old incandescent bulbs are SO much better for you.
Very informative video! Thanks a lot! It seems I'm not the only one who see similar interesting stuff here and at Uncle Doug's. I'm glad I found both of you! :)
I have three of these beauties now. One measures up to 6KV and the other 5 KV. I "smoked" one not too long ago by measuring an audio voltage out of a modulation transformer that was a bit over 2000 volts AC but it was at 1 KHz. That was a bad idea. It arced the switch and I was finally able to find it and scratch the carbon of with dental tools. I kept a paper schematic inside the meter and it almost caught it on fire. It works proper again now but I don't use it any longer for HV measurements. High voltage at virtually any audio frequency will arc much further than 60 Hz and I knew that but thought it wouldn't happen.
Awesome video and great explanations on how to measure unknown transformers. And for sure you never can warn people enough about the dangers of high voltage! But there was a little mistake with looking up the numbers on the single ended one. You were looking up plate resistance in the book which is not the right value. It must be load resistance. And you were looking up the 6AQ5 in triode connection which needs a different value as well. Plate resistance for the 6AQ5 at 250V Class A is appr. 52kOhms while load resistance is about 5kOhms. For a 6BQ5 or EL84 load resistance is typically 5,2kOhms while with different Bias settings you can also use 4.5kOhms or 7kOhms. So in the end it will fit for both tubes at 8 Ohms secondary.
+Pentode3000 I have to agree with you. Looking in the tube manual again, I see I looked at the plate resistance instead of the load resistance. I do appreciate you pointing it out and I hope others see this correction. If I can figure out how to insert an information bubble in the video I will make this correction.
Thanks so much for this information on Transformers I think this will really help me in that I consider myself to still be a novice at building repairing and troubleshooting tube amps but I really love this hobby I love music and I think this is truly going to help me. Right now I am working on a silvertone tube amp that came out of an organ from probably the mid to early 60s, I have two of these amplifiers that are identical and they use 6 B Q V output tubes two of them in the output but all the connections are made on the side of the amplifier through a plastic block that couples with another one and of course I don't have a schematic for this amplifier and I'm trying to locate one now but I'm also trying to figure out where the speaker leads would connect and also the volume and tone connections as well. I think this will give me a good idea of what is what and I'm going to try to sort it out from there, thanks so much for the video, great job.
For 08:48, this is a beauty! It is for driving transmitting tubes with grid current:) :) The easiest way to get some serious power out of them is use AB2 with grid current is an interstage transformer....With the grid center tap goes to the bias voltage, or may be ground if you going to power up some 1k or more plate dissipation tube-beasts;)
At around 1:15, you described the configuration with a cap to ground on either side of the choke as a choke input filter. I know you know the difference and that it was a slip, but for those that don’t, it is a capacitor input Pi filter.
Thank you... this is important as mistakes can confuse a new-comer. TH-cam took away the ability to add speech-bubbles a few years back as they do not show up on remove viewing devices like iPhones/smartphones, etc (only computers) and apparently that is what most videos are watched on, so now when we make an error in our posting, we can't add that speech-bubble and correct it.
I built a project ecc83 and 2 el84 amp from an old philips mains transformer the design came from online very low component count but i was too poor to buy output transformers i had 2 matching 230v mains transformers laying around Big ones and worked out if i could use them size of them was overkill for 2x5 watts but the secondary windings worked out perfect for 8 ohms or 4 ohms as it had a centre tap on the secondary I fired it up and it sounded great powerful too considering i used my TDL rtl3 speakers that are no so efficient But then i read that good se transformers have air gaps something to do with the magnetic flux in the core of the transformer. so i looked up how to do that.its air gaps between the E and I metal plates.So i took all the Es and Is out and stuck thin strong sort of stiff cardboard on all and then packed them all back in.And the result was mind blowing.since then 20 years ago i have owned a lot of high end equipment.I love class a so expensive equipment. But i have never heard since the quality of the little amp i made myself.playing a beatles CD you can always hear the difference between john and paul .but with my home made amp the difference was much more like they were singing right in front of you.
I understand what you mean. Some of the amplifiers I have built that I like the most usually do not test out to be perfect on the bench. A perfect example of that is a SET amplifier. THD is always higher than any decent push-pull amplifier but the SET may have a "magical" sound to it the PP amplifier does not have. I have plenty of high-end equipment but I listen to my homebrew 7591 stereo amplifier using the UTC output transformers. For reasons I can not exactly explain, I prefer it over my McIntosh tube amps. Thanks for your thoughts and comments.
I really appreciate this kind of video... dum dums like me can understand. a lot of videos on youtube that guy is just talking over everybody else's head. but this.. this is my pace.
Thank you. I just spent a couple hours looking this up. Reading everything you explained here. I did all the math per what I read and wasn't sure if I did it right....Then I find this video and confirmed it. I have a few more OT's I can go figure out now. Thanks again.
very good and informative explanation here ,so good I had to subscribe to your channel ,im a 1st timer but it def wont be the last time ,thanks for your great teaching knowledge uncle doug is a great teacher as well ,between the 2 of you im learning alot ,I have had electrical therory being a commercial electrician ,and your right you dont want any distractions when working with high voltage can def relate to that ,i have installed breakers in 480 volt panels before that couldnt be turned off and you dont want anything or anyone around you
You can use Power Transformer as an output transformer as long a you do not overdrive the magnetic field. I used center tapped (good to have 230V AC mains, i can use 120V two winding or centertapped transfomers) or two times winded Mains transformers a lot to test some pushpull amplifiers without the need of an expensive OPT in the first place;) But this is for experienced "tubetinkers" only;)
Did any of this come out of Friendship-7? I did not belive about putting my hand in pocket until one day I put both hands on my amp...Keep up the Lessons. Thanks so much...
I had a nice collection of transformers out in California. I had a reasonably good job and a house too. Then the economy turned just enough that I wasn't able to sustain my house. Then I found myself living in an equipment yard in a box truck battling all manner of thieves, tweakers, recyclers and landlords all converging upon me claiming that I was a hoarder. All wishing to help relieve me from my copper. Well now I'm stuck in Michigan where I grew up and there are no surplus houses here and no way for me to rebuild my stock.
OMG! That was an easiest to understand explanation I ever heard! You should to be a teacher! Please, make something like "Tube Amps for dummies" course :)) THANK YOU SO MUCH!!!
i understand the safety and precaution emphasis but if you wire everything up cold, and then plug in. are you at risk? cause it's leaked onto the case?
Hello! Thanks for the very informative video, it's a very simple operation and yet I couldn't find a clear explaination until now. Unfortunately I don't have a variac, could I use multiple low voltage transformers (4.5/6/7/9/12v/24v) and then extrapolate?
Yes, the voltage/turns ratios are linear so you can use low voltages for the primaries and be safer. Even so, if you have a transformer with a ratio of, for example, 40:1 and you put 10 volts in the winding with the least amount of turns, you will still end up with 400 volts on the secondary. the other way around you would get only 1/4 volt (250 mV) so one always has to be very careful.
Great tutorial. How do you determine the push/pull load on useful tubes where it isn’t noted in the manual? Bogen liked to use 6AV5 and Grommes used 6GT5 which were not specifically designed for audio but for TV horizontal deflect circuits.
My first guess with the tubes is there were probably lots of the TV horizontal output tubes available and inexpensive and they are pretty tough tubes. I think cost was very important back in the day. Most any tube can be used for audio since inter-electrode capacitance and inductance values will have little effect on audio frequencies. RF tubes are designed with these inter-electrode values minimized so in general, RF tubes can be used for audio but not the other way around - with exceptions of course depending on the frequency. I have seen 6550's used in RF amplifiers for 160 and 80 meters but above the 80 meter band (3.5 to 4 MHz) audio tubes are probably not going to do very well. I have been asked the question several times lately about determining plate load for SE and PP amplifiers. In general I look at it this way. Mostly, we run our output tubes in class-A. Some will argue AB1 or AB2, etc but in the larger scheme of things it is still predominantly class-A. This is looking at it from the 40 thousand foot level. It is kind of like saying how far is it to Europe? If you want to know exactly, to the mm how far it is to a specific coffee house in Paris that is a slightly different question and the answer becomes mostly academic. I hope this makes sense. Back to class-A load impedance... A class-A amplifier draws virtually the same amount of current all the time - whether or not it is in idle condition or driven to the max level of output. With this in mind, it helps keep things simple and basically, R=E/I. Check out the 6L6GC datasheet attached and see that the minimum current is 40 mA and the max current is 44 mA for a class-A1 SE amplifier. frank.pocnet.net/sheets/127/6/6L6GC.pdf See that 250 volts at 44 mA is 5681.82 ohms of load resistance. This is a 5K transformer. With this said, you might want to use anything between 3.6K and 8K. You probably get slightly different "sound" for the audiophile ear, from each impedance, and we can choose what we like best. As the tubes get smaller like the 6AQ5, the impedance values get higher (into the 8K or 10K range) because the voltage is usually around 250 but the current is much lower so the impedance goes up as noted above. Similarly, for the bigger tubes like the KT88, for the same voltage, the current rises so the impedance is lower (maybe around the 3.6K mark). These values have been figured out and put into practice for many decades so it is easiest to just look at good designs and use the values they use for output transformer impedance - or just use what you have. Lastly, the receiving class of tube output transformers only come in about 4 or 5 values ranging from the 3.6K mark to 10K so you just choose what you think is best as the values are set (if you were building a car, you would use the size tires that are already made and not try to design a tire of specific mm size unless you are a tire company) and only with a special transformer winding company will you be able to get specific impedance values for transformers. Hope this helps.
In the single ended (which is Class “”A” by definition) example the recommended load resistance in most tube manuals is 2 to 3 times the plate resistance. The higher the ratio the lower the distortion.
I would like to know more about input mic transformers since I'd like to build mc phono step ups. Where's a good source? I wish there were videos like this about them.
The plate to Plate impedance is going to be double the plate impedance of a single tube however. A push-pull Transformer with 8000 ohms plate to plate impedance is like two single ended Transformers with 4000 ohms Plate winding in series connected together.
@El Paso TubeAmps I have pair of Jamo MFB 100 Speakers, both amps working great, but one oft the toroidal transformers is broken, there is no data written on the transformer. I measure 2x23,4 Volt on the intact transformer, with an without load (low volume) Power consumption is (according to the back) 120Watts According to the data sheet it's Nominal power Woofer 44Watts, Mid,23 Watts, Tweeter11Watts ------ Music output Woofer110Watts, midrange 55Watts, Tweeter 40Watts. The toroidal Transformer weights 1150g, 9cm Diameter. Which transformer should i buy 20X20 Volts 22X22Volts and VA?
Hello sir I need some advice you see over the years my car experienced lot back charge problems I fixed that by using lot diodes on ich device and put on the field wire for my alternator an diode with Puch button to manuali engage it when I turn on engine first I did notice my cheap voltage regulator and ignition module who is an 4pin GM module do not have zener diodes. The problem is I need kinde of system that can out put 2 different paths of electricity.I work lot on engine modifications .So I did in the past try out using ceramic capacitors on my hei ignition coil who is an e core type every thing was fine and good engine starts faster it appears lights are brighter and engine operates nice on centrain fuel types now the down side my alternator cutt in current gets confused in the past it wuld not shut off the charge indicator light unless I rew more my engine so I requare more engine rpm to charge my baterry and make that bulb turn off. So I did eventuali trow all that crap away and put an 10amp diode and push button switch to manuali operate my alternator but still I ques because my voltage regulator on the alternator is lacking an resistor and capacitor like the US version Delco 12si alternator should have I'm confused now how to counter that anoying effect? It's just bunch high voltage ceramic capacitors soldered together 1 side goes to ignition + side the other via toggle switch to ground basicali.I hoppe my starter motor does not have any thing to do with that strange effects because it's an magnet type with s/R starter selenoid .So I hoppe for any advice how can that by solved or if there is any possibility to build an multi center tap transformer with an alternator with frequency stabiliser basicali I want to use charging system form my lead acid baterry and use the second path to charge capacitor banks or an baterry that can not explode because I want my chassis no not get effected by back charge and just make my ignition system more variabel you know just to start better in winter time and tune spark for variuse fuel types if necessary small corrections. Only problem I have so far I don't if those transformers need to by grounded should I make virtual ground with relay not to get shocked true the chassis? I am honestly feed up with my crappy Delco alternator that thing isn't variabel at all and components fail so hoppe you understand my problem and can give my some advice how it culd by possibly achieved multiple independent out puts from an alternator or how to convert that thing possibly.I wasn't Shure but perhaps an external driven alternator amp or voltage booster might work driven by an 2 stroker engine or perhaps AC motor set up .Ya know just some sort of improvised starting asistance in winter time. So I do hoppe my question is not over complicated .I also thought there might by possibility to replace those shity components from Delco alternators to some thing more heavy duty industry parts like bridge rectifiers or voltage regulators who are not sensitive to ground static. So hoppe for your opinion about this topic.
Got a question You say the push pull 6V6 output transformer is a single ended load but a push pull primary. What would the OT be like for a amp with just one 6V6 instead of two 6V6. Could you make that OT work with just one 6V6 if you left off the center tap wire? Would the impedance be 8100 at 4 ohms without the center tap on the primary if it was just one 6V6? Does the center tap on the primary always mean it is a push pull OT? Thanks
The impedance of 8K ohms is from one side of the primary to the other so it would be 8K if you used the transformer with just one 6V6 in a Single-Ended (SE) configuration. You could use the CT to one side for a 4K primary. The output would still be 4 ohms. It gets a bit more complicated in that the secondary load actually determines the primary load. For example, if the secondary (speaker) load was 8 ohms, the reflected primary impedance would be 16K ohms instead of 8K ohms. Fortunately, these impedance values can vary considerably and still working amazingly well. Another possible issue in using a PP transformer in a SE circuit is that in a PP circuit the average current flowing in the primary is zero. That is certainly one of the good things about PP operation. The fact that the current flowing in the primary is, on the average, zero, (it is flowing in one direction for one tube and then the opposite direction for the other tube in PP operation) this means that there is no magnetizing current flowing in the primary winding so the transformer core will not become saturated and have the inductance drop to virtually zero (drop from maybe 10 H to just a few mH if saturated). It takes amazingly little current to saturate the core of even a very large output transformer. An educated guess in a transformer this size, probably 20 mA might saturate the core of the transformer rendering it worthless. So, the way SE transformers differ from PP transformers is that the SE transformers have an intentional gap in the core structure which allows for more current to flow before the core saturates. This unfortunately, (there is a Yin and Yang to everything...) makes the inductance in the SE transformers much lower than the same size PP transformer and low inductance causes a problem with low frequency response. With all that said, there are transformers that are labeled to work (so called, universal transformers) in either PP or SE operation. Lastly, it the transformer has a CT I think it can safely be considered a PP transformer. If you very carefully measure the DC resistance from CT to each side of the transformer, you will notice the DC resistance is not exactly the same. This is because it is necessary to have the same number of turns on each side of the CT but the wire wound on the outside portion of the core has a larger (ever increasing) diameter to be wound around and will necessarily require more actual length of copper wire, thus making the outer winding a little higher in DC resistance. Hope I made sense and this helps.
@@ElPasoTubeAmps Thanks for the reply. Very cool. I just got confused when I heard you say single ended while you were talking about that push pull 6V6 output transformer since I thought single ended meant one tube. I think I misunderstood what you said.
How would you suggest I cover the transformer wires inside ( under the bell covers) after I changed the wires. The sticky shellac like paper was covering the wires which I had to remove to change the wires. I'm not sure what to do. Thanks
I had to do something similar with the HV transformer for my Collins 32S-1 power supply, and other transformers. I have successfully used two layers of shrink tubing to both insulate from HV and provide a little tougher layer so that it does not, over time, work thru the insulation/shrink tubing to the case. The paper that was typically used as the original covering you describe is called fish-paper www.ebay.com/itm/122685484714?hash=item1c909feeaa:g:9eMAAOSwPhdVQ9pB I have no idea how it got that name but you could consider getting some if you want to add that extra layer of voltage and physical insulation or maybe just use thin cardboard ?? There is all kinds of good insulating material on Ebay. Here is another mica insulation www.ebay.com/itm/124766763516?hash=item1d0cadb9fc:g:gJ0AAOSwq~xf5KvQ of course, the mica sheets might not bend and conform very well. For truly high voltage wiring off transformer leads, I have had to use meter lead wire also. Meter lead wire is supposed to be good to a few KV insulation. For really high voltage wiring in a cabinet I use copper core spark plug wire. www.ebay.com/itm/224285678435?hash=item343877db63:g:aDAAAOSw8-Rf3lJY:sc:ShippingMethodStandard!79903!US!-1 www.ebay.com/itm/164802252713?hash=item265efacfa9:g:nYsAAOSw2MdfAd9T These links are just for thoughts and you probably want to shop around for the best prices. I recently bought the USA made copper core spark plug wire in a 100 foot roll for about 40 cents per foot. Hope this helps.
Great video sir!Thank you very much! I have a question.My amp is 5watt champ with 4ohm secmndary. What happens when I connect 8ohm speaker to it.The primary is has to be 8kohm.So connecting the 8 ohm speaker I'm actualy rising the primary impedance witch shoud lower my output power?What more goes wrong?:)Does the 6v6 start working beyond his limiths? Thank you very much!
love watching your videos... question... Mcintosh MC75 uses 2 kt88, but they are able to make the Zout to 600 Ohms..how can i make the same dual kt88 to have 1500 ohm zout? pls help... thanx a million...
Thank you. The output transformer has to have a secondary winding equal to 1500 ohms to have that Z output impedance. 1500 ohms is not a common value and for testing, you could try the 600 ohm connection and it should work. You may not be able to get full power output but it should work reasonably well. Here is the schematic for the MC75 where you can see the 500/600 ohm output is located on the output octal socket and taken from the cathode winding. Generally 500 and 600 ohm outputs are interchangeable and may be stated either way as they are close enough to each other. www.thetubestore.com/lib/thetubestore/schematics/McIntosh/McIntosh-MC75-Service-Manual-with-Schematic.pdf
Hi you, cool channel! Let me first say that I know nothing about electricity or how to build an amp, in future I'll get some techman to recreate an old '66 Marshall JTM45/100 (like the ones used by Hendrix at Monterey or Angus Young in the High-Voltage AC/DC album where he used a 675 Volt Marshall with KT66) by using vintage Partridge transformers instead Drake's. I always seen those Partridges going matched with EL34s. But now I'm wondering if '70s Partridge transformers (those ones used in Hiwatt DR103 amps) could match four KT66 tubes and their high-voltage stuff. Thanks
Thank you for a great and simple video. Are those calculations for both triodes SE and pentodes SE? I find it hard to understand, for example if that load resistance in the tube data sheet would be the same as transformer primary impedance - it would be perfect match, right? But when you take 12AU7 as a power tube for 1W "Micro Champ" built - which has approx 7.7k load resistance, it needs 25k primary.. Why?
There’s a difference between “Plate Resistance “ and “Recommended Plate Load Resistance” in tube manuals. For single ended triode amps the typical load resistance is 2-3 times the plate resistance. There’s no equivalent “rule of thumb “ that I’m aware of for pentodes..
Great video! Thanks. I like using old military tubes but sometimes have difficulty finding to A impedance or A - A. Do you know of any books/info that would help with this? Thanks.
I found all the books difficult in my education in the 1960's. Once a fairly advanced understanding is achieved, it becomes much easier to see what the writer was trying to express. There is good stuff on the Internet but there is also a lot of error so be careful. Probably the best source would be Amateur Radio Handbooks from the 1960's and 1970 time frame for discussion of tube fundamentals.
Hey Dave, my 1st post with you. Like Uncle Doug, I think your sharing these videos with the public is great! I'm sure you will help a guy like me to build my own tube amp. Safety is always the #1 consideration when working around the high volts in a tube amp. I have a question; if using a pair of 6L6s in push pull, and using the data sheet for a 6L6 and finding that it needs 6600 ohms of impedance from the primary of an OPT, do you need an OPT with a primary impedance of 6600 across the primary or from center tap to either lead, and how come the OPTs that I've looked at for replacement for output stages that have 6L6s are 4000-4500 ohms of impedance? Is there calculation you need to come to the correct impedance match for the 6L6s and the primary of the OPT? I feel stupid because I can't understand this. Thanks
Hi Hubert - thank you for your kind words. First, the impedance is from plate to plate across the complete primary. Secondly, your question about how the pros using primary impedances well below the RCA tube manual has baffled all of for decades. For the small 6V6 or 6AQ5 level amps, the tube manual seems to hold true and I recommend it. If you read articles on McIntosh amps, you will see that the primary Z of their transformers are as low as 1000 ohms. But then they also have windings that the cathodes are connected to - very complicated. I have personally found that all the pro amp makers seem to cheat the tube manuals in using primary Z both lower and higher than recommended. If you ask this question to an academic, they will simply spout out to you what the books say in the form of a maximum power transfer theorem - and they will be wrong. I have personally found from building amplifiers that the primary Z lower than recommended usually provides improvement (higher power output and lower THD) over the tube manuals recommendations. So, I haven't been much help at all. Maybe you can get a copy of, "Audio Cyclopedia" by Howard M Tremaine. It is an interesting book to go to bed with.
One thing about output transformer is the impendence rating are usually determined buy testing them at a set frequency like 400 cps. The output transformer is also an inductor driving an inductor (the speaker voice coil) as the frequency changes you will find the impendence on the primary of the output transformer will also change. Amp companies try a number of different transformer and then go with the one that works best for their amp/speaker combination. Hopes this helps.
Hi, LordKelvin100 - I think you have some really interesting questions and I will do the best I can to give you the information that I have as I understand it. Obviously, I do not know everything about vacuum tubes but I am always willing to share what I do know. I believe the best answer I have to your first question is, tube designers, in the beginning, simply did the math and gave us the theoretical values for maximum transfer of power theorem. Here is one reference: en.wikipedia.org/wiki/Maximum_power_transfer_theorem However, quality improvements in fidelity made it necessary to deviate from this method so, in the design of modern low distortion amplifiers, efficiency was sacrificed for fidelity. As for Class A vacuum tube amplifiers, the stated parameters there are simply that plate current flow for the entire cycle and it can be single ended or push-pull. We also have to remember that in the design of vacuum tube amplifiers as seen from RCA tube manuals, efficiency, and to some extent, fidelity, was paramount and the creative process of “crunch”, and “over drive”, and the such that the musician requires in the creation of music was not part of the vacuum tube design formula. I only add this comment for those that are interested in “the sound” rather than the purely analytical design as these two philosophies don’t coexist. As for Class AB (AB1 and AB2), the tube manuals will tell you that Class AB1 says that we are willing to drive the grid of the tube right to the point of grid current but we won’t cross that line-in-the-sand. This will give us a little more power output and increase our efficiency and allow us to advertise our amp at a higher level of power. Class AB2 says we will cross that line-in-the-sand and draw a small amount of grid current on peaks so, once again, increase our power at a little bit more distortion. I believe in reality, we have crossed the line into sales philosophy. As for Class B amplifiers, these amplifiers are designed and biased and the proper tubes are used for this purpose such that only one tube conducts at a time. Examples of good Class B tubes are the 811A and 3-400Z triodes. This increases efficiency and notch distortion and is primarily used in amplitude modulated (AM) radio stations. The increase in distortion is acceptable and the increase in power output and efficiency is worth the increased level of distortion. We also have to remember that the Receiving Tube class of vacuum tubes that we usually deal with are not designed for Class B or Class C service. They are designed to operate in the Class A, AB1 and AB2 class. There are a few basic designs that come to mind in vacuum tube audio amplifiers. The Williamson, Mullard, Dyncao and McIntosh. Some of these differences are primarily paraphrase vs long-tail inverter design and pentode vs triode. The McIntosh design is the most interesting and has a plate load Z of 1K ohms and a cathode load Z of 1K ohms. A beautiful design but cannot be duplicated without the McIntosh output transformer. Best article I have ever seen on the McIntosh design is in, Audio Cyclopedia, by Howard Tremain. I think your comment on hollow state design by formula is exactly right and is what I have tried to express and have experienced. We don’t disregard these approaches but modifying them by empirical design is why we are where we are today in the reality of vacuum tube circuits.
Hi Dave, I have a question about 2 output transformers I have and if they will work in a single ended application. I took them off of a pair of 10" speakers out of a 1966 JVC radio, reel to reel tape, radio console. The unit said Stereo, each transformer on one side has a common, 4 ohm an 8 ohm lead. The primary side has 3 wires, it says 5K and the middle wire is a Center Tap. Could I use them in a single ended amp with a 6V6 or 6AQ5 if I didn't use the center tap? Or will it not work? Im not sure what the center tap is for. Thanks, Tom
+Bucyrus Erie12 The center tap is connected to the power supply. The other two wires that connect to your output tubes are likely blue and brown. You will get audio output if you use it with one tube but the power level will be low and the low frequency response will suffer the most. The sum current through a PP transformer is basically zero so there is no saturation of the core. In a SE amplifier, the tube is run class A so there is constant current through the OPT and it takes amazing little DC current to reduce the effective inductance of the OPT to just a few millihenries. I would use it as a PP amplifier OPT and it will perform properly.
I tested my 1959 gibsonette GA-9 O coil using a similar technique and arrived at 27.5:1 With the stock speaker at 3.5OHMS Z= 756.25 OHMS 27.5 ^ 2 so P = 2647OHMS Z * 3.5 I cant find within the data sheets how this single ended dual 6V6 class A should be. The closest I saw was a triode config at 1960 OHMS
I know what you mean. Often times these impedance's are not what tube manuals call for. Not sure if you have ever run across the Fender amp that has a 1 ohm load. I think it is the "tweed" version of yesteryear. I don't remember all these instruments perfectly some times but I do remember it has four, 4 ohm speakers parallel. It runs a pair of 6L6's and will indeed put 50 watts into a 1 ohm load (7 volts RMS across a 1 ohm load). I had more than one "double take" the first time I ran across that amp. Also, 1960 ohms and 2647 ohms are not That far apart... :-) and maybe they did it on purpose (mismatch) for the tone quality... Who knows??? I have made quite a few transformer Z measurements, both voltage ratio and direct impedance bridge measurements and while the voltage ratio and Z bridge will compare pretty close, they hardly ever are exactly what the transformer manufacturer says the transformer is. Mostly, I would say, that everything is within about 5% and within the world of transformers that is pretty close.
This is my foray into guitar AMP as opposed to HI-FI with tight tolerances to limit THD. I read further that a 6V6 at 320V on the plate has an expected THD of 12% @ 5.5W. Considering I dont allow my dynaco equipment to pass > 1% until 30K, I find it kinda laughable.
I understand the crazy THD figures the manuals give. I am sure that is with no NFB or any enhancements like ultra-linear and everything else. We know the tubes will do a lot better than that. I did not start into guitar amps until I retired in 2010 and all of my experience was with HiFi just like yours. Well, the guitar amp is a whole different world. A "music creation" amp with 0.1% THD will never be accepted by the musicians. The harmonic profile of guitar amps is horrible and THD at rated power is never less than 10%. These little SE guitar amps from the 1950's have a triangular harmonic profile and everybody wants one just like them. You can practically throw all your HiFi experience out the window when it comes to guitar amplifiers.
So i get it.... Acoustics have their own harmonic characteristics, based on design and the type of wood used, and electric guitars require amps to produce distinct harmonics based on circuitry. I just finished an ST70 that ive tested on the HP331A averagingway below 1%, were gonna print it down to the guitar shop and plug it into two speaker cabinets. I wont bridge an ST70 because the monoblock performance is quite bad.
I was wondering whether it wouldn't be safer to avoid the variac/6V TX altogether and use an oscillator like your SG502 or SG505 on 50/60Hz as the voltage source. Is there something against that that says it won't work or is a bad idea? You can get about 5V out of them. I did this once to figure out the secondary phasing on a PTX and it seemed to work OK.
QuadMaestro I agree with you, it would be safer and pretty much any audio oscillator should work. The Z of the oscillator is high so the amount of current would be limited to very small amounts. I was a little reluctant to make this video as connecting the source voltage to the low voltage winding could easily produce HV on the secondary side. Thanks for your suggestion
Question: If you apply voltage to the primary side via the 6V transformer/Variac, why not to put 4 or 8 ohm load in the secondary side and then take the volt reading thru that load?
+Ramon Medina You could do that but it wouldn't change your reading. Putting a 4 or 8 ohm resistor in series with the secondary and then your meter across the resistor-secondary series circuit would only add the 4 or 8 ohms to the internal impedance of the meter which is probably 10 megohms or higher. Hope this makes sense. You would end up with the same reading even if the resistor were several thousand ohms.
How do you determine impedance ratios of small signal mic input or mixer output transformers? I’ve done it for unknown outputs that are used in tube guitar amps. Same way?
It would be done the same way but care should be taken when measuring these small transformers. Many have a rating of zero DC current thru their windings as there are thousands of turns of very tiny wire and I am sure could be permanently damaged by applying more than a mA (or less), of current thru the windings. I don't know this for a fact but I would suspect even a vintage VOM could saturate the cores of these transformers. Modern day digital meters are high Z and the voltage output to measure things like resistance is much smaller than the older ones that used dry cell batteries for the ohm meters and was a simple meter, resistor and battery circuit. With this said, I have been unable to measure some very sensitive (i.e., 20 uA) meter movement resistance values with high-end digital volt meters as their "computer" seems to "hunt" for some level of current that they can not obtain and end up giving false readings. Transformers around 100 years ago were a passive way of raising voltage as long as the load impedance was very high, well into the megohms. Manual labor and material was surely cheaper than vacuum tubes and the components used to build active amplifier stages back then. I would start by putting a very small AC voltage (100 mV?) in series with a 1 megohm resistor into the windings of one of these vintage microphone transformers to make sure current is very limited. You may have to tinker with that value of resistor somewhat and use your most sensitive and high Z volt meter to measure the input and (unloaded) output voltages of the transformer under test. If you can safely and accurately get that voltage ratio, then you square it and get the impedance ratio. Hope this helps and works for you. Just my thoughts on an approach at the moment.
hi i've being looking on the net about how to choose the right PT for instance like with caps to use for the power section and soforth any help would be much appreciated
It is just an extra step is safety so no matter how high one might accidently set the Variac, the voltage will be low and safe everywhere on both sides of the transformers. An example is measuring a voltage step-up of 0.1 VAC to 10 VAC is a (turns and voltage) ratio of 1:100 step-up which is the same as a 10 VAC to 1000 VAC ratio. My philosophy is, first thing is to stay alive and the second is not burn up the tubes... 🙂
It is usually a different color from the two "outside" wires of the HV secondary. Often times the HV wires are red and the center tap is red-yellow. Also, the DC resistance as read with a normal ohm meter will be approx 1/2 the value across the whole secondary and will be the same from the CT to each side of the secondary
That is an old Southern saying I probably heard from my grandmother. She was born in 1896 and my grandfather in 1892. That is where many of my root philosophies come from as they were the ones that raised me. I got plenty more sayins' like that.
I NEED YOUR ADVICE, I just bought a brand new BUGERA V22 HD amp. The guitar I used is an EPIPHONE LP "56 ReIssue with P-90 pickups. As I move around the room there is a HUMMM that goes from non-existent to very loud. Then I recently read an article about UNSHEILDED PICKUPS and how they can cause havoc on tone and signal interference. The finish and materials used on the body of this CHINA MADE LP guitar is really nice BUT we all know that Epiphone electronics is the worst. QUESTIONS - 1) Is it the guitar causing the different humms as I walk around the amp? 2) IF I wanted to change the PUPS would Mini Humbuckers FIT where the P-90's are so I would Not have to resize the PUP cavity? Thanks In Advance, Ade
that's 60 cycle hum that you're getting. its very normal. but can be intensified by a lot of different things. some things to check to try to reduce it are, is your amp plugged directly into a grounded socket in the wall? don't plug your amp into a surge bar or anything like that, it can/will make interference noise worse. are your pickup/control cavities shielded? if not, it wouldn't be a bad idea to shield them. if your pickups aren't "microphonic" then theres not really much that can be done about them as far as 60 cycle hum is concerned aside from grounding/shielding them better. is your cable a shielded cable or not? are you near electronics where you're playing (Tv's, stereos, anything with a transformer, and fluorescent lights can be the worst)? essentially, p90s are large single coil pickups, and single coils have a lot more hum by nature than humbuckers, humbuckers are called that because that's exactly what they do, they're 2 single coils wired opposite to cancle/reduce hum. I wouldn't damn the pickups per se, if they sound good to you and do what they're supposed to, theres no reason to ditch them. general the hum you're describing is from outside sources or improper grounding/shielding.
+a. webb - P-90s are single coil pickups so they will pickup and reproduce hum created by various fixtures but commonly the most powerful and close at hand is your power transformer in your amp. Shielding can reduce it some but because of oscillating magnetic fields of such power some hum will get reproduced by a single coil pickup. This is exactly why Seth Lover invented Humbucking-TM pickups which are dual coil where magnetically one coil is out of phase by 180 degrees so the hum in one coil will subtract from the hum in the other. If they are well matched the hum will be close to zero, but you also lose some of the brightness in the response to your guitar' strings. This is why a stock Telecaster or Stratocaster sounds brighter than say a Les Paul with Humbuckers. It is a tradeoff and only you can decide if the greater brightness is worth either the hum or the complexity of paying attention to where you stand or applying devices like compressors or noise gates.
Look at it this way - suppose you have a 200 VCT secondary and a 6 volt filament winding. That gives you a turns (or voltage) ratio of 200/6 = 33.33. Now square 33.33 and get an impedance ratio of 1111.11. Now if you put an 8 ohm load on the six volt winding you will get a reflected impedance back to the 200 VCT winding of 1111.11 x 8 = 8888.89 ohms or about 9000 ohms. if there are other windings on the transformer like a 120 volt winding and a 5 volt winding, just tape them off and ignore them - do not short them together... With this procedure in mind you will have to do some experimenting. This 60 Hz power transformer is not going to be a high-end HiFii transformer but it will produce audio. Hope this helps.
thanks a lot for this information. :) Anyway I have another doubts about these Transformers and I would like to know If you could help me via PM Thanks
i have a 213 magnatone out put sound almost 0 and i see light in all the tubes i think the output tubes look dimmer than the rest could you point me in what direction i should go to repair this.
Hi EIPaso TubesAmps I have a question that may sound silly. What is the difference between HiFi power transformers and Guitar tube amp PTF. While on that is there a difference between solid state PTF's and tube PTF? Thanks love to hear the answer :)
For vacuum tube power transformers, there would be no significant difference between HiFi power transformers and guitar amp power transformers. They both supply in the neighborhood of 450 volts DC to the plate of the tube and often times they have a separate winding or a tap on the HV secondary to derive a negative bias voltage for the grids of the output tubes. HiFi transformers may be potted for a nicer appearance but what is inside is the same in both cases. As for output transformers there is considerable difference as the HiFi output transformer should have a much wider frequency response than the guitar amp output transformer. I assume PTF is power transformer... if so, the difference will be voltage level. A typical 50 watt tube amp transformer might be 800 VCT at 200 mA whereas a solid state power transformer might be 80 volts at 2 amps. In each of these cases, that would be 160 volt-amps or approximately 160 watts. Hope this helps.
ElPaso TubeAmps frequency response that a amplifier plays has not a thing to do with what transformer you use. If you have a amp that both use the same tubes or transistors but one is a sub amp for low frequency say 40-80 HZ and the other covers 20-20,000hz the same transformer will run both amps.
Hi and thanks for the vid!My problem: can I replace the 2 output transformers of my integrated amp Bell 2420 in order to upgrade the sound?...Marked on them : impedance Pri :9500ohms CT, Sec: 16 ohms Tap ,8 ohms ,4 ohms.Many thanks
That is a tough question - the answer could be, "yes" if and only if, you could find an output transformer with better specs than the one in it now. The problem is, you probably cannot. The ultimate output transformers for PP 6L6's and the such are still made by McIntosh with their unique and patented design. I think the sane thing to do is experiment with different tubes. Changing the output transformer is like changing the compression ratio and cam timing on a car engine (and having the machine shop to fabricate these items...) It is just pretty much beyond all of us at the OPT level - nothing more than a random blind swapping with no repeatable way to confirm performance - I don't mean to be discouraging but many things are just what-they-are and true fundamental changes are not possible for us experimenters - hope this helps.
It is actually fairly simple to get a good ball-park rating on a transformer but it is hard to put into just a few words. Transformers are rated in volt-amps (VA) which is AC volts multiplied by AC amps (RMS values of both) this gives what is called "apparent power" but for all practical purposes for the small transformers that we use, the VA rating the power rating (in watts) is the same. Try to keep things simple. As mentioned in this video, first look carefully at all the data written on the transformer. It it does not have specific ratings on it, maybe an Internet search on a manufacturer and part number will give you some good information. If you know the equipment it came out of, you may be able to determine something about the transformer from that data. I want to be careful not to mislead you and give you information that is not reliable but here is some data to think about. I am considering a UTC CG-301 transformer. It weighs 15.5 pounds and is rated at 200 watts. See the attached UTC transformer catalog, page 47. You could, for ball park values, use this as a model. In other words a transformer weighing half that weight (about 7.5 pounds) would be good for about 100 watts and so on. It is a place to start. After this information, you will have to do Ohm's law equations using voltage and current and power to determine the unknown value you need. Also, be very careful with transformers. They are no more dangerous than a rock when unplugged but when plugged in, HV from transformers can be death-on-contact. For a practical example, lets assume a transformer of about 7 pounds (100 watts) which has a 6.3 volt 3 amp, a 5 volt 3A, and a 600 volt HV secondary that you do not know the current of. The 6.3 volts at 3 amps is 19 watts, the 5 volt 3 amp is 15 watts so you have about 65 watts left for your HV winding. I = W/E so this gives I = 65/600 = 0.110 or about 110 mA. This should be a pretty conservative rating. Hope this helps. UTC catalog vk1nam.wordpress.com/yaesu-ft-857d-menu-settings/
i have a question based on your comment of more amps than the law allows and that is could you tell me what the wires are on a K70749 power transformer that came out of a conn minuet 541 organ? i figure the 2 black are primary, and i also figure the green wires are 6.3v and the green/yellow stripe wire is the ct for the 6.3v. the wires i dont have a clue of and need help id with are the following: 2 ) wires are either orange or brown cant really tell but they are twisted together, next are a red and red/green striped ( also twisted together), a yellow and yellow red stripe ( which are twisted together) and lastly is a blue wire. i have been looking all over the net and i have not been able to find anything.
+lordraptor11 I don't think you are likely to find that exact transformer anywhere on the Internet but you are better than half way there already. I, too, would bet the black wires are the primary so I would (carefully, maybe with a 100 watt light bulb in series with the winding if you don't have a Variac) connect it to an AC power cord and with a voltmeter capable of measuring 2000 volts or more, probably not a modern day digital meter, start measuring the red, yellow/red stripe, etc wires and drawing out the schematic. It's not that hard and I suspect between the red/red you will get 800 to 1000 volts or more with the red/yellow the CT, etc. I have no idea what the blue wire would be but you will find out with careful measurement - possibly a 120 volt, or so, tap for a bias supply (?) Be careful, 1000 volts can be very nasty and even deadly.
Hi Dave, As usual, I always enjoy your videos..I agree with you 100% about over emphasizing safety while working transformers. Just because the transformer is sitting on the bench and outside of an amp, makes it no less dangerous. Even those who have been in the biz for decades need to always be mindful that one stupid mistake could be your last.. I don't want my epitaph to read,' Here lies a guy who was so stupid that he electrocuted himself even when he knew better...LOL. Better to read, " Here lies a guy who died of a heart attack AFTER making love to his wife on his 104th birthday. If only he had stopped after the 5th time that morning....LOL Well, if you are going to dream, lets do it RIGHT!!!!!!
Glenn - you sure got it right... my motto is, “Live like a rock star and die quickly” (but not with HV,,,) As much of a pain as I can be to the family, I don't want them to find me next morning still sizzling on 3 KV which, if they touch me, they just might be meeting me Upstairs. I really have a lot of fun with YT and have met a great bunch of guys. Always enjoy hearing from you. Ohh... and just in case if we don’t die after five times with our wives then maybe just four times in a menage a trois with ladies half our age and preferably a heart attack and not shot by jealous boyfriends :-))
so if i am winding a transformer and i want say 6000 ohm primary to 6 ohm speaker how do i know the minimum turns on secondary. i understand the ratio and impediance but you never see a one turn winding, its always multiples
Do you troubleshoot small 50 watt amps Ive got a pair which are identical builds but do not pass sound I think its jumper related or something's fried the OT on both but I dont think thats it I think im missing jumpers. I get voltages and close readings but no sound. Near Dsllas area... thanks.
I don't take in equipment anymore. Just too much to receive and reship and I have become unreliable. I would like to help you but it is difficult to do over text even though, as you say, it may just be a jumper problem. Can you "Google" the manual for the amplifiers?
Do you repair transforms? I have a large power transformer that feed large 1000watt power amp and pre amp on jukebox unfortunately evertime I connect power supply to it it kicks breaker on power supply. The transformer doesn't smell burnt and sure looks fine. This transformer has many wires and hard to find another is it possible to rebuild or should I just use three separate tranformer instead of one large. Thanks
I do not repair transformers. However, let me tell you a quick story. I have a Collins power supply for the S-Line equipment that is about 2000 volts CT and feeds a 5R4 rectifier. This power supply has given me trouble two times ( I have made two videos of it) and each time the transformer appeared shorted but as with yours, never smelled bad. The problem was, the thin insulation on the 2000 volt secondary winding was arcing between the wires (not go ground). Do a very close visual inspection of your problem and you may find a similar problem. To finally solve my problem, I cut the secondary wires off as far down into the transformer as I could safely and still have room for connection and then extended these wires with high voltage meter lead wire and extra shrink tubing insulation at the connections. It worked. Also, you may simply have an external short that you have not noticed yet. You may have to disconnect all of the secondary wires from the transformer to determine if it is indeed a bad transformer or an external short on one or more of the secondaries. Hope this helps..
Can i ask you something? First of all thanks for video. I have 6 output transformers that was in televisions with pcl86 tubes. I wish to biuld amplifier but all schematics i find use 5k primary. When i check mine its 350-450 ohms primary but i remove thdm from working televisions. Can i use 350 ohms primary and be safe?? I mean its supose be 5k or its normal to be 350 ohms? I dont believe 6 are bad because i remove them working. Thanks
You are measuring DC resistance instead of AC impedance. The first thing to know is are your transformers made for a single output tube or two tubes in push-pull. A very common value is 5K impedance from one plate lead to the other plate lead for two tubes in push pull. Transformers made for one output tube, like a 6AQ5, 6BQ5/EL84, 6V6 or 6L6 are pretty high impedance like 8K or 10K but push-pull transformers are more in the 5K to 8K range. Absolute optimum impedance is nice but often times not realised with what we may find in old equipment but even if the impedance is off somewhat, it will still work OK. Old output transformers if they are push pull (made for two output tubes) often time have a blue wire for one tube, a brown wire for the other tube and a red wire for the center tap (CT) that goes to the power supply high voltage, on one side of the transformer and maybe a black and green wire on the other side of the transformer for the speaker connection. Single ended transformers (made for only one output tube) will likely have two wires on one side for the tube (the 350 ohm winding as you found) and the other side will likely measure almost like a short circuit as it is made for 4 ohms impedance (not to be measured with an ohm meter). My guess is your transformers are for one tube and should work with any of the smaller tubes like the PCL86 tube. Once you figure out if your transformers are single-ended or push-pull I may be able to help you further. Hope this helps.
@@jonathangauci2182 Here is one of my videos that may drive you crazy or you may like it - th-cam.com/video/CJ__UfPMG2Q/w-d-xo.html On the other hand, you can buy an impedance meter like the MS5308 LCR tester as I show in this video which makes it much simpler. th-cam.com/video/HV_6gmaZDF8/w-d-xo.html
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If this guy doesn't teach electronics, he should. I am a retired Electrical Eng., and this was the most basic (yet informative) explanation I've ever heard. Anyone watching it, and then not having a good understanding of " Turns Ratio ", was either not paying attention, or needs to find another hobby.... Jim
A mysterious topic explained so lucidly for a layman. Thank you very much for sharing.
So that green/white wire hanging under my transformer is a center tap! I never found a schematic for this amp (1956 Ampeg GuitarAmp , according to the serial number). The wire was coiled in a corner unconnected to anything. I connect that to GND thinking it might be a transformer case ground and the amp lost a good amount of its background hum. The rest of the hum disappeared when I ran two 100 ohm resistors from the 6vac filament lines to ground. What a difference! It is a pleasure to play on this amp....so quiet. Thank you for all the great practical information.
This is just what i needed to brush up on my old electronics knowledge so i can finally build a little SE el84 amp. Thanks so much.
Most my clients are mystified by transformers. I think you covered the subject pretty well and kept it simple in layman terms. Good job.
Dose in push pull 8k push pull turn ratio for 4 ohms it's 45:1 weather in single ended 8k will be 45:1 or half of that for 8 ohms
I actually did this on a Milbert car tube amp to verify the output transformers are the same as the old Berning EA-230 schematic (6.5K). I read the info online but your video was more "real" and very helpful. Thanks!
Thank you very much for posting this. Us younger guys feeling our way through the dark with this appreciate all you more experienced guys, your knowledge, and your sharing this with us!
This is a great way to both to check a transformer for ratings AND to check if the transformer is blown. Thank you for sharing your knowledge and experience. This was extremely helpful!! Gratitude.
Nice & simple video that really teachs something practical to the tube and transformer user's community. Congratualtions !!
I just wanted to thank you for taking the time to make this video. It's very informative and useful.
Thanks David. I'm looking at some of your older videos. Good stuff here. 1) I like the fact you twist your wires. I do this with all my wiring except the blue and brown wires on OTs typically used for plate connections on tubes. I think these two should be separated. 2) it's the same safety consideration with soldering. I have burned myself too many times to count. It was usually when I was distracted and not paying strict attention. I had to educate my other half to not disturb me when soldering :-) Also, if your soldering iron slips out of your hand for any reason and lands on a component, that component may be destroyed. I know from experience. Easy to understand explanations in this video. Good job.
No truer words when working on HV. I was bit by an operating microwave transformer, 2,400V 1000 watts when my shop assistant was yapping in my ear rather than doing his own work. The only reason I am alive is because I followed rule #1, keep 1 hand in your pocket, and wear insulated shoes. It hurt like a son of a bitc- and threw me about 6 feet.
The second time I was walloped by the 2nd anode of an operating picture tube because the same assistant didn't clean off the glass, and 2nd anode cup before attaching it. Debris on the glass set up the perfect storm for a bolt of lightning to do a number on my hand, and split my thumb nail in 2. That one felt like hitting my thumb with a hammer.
Needless to say my shop assistant was flipping burgers after that. I actually enjoyed firing his ass.
12voltvids thank your lucky stars you were alive to fire him,lol
Glad you're still with us to tell us about it - and produce a great video series too.
OUCH!
@@radiojet1429
You know when a soldier says he re-lives battles, and firefighters say they re-live fires or bad accident scenes, and police officers re-live horrible crime scenes. PTSD is real. For years I would have vivid dreams of grabbing a live wire and not being able to let go. One time I threw my arm out trying to break the current and hit the wife who was sound asleep. She wasn't happy.
@@12voltvids I believe I am subscribed to you. I send you vibes of comfort and joy.
Some people think they know ...........YOU SIR are well......... unreal........I truly love your videos and before you I did not think I would ever grasp all this craziness.... I am starting too and I sure appreciate it.
If you ever build another kilowatt or whatever huge amp, love too document what it sounds like with a guitar through it. I have guitars and will travel. I love ya brother. I would love too be the first man too play guitar through one of those crazy amps.......I think it would make a lot of noise in the guitar world...get it........Thanks so much.......
One of the challenges of building efficient class B audio vacuum tube amplifiers is the fact that the output impedance of the tubes varies with conductance, which varies with screen grid voltage and control grid voltage. It's one of the things that creates nonlinearity in tube amplifiers. Making matters more challenging, imagine you're using MOSFETs to control screen voltage dynamically to respond to program peaks while keeping screen voltage low at idle, so the idle power is low. In reality, high fidelity and efficiency lie on opposite ends of the spectrum. It takes clever engineering to cancel out many of these distortion inducing technologies to make an amplifier that is both efficient and high fidelity.
Great video. I just did this on a used transformer I recently picked up to test. I don't have a variac, so I put a light bulb socket in series with the power transformer and ran the output off the 6.3 filament taps. Worked perfectly.
I think it is worthy of mention that because Impedance is the term used for alternating current as opposed to Resistance for Direct Current and both exist on the primary o an Output Transformer and because the impedance of speakers is dynamic - varies with frequency - the actual dynamic impedance of the load on the Primary and therefore on the Plates, varies as well. Also if you notice that the "required" P to P load impedance of a given tube changes with both DC voltage and Class of Operation (Class A needs a higher load Impedance than Class AB or Class B) and what this translates to is the linearity of frequency response under those dynamic conditions, it can be seen that it is safe to use a higher impedance speaker than was originally designed for, especially if you wish to increase supply voltage different than the example in the book or if you'd like to try a different Class of Operation.
For example it has long been noted than guitar amplifiers in which some kinds of distortion (non-linear response) are desirable can often benefit by plugging for example an 8 Ohm speaker into the 4 Ohm Jack/Secondary winding. It will likely be necessary to adjust the bias voltage to get the best sound or to get to Class A responsiveness but if you don't go overboard and/or monitor current conditions while playing, you can discover new tonality and distortion characteristics in your amp. YMMV but this is one advantage of Vacuum Tube amps which require Output Transformers as opposed to Solid State most designs of which eliminate the Output Transformer. Output Transformers are one reason Tube amps sound different from Solid State amps... not the main reason, but one reason.
The impedance changes with the frequency. I own a digital diplay LCR bridge and a variable AC power supply. The power supply reflects a load from 1 Ohms to 1000 Ohms, @ 1-1000Hz. The bridge will send AC signals from 1Hz up to 100KHz. Some of the audio transformers are impedance rated for ____ Ohms at 100 Hz, 400 Hz, 600Hz (600Hz is the old telephone company standard) or 1000 Hz. A non-inductive DC resistance load is not at all the same as a reactive inductive/capacitive speaker load. That load changes with the frequency. An 8 Ohm speaker can swing from 3 or 4 Ohms up to 13 or 14 Ohms IMPEDANCE.
Ty, really appreciate your advice - Thank You.
The short of it is 1) 30% of my house electrical system has not been updated, and 2) to save on the electrical bill we have all curly Q florescent light bulbs which REALLY DOES save us considerable money. I know both those situations cause havoc on guitars and amps. STORY HAS A NICE ENDING THOUGH - My friend loved the guitar and asked me to sell it to him. I told him to check it out at his house on his amp first to make sure everything was OK, and it was...
those lights are terrible for your eyes...all 'blue spectrum' no reds or orange....they also disrupt your circadian rhythm., making you not sleep....
i loved them at first....they are cheap and REALLY bright....but then i started having problems, detached retinas, stuff like that.....the old incandescent bulbs are SO much better for you.
Very informative video! Thanks a lot! It seems I'm not the only one who see similar interesting stuff here and at Uncle Doug's. I'm glad I found both of you! :)
Yes Uncle Doug is great. Check out D-Labs - his audio construction videos are worth watching.
@@radiojet1429 Yep, I watch him too! And many others :D
@@nusior Cool, my fiend - thanks!
Thanks for the advice on safety when working with high voltage. Same rules apply when doing anything critical/dangerous, I would add.
I have three of these beauties now. One measures up to 6KV and the other 5 KV. I "smoked" one not too long ago by measuring an audio voltage out of a modulation transformer that was a bit over 2000 volts AC but it was at 1 KHz. That was a bad idea. It arced the switch and I was finally able to find it and scratch the carbon of with dental tools. I kept a paper schematic inside the meter and it almost caught it on fire. It works proper again now but I don't use it any longer for HV measurements. High voltage at virtually any audio frequency will arc much further than 60 Hz and I knew that but thought it wouldn't happen.
Awesome video and great explanations on how to measure unknown transformers. And for sure you never can warn people enough about the dangers of high voltage! But there was a little mistake with looking up the numbers on the single ended one.
You were looking up plate resistance in the book which is not the right value. It must be load resistance. And you were looking up the 6AQ5 in triode connection which needs a different value as well. Plate resistance for the 6AQ5 at 250V Class A is appr. 52kOhms while load resistance is about 5kOhms. For a 6BQ5 or EL84 load resistance is typically 5,2kOhms while with different Bias settings you can also use 4.5kOhms or 7kOhms. So in the end it will fit for both tubes at 8 Ohms secondary.
+Pentode3000 I have to agree with you. Looking in the tube manual again, I see I looked at the plate resistance instead of the load resistance. I do appreciate you pointing it out and I hope others see this correction. If I can figure out how to insert an information bubble in the video I will make this correction.
Thanks so much for this information on Transformers I think this will really help me in that I consider myself to still be a novice at building repairing and troubleshooting tube amps but I really love this hobby I love music and I think this is truly going to help me. Right now I am working on a silvertone tube amp that came out of an organ from probably the mid to early 60s, I have two of these amplifiers that are identical and they use 6 B Q V output tubes two of them in the output but all the connections are made on the side of the amplifier through a plastic block that couples with another one and of course I don't have a schematic for this amplifier and I'm trying to locate one now but I'm also trying to figure out where the speaker leads would connect and also the volume and tone connections as well. I think this will give me a good idea of what is what and I'm going to try to sort it out from there, thanks so much for the video, great job.
For 08:48, this is a beauty! It is for driving transmitting tubes with grid current:) :)
The easiest way to get some serious power out of them is use AB2 with grid current is an interstage transformer....With the grid center tap goes to the bias voltage, or may be ground if you going to power up some 1k or more plate dissipation tube-beasts;)
At around 1:15, you described the configuration with a cap to ground on either side of the choke as a choke input filter. I know you know the difference and that it was a slip, but for those that don’t, it is a capacitor input Pi filter.
Thank you... this is important as mistakes can confuse a new-comer. TH-cam took away the ability to add speech-bubbles a few years back as they do not show up on remove viewing devices like iPhones/smartphones, etc (only computers) and apparently that is what most videos are watched on, so now when we make an error in our posting, we can't add that speech-bubble and correct it.
I used your formula again today on an audio transformer. Thanks again!!!!!!!!!!!!!!!!!
I built a project ecc83 and 2 el84 amp from an old philips mains transformer the design came from online very low component count but i was too poor to buy output transformers i had 2 matching 230v mains transformers laying around Big ones and worked out if i could use them size of them was overkill for 2x5 watts but the secondary windings worked out perfect for 8 ohms or 4 ohms as it had a centre tap on the secondary I fired it up and it sounded great powerful too considering i used my TDL rtl3 speakers that are no so efficient But then i read that good se transformers have air gaps something to do with the magnetic flux in the core of the transformer. so i looked up how to do that.its air gaps between the E and I metal plates.So i took all the Es and Is out and stuck thin strong sort of stiff cardboard on all and then packed them all back in.And the result was mind blowing.since then 20 years ago i have owned a lot of high end equipment.I love class a so expensive equipment. But i have never heard since the quality of the little amp i made myself.playing a beatles CD you can always hear the difference between john and paul .but with my home made amp the difference was much more like they were singing right in front of you.
I understand what you mean. Some of the amplifiers I have built that I like the most usually do not test out to be perfect on the bench. A perfect example of that is a SET amplifier. THD is always higher than any decent push-pull amplifier but the SET may have a "magical" sound to it the PP amplifier does not have. I have plenty of high-end equipment but I listen to my homebrew 7591 stereo amplifier using the UTC output transformers. For reasons I can not exactly explain, I prefer it over my McIntosh tube amps. Thanks for your thoughts and comments.
Thanks for a great video. I have just started working on Hi-Fi tube gear, and this really helped me a lot [beer-clink]
In every video u explain thing so brief it's so generic thing appreciate your knowledge and experience
I really appreciate this kind of video... dum dums like me can understand. a lot of videos on youtube that guy is just talking over everybody else's head. but this.. this is my pace.
Thanks for posting this. Very helpful. And I think it's great that you reiterate the safety points. Be well.
That’s exactly what we wanted to know!
WHAT IS IT AND WHAT CAN WE DO WITH IT!
Thank you.
I just spent a couple hours looking this up. Reading everything you explained here. I did all the math per what I read and wasn't sure if I did it right....Then I find this video and confirmed it. I have a few more OT's I can go figure out now.
Thanks again.
Thank you for producing this practical tutorial
Nice video! I like the US style of transformers, since here in germany usually transformers have soldersupports points instead of outcommin´ wires.
very good and informative explanation here ,so good I had to subscribe to your channel ,im a 1st timer but it def wont be the last time ,thanks for your great teaching knowledge
uncle doug is a great teacher as well ,between the 2 of you im learning alot ,I have had electrical therory being a commercial electrician ,and your right you dont want any distractions when working with high voltage can def relate to that ,i have installed breakers in 480 volt panels before that couldnt be turned off and you dont want anything or anyone around you
May 2nd, exactly on my birthday, nice...
You can use Power Transformer as an output transformer as long a you do not overdrive the magnetic field. I used center tapped (good to have 230V AC mains, i can use 120V two winding or centertapped transfomers) or two times winded Mains transformers a lot to test some pushpull amplifiers without the need of an expensive OPT in the first place;) But this is for experienced "tubetinkers" only;)
Did any of this come out of Friendship-7? I did not belive about putting my hand in pocket until one day I put both hands on my amp...Keep up the Lessons. Thanks so much...
you're explaining right at my speed 👍
also that was pretty cool how you did that one hand braid on that secondary at 16:20
I had a nice collection of transformers out in California. I had a reasonably good job and a house too.
Then the economy turned just enough that I wasn't able to sustain my house. Then I found myself living in an equipment yard in a box truck battling all manner of thieves, tweakers, recyclers and landlords all converging upon me claiming that I was a hoarder. All wishing to help relieve me from my copper.
Well now I'm stuck in Michigan where I grew up and there are no surplus houses here and no way for me to rebuild my stock.
OMG! That was an easiest to understand explanation I ever heard! You should to be a teacher! Please, make something like "Tube Amps for dummies" course :)) THANK YOU SO MUCH!!!
THANK YOU SO MUCH! Extremely helpful ! Great Video
Non-electronic question here... very nice video quality, what's the camera?
Thank you - I use a Leica V-Lux 3. Certainly not a German made Leica M or S series but for the money, I really like it.
i understand the safety and precaution emphasis but if you wire everything up cold, and then plug in. are you at risk? cause it's leaked onto the case?
Learned more about death, ahmm. I mean power trans vs output trans vs choke than any video on TH-cam. Only 6mins in
Hello! Thanks for the very informative video, it's a very simple operation and yet I couldn't find a clear explaination until now. Unfortunately I don't have a variac, could I use multiple low voltage transformers (4.5/6/7/9/12v/24v) and then extrapolate?
Yes, the voltage/turns ratios are linear so you can use low voltages for the primaries and be safer. Even so, if you have a transformer with a ratio of, for example, 40:1 and you put 10 volts in the winding with the least amount of turns, you will still end up with 400 volts on the secondary. the other way around you would get only 1/4 volt (250 mV) so one always has to be very careful.
Great tutorial. How do you determine the push/pull load on useful tubes where it isn’t noted in the manual? Bogen liked to use 6AV5 and Grommes used 6GT5 which were not specifically designed for audio but for TV horizontal deflect circuits.
My first guess with the tubes is there were probably lots of the TV horizontal output tubes available and inexpensive and they are pretty tough tubes. I think cost was very important back in the day. Most any tube can be used for audio since inter-electrode capacitance and inductance values will have little effect on audio frequencies. RF tubes are designed with these inter-electrode values minimized so in general, RF tubes can be used for audio but not the other way around - with exceptions of course depending on the frequency. I have seen 6550's used in RF amplifiers for 160 and 80 meters but above the 80 meter band (3.5 to 4 MHz) audio tubes are probably not going to do very well.
I have been asked the question several times lately about determining plate load for SE and PP amplifiers. In general I look at it this way. Mostly, we run our output tubes in class-A. Some will argue AB1 or AB2, etc but in the larger scheme of things it is still predominantly class-A. This is looking at it from the 40 thousand foot level. It is kind of like saying how far is it to Europe? If you want to know exactly, to the mm how far it is to a specific coffee house in Paris that is a slightly different question and the answer becomes mostly academic. I hope this makes sense. Back to class-A load impedance... A class-A amplifier draws virtually the same amount of current all the time - whether or not it is in idle condition or driven to the max level of output. With this in mind, it helps keep things simple and basically, R=E/I. Check out the 6L6GC datasheet attached and see that the minimum current is 40 mA and the max current is 44 mA for a class-A1 SE amplifier. frank.pocnet.net/sheets/127/6/6L6GC.pdf
See that 250 volts at 44 mA is 5681.82 ohms of load resistance. This is a 5K transformer. With this said, you might want to use anything between 3.6K and 8K. You probably get slightly different "sound" for the audiophile ear, from each impedance, and we can choose what we like best.
As the tubes get smaller like the 6AQ5, the impedance values get higher (into the 8K or 10K range) because the voltage is usually around 250 but the current is much lower so the impedance goes up as noted above. Similarly, for the bigger tubes like the KT88, for the same voltage, the current rises so the impedance is lower (maybe around the 3.6K mark). These values have been figured out and put into practice for many decades so it is easiest to just look at good designs and use the values they use for output transformer impedance - or just use what you have. Lastly, the receiving class of tube output transformers only come in about 4 or 5 values ranging from the 3.6K mark to 10K so you just choose what you think is best as the values are set (if you were building a car, you would use the size tires that are already made and not try to design a tire of specific mm size unless you are a tire company) and only with a special transformer winding company will you be able to get specific impedance values for transformers. Hope this helps.
In the single ended (which is Class “”A” by definition) example the recommended load resistance in most tube manuals is 2 to 3 times the plate resistance. The higher the ratio the lower the distortion.
I would like to know more about input mic transformers since I'd like to build mc phono step ups. Where's a good source? I wish there were videos like this about them.
Easy to follow. Thanks!
The plate to Plate impedance is going to be double the plate impedance of a single tube however. A push-pull Transformer with 8000 ohms plate to plate impedance is like two single ended Transformers with 4000 ohms Plate winding in series connected together.
@El Paso TubeAmps I have pair of Jamo MFB 100 Speakers, both amps working great, but one oft the toroidal transformers is broken, there is no data written on the transformer. I measure 2x23,4 Volt on the intact transformer, with an without load (low volume) Power consumption is (according to the back) 120Watts
According to the data sheet it's Nominal power Woofer 44Watts, Mid,23 Watts, Tweeter11Watts ------ Music output Woofer110Watts, midrange 55Watts, Tweeter 40Watts. The toroidal Transformer weights 1150g, 9cm Diameter.
Which transformer should i buy 20X20 Volts 22X22Volts and VA?
Hello sir I need some advice you see over the years my car experienced lot back charge problems I fixed that by using lot diodes on ich device and put on the field wire for my alternator an diode with Puch button to manuali engage it when I turn on engine first I did notice my cheap voltage regulator and ignition module who is an 4pin GM module do not have zener diodes. The problem is I need kinde of system that can out put 2 different paths of electricity.I work lot on engine modifications .So I did in the past try out using ceramic capacitors on my hei ignition coil who is an e core type every thing was fine and good engine starts faster it appears lights are brighter and engine operates nice on centrain fuel types now the down side my alternator cutt in current gets confused in the past it wuld not shut off the charge indicator light unless I rew more my engine so I requare more engine rpm to charge my baterry and make that bulb turn off. So I did eventuali trow all that crap away and put an 10amp diode and push button switch to manuali operate my alternator but still I ques because my voltage regulator on the alternator is lacking an resistor and capacitor like the US version Delco 12si alternator should have I'm confused now how to counter that anoying effect? It's just bunch high voltage ceramic capacitors soldered together 1 side goes to ignition + side the other via toggle switch to ground basicali.I hoppe my starter motor does not have any thing to do with that strange effects because it's an magnet type with s/R starter selenoid .So I hoppe for any advice how can that by solved or if there is any possibility to build an multi center tap transformer with an alternator with frequency stabiliser basicali I want to use charging system form my lead acid baterry and use the second path to charge capacitor banks or an baterry that can not explode because I want my chassis no not get effected by back charge and just make my ignition system more variabel you know just to start better in winter time and tune spark for variuse fuel types if necessary small corrections. Only problem I have so far I don't if those transformers need to by grounded should I make virtual ground with relay not to get shocked true the chassis? I am honestly feed up with my crappy Delco alternator that thing isn't variabel at all and components fail so hoppe you understand my problem and can give my some advice how it culd by possibly achieved multiple independent out puts from an alternator or how to convert that thing possibly.I wasn't Shure but perhaps an external driven alternator amp or voltage booster might work driven by an 2 stroker engine or perhaps AC motor set up .Ya know just some sort of improvised starting asistance in winter time. So I do hoppe my question is not over complicated .I also thought there might by possibility to replace those shity components from Delco alternators to some thing more heavy duty industry parts like bridge rectifiers or voltage regulators who are not sensitive to ground static. So hoppe for your opinion about this topic.
Got a question You say the push pull 6V6 output transformer is a single ended load but a push pull primary. What would the OT be like for a amp with just one 6V6 instead of two 6V6. Could you make that OT work with just one 6V6 if you left off the center tap wire? Would the impedance be 8100 at 4 ohms without the center tap on the primary if it was just one 6V6? Does the center tap on the primary always mean it is a push pull OT? Thanks
The impedance of 8K ohms is from one side of the primary to the other so it would be 8K if you used the transformer with just one 6V6 in a Single-Ended (SE) configuration. You could use the CT to one side for a 4K primary. The output would still be 4 ohms. It gets a bit more complicated in that the secondary load actually determines the primary load. For example, if the secondary (speaker) load was 8 ohms, the reflected primary impedance would be 16K ohms instead of 8K ohms. Fortunately, these impedance values can vary considerably and still working amazingly well. Another possible issue in using a PP transformer in a SE circuit is that in a PP circuit the average current flowing in the primary is zero. That is certainly one of the good things about PP operation. The fact that the current flowing in the primary is, on the average, zero, (it is flowing in one direction for one tube and then the opposite direction for the other tube in PP operation) this means that there is no magnetizing current flowing in the primary winding so the transformer core will not become saturated and have the inductance drop to virtually zero (drop from maybe 10 H to just a few mH if saturated). It takes amazingly little current to saturate the core of even a very large output transformer. An educated guess in a transformer this size, probably 20 mA might saturate the core of the transformer rendering it worthless. So, the way SE transformers differ from PP transformers is that the SE transformers have an intentional gap in the core structure which allows for more current to flow before the core saturates. This unfortunately, (there is a Yin and Yang to everything...) makes the inductance in the SE transformers much lower than the same size PP transformer and low inductance causes a problem with low frequency response. With all that said, there are transformers that are labeled to work (so called, universal transformers) in either PP or SE operation. Lastly, it the transformer has a CT I think it can safely be considered a PP transformer. If you very carefully measure the DC resistance from CT to each side of the transformer, you will notice the DC resistance is not exactly the same. This is because it is necessary to have the same number of turns on each side of the CT but the wire wound on the outside portion of the core has a larger (ever increasing) diameter to be wound around and will necessarily require more actual length of copper wire, thus making the outer winding a little higher in DC resistance. Hope I made sense and this helps.
@@ElPasoTubeAmps Thanks for the reply. Very cool. I just got confused when I heard you say single ended while you were talking about that push pull 6V6 output transformer since I thought single ended meant one tube. I think I misunderstood what you said.
Those big gray transformers look big enough to power an SVT and a half!
Thanks for another link sir...i'm a biginer tube audio...thanks again
Superb tutorial,sound theory.
I have the same Triplett 630NA..my fave multimeter..
How would you suggest I cover the transformer wires inside ( under the bell covers) after I changed the wires. The sticky shellac like paper was covering the wires which I had to remove to change the wires. I'm not sure what to do.
Thanks
I had to do something similar with the HV transformer for my Collins 32S-1 power supply, and other transformers. I have successfully used two layers of shrink tubing to both insulate from HV and provide a little tougher layer so that it does not, over time, work thru the insulation/shrink tubing to the case. The paper that was typically used as the original covering you describe is called fish-paper www.ebay.com/itm/122685484714?hash=item1c909feeaa:g:9eMAAOSwPhdVQ9pB
I have no idea how it got that name but you could consider getting some if you want to add that extra layer of voltage and physical insulation or maybe just use thin cardboard ??
There is all kinds of good insulating material on Ebay. Here is another mica insulation www.ebay.com/itm/124766763516?hash=item1d0cadb9fc:g:gJ0AAOSwq~xf5KvQ
of course, the mica sheets might not bend and conform very well. For truly high voltage wiring off transformer leads, I have had to use meter lead wire also. Meter lead wire is supposed to be good to a few KV insulation. For really high voltage wiring in a cabinet I use copper core spark plug wire.
www.ebay.com/itm/224285678435?hash=item343877db63:g:aDAAAOSw8-Rf3lJY:sc:ShippingMethodStandard!79903!US!-1
www.ebay.com/itm/164802252713?hash=item265efacfa9:g:nYsAAOSw2MdfAd9T
These links are just for thoughts and you probably want to shop around for the best prices. I recently bought the USA made copper core spark plug wire in a 100 foot roll for about 40 cents per foot. Hope this helps.
Great video sir!Thank you very much! I have a question.My amp is 5watt champ with 4ohm secmndary. What happens when I connect 8ohm speaker to it.The primary is has to be 8kohm.So connecting the 8 ohm speaker I'm actualy rising the primary impedance witch shoud lower my output power?What more goes wrong?:)Does the 6v6 start working beyond his limiths?
Thank you very much!
love watching your videos... question... Mcintosh MC75 uses 2 kt88, but they are able to make the Zout to 600 Ohms..how can i make the same dual kt88 to have 1500 ohm zout? pls help... thanx a million...
Thank you. The output transformer has to have a secondary winding equal to 1500 ohms to have that Z output impedance. 1500 ohms is not a common value and for testing, you could try the 600 ohm connection and it should work. You may not be able to get full power output but it should work reasonably well.
Here is the schematic for the MC75 where you can see the 500/600 ohm output is located on the output octal socket and taken from the cathode winding. Generally 500 and 600 ohm outputs are interchangeable and may be stated either way as they are close enough to each other.
www.thetubestore.com/lib/thetubestore/schematics/McIntosh/McIntosh-MC75-Service-Manual-with-Schematic.pdf
Hi you, cool channel! Let me first say that I know nothing about electricity or how to build an amp, in future I'll get some techman to recreate an old '66 Marshall JTM45/100 (like the ones used by Hendrix at Monterey or Angus Young in the High-Voltage AC/DC album where he used a 675 Volt Marshall with KT66) by using vintage Partridge transformers instead Drake's. I always seen those Partridges going matched with EL34s. But now I'm wondering if '70s Partridge transformers (those ones used in Hiwatt DR103 amps) could match four KT66 tubes and their high-voltage stuff. Thanks
Thank you for a great and simple video. Are those calculations for both triodes SE and pentodes SE? I find it hard to understand, for example if that load resistance in the tube data sheet would be the same as transformer primary impedance - it would be perfect match, right? But when you take 12AU7 as a power tube for 1W "Micro Champ" built - which has approx 7.7k load resistance, it needs 25k primary.. Why?
There’s a difference between “Plate Resistance “ and “Recommended Plate Load Resistance” in tube manuals. For single ended triode amps the typical load resistance is 2-3 times the plate resistance. There’s no equivalent “rule of thumb “ that I’m aware of for pentodes..
Great video! Thanks. I like using old military tubes but sometimes have difficulty finding to A impedance or A - A. Do you know of any books/info that would help with this? Thanks.
I found all the books difficult in my education in the 1960's. Once a fairly advanced understanding is achieved, it becomes much easier to see what the writer was trying to express. There is good stuff on the Internet but there is also a lot of error so be careful. Probably the best source would be Amateur Radio Handbooks from the 1960's and 1970 time frame for discussion of tube fundamentals.
Great! I love practical examples of the theory.
I love the antique analog multimeter ! whats the brand / model please?
I believe it's a Triplett model 630-NA.
@@kstlfido Thanks for the info !
Thanks . Excellent tips!
Excellent stuff..thanks EPT
Hey Dave, my 1st post with you. Like Uncle Doug, I think your sharing these videos with the public is great! I'm sure you will help a guy like me to build my own tube amp. Safety is always the #1 consideration when working around the high volts in a tube amp. I have a question; if using a pair of 6L6s in push pull, and using the data sheet for a 6L6 and finding that it needs 6600 ohms of impedance from the primary of an OPT, do you need an OPT with a primary impedance of 6600 across the primary or from center tap to either lead, and how come the OPTs that I've looked at for replacement for output stages that have 6L6s are 4000-4500 ohms of impedance? Is there calculation you need to come to the correct impedance match for the 6L6s and the primary of the OPT? I feel stupid because I can't understand this. Thanks
Hi Hubert - thank you for your kind words. First, the impedance is from plate to plate across the complete primary. Secondly, your question about how the pros using primary impedances well below the RCA tube manual has baffled all of for decades. For the small 6V6 or 6AQ5 level amps, the tube manual seems to hold true and I recommend it. If you read articles on McIntosh amps, you will see that the primary Z of their transformers are as low as 1000 ohms. But then they also have windings that the cathodes are connected to - very complicated. I have personally found that all the pro amp makers seem to cheat the tube manuals in using primary Z both lower and higher than recommended. If you ask this question to an academic, they will simply spout out to you what the books say in the form of a maximum power transfer theorem - and they will be wrong. I have personally found from building amplifiers that the primary Z lower than recommended usually provides improvement (higher power output and lower THD) over the tube manuals recommendations. So, I haven't been much help at all. Maybe you can get a copy of, "Audio Cyclopedia" by Howard M Tremaine. It is an interesting book to go to bed with.
One thing about output transformer is the impendence rating are usually determined buy testing them at a set frequency like 400 cps. The output transformer is also an inductor driving an inductor (the speaker voice coil) as the frequency changes you will find the impendence on the primary of the output transformer will also change. Amp companies try a number of different transformer and then go with the one that works best for their amp/speaker combination. Hopes this helps.
Hi, LordKelvin100 - I think you have some really interesting questions and I will do the best I can to give you the information that I have as I understand it. Obviously, I do not know everything about vacuum tubes but I am always willing to share what I do know.
I believe the best answer I have to your first question is, tube designers, in the beginning, simply did the math and gave us the theoretical values for maximum transfer of power theorem. Here is one reference:
en.wikipedia.org/wiki/Maximum_power_transfer_theorem
However, quality improvements in fidelity made it necessary to deviate from this method so, in the design of modern low distortion amplifiers, efficiency was sacrificed for fidelity.
As for Class A vacuum tube amplifiers, the stated parameters there are simply that plate current flow for the entire cycle and it can be single ended or push-pull. We also have to remember that in the design of vacuum tube amplifiers as seen from RCA tube manuals, efficiency, and to some extent, fidelity, was paramount and the creative process of “crunch”, and “over drive”, and the such that the musician requires in the creation of music was not part of the vacuum tube design formula. I only add this comment for those that are interested in “the sound” rather than the purely analytical design as these two philosophies don’t coexist.
As for Class AB (AB1 and AB2), the tube manuals will tell you that Class AB1 says that we are willing to drive the grid of the tube right to the point of grid current but we won’t cross that line-in-the-sand. This will give us a little more power output and increase our efficiency and allow us to advertise our amp at a higher level of power. Class AB2 says we will cross that line-in-the-sand and draw a small amount of grid current on peaks so, once again, increase our power at a little bit more distortion. I believe in reality, we have crossed the line into sales philosophy.
As for Class B amplifiers, these amplifiers are designed and biased and the proper tubes are used for this purpose such that only one tube conducts at a time. Examples of good Class B tubes are the 811A and 3-400Z triodes. This increases efficiency and notch distortion and is primarily used in amplitude modulated (AM) radio stations. The increase in distortion is acceptable and the increase in power output and efficiency is worth the increased level of distortion.
We also have to remember that the Receiving Tube class of vacuum tubes that we usually deal with are not designed for Class B or Class C service. They are designed to operate in the Class A, AB1 and AB2 class.
There are a few basic designs that come to mind in vacuum tube audio amplifiers. The Williamson, Mullard, Dyncao and McIntosh. Some of these differences are primarily paraphrase vs long-tail inverter design and pentode vs triode. The McIntosh design is the most interesting and has a plate load Z of 1K ohms and a cathode load Z of 1K ohms. A beautiful design but cannot be duplicated without the McIntosh output transformer. Best article I have ever seen on the McIntosh design is in, Audio Cyclopedia, by Howard Tremain.
I think your comment on hollow state design by formula is exactly right and is what I have tried to express and have experienced. We don’t disregard these approaches but modifying them by empirical design is why we are where we are today in the reality of vacuum tube circuits.
The Recommended Plate Load Resistance is typically quoted for a given distortion value. Tube manuals most often use 5%.
Hi Dave, I have a question about 2 output transformers I have and if they will work in a single ended application. I took them off of a pair of 10" speakers out of a 1966 JVC radio, reel to reel tape, radio console. The unit said Stereo, each transformer on one side has a common, 4 ohm an 8 ohm lead. The primary side has 3 wires, it says 5K and the middle wire is a Center Tap. Could I use them in a single ended amp with a 6V6 or 6AQ5 if I didn't use the center tap? Or will it not work? Im not sure what the center tap is for. Thanks, Tom
+Bucyrus Erie12 The center tap is connected to the power supply. The other two wires that connect to your output tubes are likely blue and brown. You will get audio output if you use it with one tube but the power level will be low and the low frequency response will suffer the most. The sum current through a PP transformer is basically zero so there is no saturation of the core. In a SE amplifier, the tube is run class A so there is constant current through the OPT and it takes amazing little DC current to reduce the effective inductance of the OPT to just a few millihenries. I would use it as a PP amplifier OPT and it will perform properly.
The best video so far!!
I tested my 1959 gibsonette GA-9 O coil using a similar technique and arrived at 27.5:1
With the stock speaker at 3.5OHMS
Z= 756.25 OHMS 27.5 ^ 2
so P = 2647OHMS Z * 3.5
I cant find within the data sheets how this single ended dual 6V6 class A should be. The closest I saw was a triode config at 1960 OHMS
I know what you mean. Often times these impedance's are not what tube manuals call for. Not sure if you have ever run across the Fender amp that has a 1 ohm load. I think it is the "tweed" version of yesteryear. I don't remember all these instruments perfectly some times but I do remember it has four, 4 ohm speakers parallel. It runs a pair of 6L6's and will indeed put 50 watts into a 1 ohm load (7 volts RMS across a 1 ohm load). I had more than one "double take" the first time I ran across that amp. Also, 1960 ohms and 2647 ohms are not That far apart... :-) and maybe they did it on purpose (mismatch) for the tone quality... Who knows???
I have made quite a few transformer Z measurements, both voltage ratio and direct impedance bridge measurements and while the voltage ratio and Z bridge will compare pretty close, they hardly ever are exactly what the transformer manufacturer says the transformer is. Mostly, I would say, that everything is within about 5% and within the world of transformers that is pretty close.
This is my foray into guitar AMP as opposed to HI-FI with tight tolerances to limit THD. I read further that a 6V6 at 320V on the plate has an expected THD of 12% @ 5.5W. Considering I dont allow my dynaco equipment to pass > 1% until 30K, I find it kinda laughable.
I understand the crazy THD figures the manuals give. I am sure that is with no NFB or any enhancements like ultra-linear and everything else. We know the tubes will do a lot better than that.
I did not start into guitar amps until I retired in 2010 and all of my experience was with HiFi just like yours.
Well, the guitar amp is a whole different world. A "music creation" amp with 0.1% THD will never be accepted by the musicians. The harmonic profile of guitar amps is horrible and THD at rated power is never less than 10%.
These little SE guitar amps from the 1950's have a triangular harmonic profile and everybody wants one just like them. You can practically throw all your HiFi experience out the window when it comes to guitar amplifiers.
So i get it.... Acoustics have their own harmonic characteristics, based on design and the type of wood used, and electric guitars require amps to produce distinct harmonics based on circuitry. I just finished an ST70 that ive tested on the HP331A averagingway below 1%, were gonna print it down to the guitar shop and plug it into two speaker cabinets. I wont bridge an ST70 because the monoblock performance is quite bad.
I was wondering whether it wouldn't be safer to avoid the variac/6V TX altogether and use an oscillator like your SG502 or SG505 on 50/60Hz as the voltage source. Is there something against that that says it won't work or is a bad idea? You can get about 5V out of them. I did this once to figure out the secondary phasing on a PTX and it seemed to work OK.
QuadMaestro I agree with you, it would be safer and pretty much any audio oscillator should work. The Z of the oscillator is high so the amount of current would be limited to very small amounts. I was a little reluctant to make this video as connecting the source voltage to the low voltage winding could easily produce HV on the secondary side. Thanks for your suggestion
Question: If you apply voltage to the primary side via the 6V transformer/Variac, why not to put 4 or 8 ohm load in the secondary side and then take the volt reading thru that load?
+Ramon Medina You could do that but it wouldn't change your reading. Putting a 4 or 8 ohm resistor in series with the secondary and then your meter across the resistor-secondary series circuit would only add the 4 or 8 ohms to the internal impedance of the meter which is probably 10 megohms or higher. Hope this makes sense. You would end up with the same reading even if the resistor were several thousand ohms.
Thank you,, great video 💡❤️
Fantastic practical video!!!!
How do you determine impedance ratios of small signal mic input or mixer output transformers? I’ve done it for unknown outputs that are used in tube guitar amps. Same way?
It would be done the same way but care should be taken when measuring these small transformers. Many have a rating of zero DC current thru their windings as there are thousands of turns of very tiny wire and I am sure could be permanently damaged by applying more than a mA (or less), of current thru the windings. I don't know this for a fact but I would suspect even a vintage VOM could saturate the cores of these transformers. Modern day digital meters are high Z and the voltage output to measure things like resistance is much smaller than the older ones that used dry cell batteries for the ohm meters and was a simple meter, resistor and battery circuit.
With this said, I have been unable to measure some very sensitive (i.e., 20 uA) meter movement resistance values with high-end digital volt meters as their "computer" seems to "hunt" for some level of current that they can not obtain and end up giving false readings.
Transformers around 100 years ago were a passive way of raising voltage as long as the load impedance was very high, well into the megohms. Manual labor and material was surely cheaper than vacuum tubes and the components used to build active amplifier stages back then.
I would start by putting a very small AC voltage (100 mV?) in series with a 1 megohm resistor into the windings of one of these vintage microphone transformers to make sure current is very limited. You may have to tinker with that value of resistor somewhat and use your most sensitive and high Z volt meter to measure the input and (unloaded) output voltages of the transformer under test. If you can safely and accurately get that voltage ratio, then you square it and get the impedance ratio. Hope this helps and works for you. Just my thoughts on an approach at the moment.
hi i've being looking on the net about how to choose the right PT for instance like with caps to use for the power section and soforth any help would be much appreciated
This is a great video!
What was the need for the 6v transformer? It was the only boy that I don't understand. Is it necessary or can you run 9v from the Variac?
It is just an extra step is safety so no matter how high one might accidently set the Variac, the voltage will be low and safe everywhere on both sides of the transformers. An example is measuring a voltage step-up of 0.1 VAC to 10 VAC is a (turns and voltage) ratio of 1:100 step-up which is the same as a 10 VAC to 1000 VAC ratio. My philosophy is, first thing is to stay alive and the second is not burn up the tubes... 🙂
@@ElPasoTubeAmps amazing! Thank you, That's a very helpful and fast response :)
if you don't know which of the 3 wires on the primary side is the center tap. how do you determine which it is? thanks.
It is usually a different color from the two "outside" wires of the HV secondary. Often times the HV wires are red and the center tap is red-yellow. Also, the DC resistance as read with a normal ohm meter will be approx 1/2 the value across the whole secondary and will be the same from the CT to each side of the secondary
Thank you very much for the great videos. I'm just starting out.
Good work, neighbor.
Joseph - we've got to get together sometime. WA4QGA and I am in QRZ.
“I got more transformers than the law allows”... had me laughing
That is an old Southern saying I probably heard from my grandmother. She was born in 1896 and my grandfather in 1892. That is where many of my root philosophies come from as they were the ones that raised me. I got plenty more sayins' like that.
Probably learned good solid morals and values from them too!
Also the RPN calculator was a treat
I NEED YOUR ADVICE, I just bought a brand new BUGERA V22 HD amp. The guitar I used is an EPIPHONE LP "56 ReIssue with P-90 pickups. As I move around the room there is a HUMMM that goes from non-existent to very loud. Then I recently read an article about UNSHEILDED PICKUPS and how they can cause havoc on tone and signal interference. The finish and materials used on the body of this CHINA MADE LP guitar is really nice BUT we all know that Epiphone electronics is the worst. QUESTIONS - 1) Is it the guitar causing the different humms as I walk around the amp? 2) IF I wanted to change the PUPS would Mini Humbuckers FIT where the P-90's are so I would Not have to resize the PUP cavity? Thanks In Advance, Ade
that's 60 cycle hum that you're getting. its very normal. but can be intensified by a lot of different things. some things to check to try to reduce it are, is your amp plugged directly into a grounded socket in the wall? don't plug your amp into a surge bar or anything like that, it can/will make interference noise worse. are your pickup/control cavities shielded? if not, it wouldn't be a bad idea to shield them. if your pickups aren't "microphonic" then theres not really much that can be done about them as far as 60 cycle hum is concerned aside from grounding/shielding them better. is your cable a shielded cable or not? are you near electronics where you're playing (Tv's, stereos, anything with a transformer, and fluorescent lights can be the worst)? essentially, p90s are large single coil pickups, and single coils have a lot more hum by nature than humbuckers, humbuckers are called that because that's exactly what they do, they're 2 single coils wired opposite to cancle/reduce hum. I wouldn't damn the pickups per se, if they sound good to you and do what they're supposed to, theres no reason to ditch them. general the hum you're describing is from outside sources or improper grounding/shielding.
+a. webb - P-90s are single coil pickups so they will pickup and reproduce hum created by various fixtures but commonly the most powerful and close at hand is your power transformer in your amp. Shielding can reduce it some but because of oscillating magnetic fields of such power some hum will get reproduced by a single coil pickup.
This is exactly why Seth Lover invented Humbucking-TM pickups which are dual coil where magnetically one coil is out of phase by 180 degrees so the hum in one coil will subtract from the hum in the other. If they are well matched the hum will be close to zero, but you also lose some of the brightness in the response to your guitar' strings. This is why a stock Telecaster or Stratocaster sounds brighter than say a Les Paul with Humbuckers.
It is a tradeoff and only you can decide if the greater brightness is worth either the hum or the complexity of paying attention to where you stand or applying devices like compressors or noise gates.
which Kindle of Power transformer could i use as audio output instead a specifc one on an El34 tube: half bridge, full bridge...?
Look at it this way - suppose you have a 200 VCT secondary and a 6 volt filament winding. That gives you a turns (or voltage) ratio of 200/6 = 33.33. Now square 33.33 and get an impedance ratio of 1111.11. Now if you put an 8 ohm load on the six volt winding you will get a reflected impedance back to the 200 VCT winding of 1111.11 x 8 = 8888.89 ohms or about 9000 ohms. if there are other windings on the transformer like a 120 volt winding and a 5 volt winding, just tape them off and ignore them - do not short them together... With this procedure in mind you will have to do some experimenting. This 60 Hz power transformer is not going to be a high-end HiFii transformer but it will produce audio. Hope this helps.
thanks a lot for this information. :) Anyway I have another doubts about these Transformers and I would like to know If you could help me via PM
Thanks
you can use a Kindle Paperwhite for a good 111Kiloohm into 1,21gogowatt power for the flux condensor
i have a 213 magnatone out put sound almost 0 and i see light in all the tubes i think the output tubes look dimmer than the rest could you point me in what direction i should go to repair this.
Thanks a lot for the video, much appreciated. Take care.
Hi EIPaso TubesAmps I have a question that may sound silly. What is the difference between HiFi power transformers and Guitar tube amp PTF. While on that is there a difference between solid state PTF's and tube PTF? Thanks love to hear the answer :)
For vacuum tube power transformers, there would be no significant difference between HiFi power transformers and guitar amp power transformers. They both supply in the neighborhood of 450 volts DC to the plate of the tube and often times they have a separate winding or a tap on the HV secondary to derive a negative bias voltage for the grids of the output tubes. HiFi transformers may be potted for a nicer appearance but what is inside is the same in both cases. As for output transformers there is considerable difference as the HiFi output transformer should have a much wider frequency response than the guitar amp output transformer. I assume PTF is power transformer... if so, the difference will be voltage level. A typical 50 watt tube amp transformer might be 800 VCT at 200 mA whereas a solid state power transformer might be 80 volts at 2 amps. In each of these cases, that would be 160 volt-amps or approximately 160 watts. Hope this helps.
ElPaso TubeAmps frequency response that a amplifier plays has not a thing to do with what transformer you use. If you have a amp that both use the same tubes or transistors but one is a sub amp for low frequency say 40-80 HZ and the other covers 20-20,000hz the same transformer will run both amps.
nice ! , without hollywood "experience", nice presentation about transformers and the way you can deal with,
Hi and thanks for the vid!My problem: can I replace the 2 output transformers of my integrated amp Bell 2420 in order to upgrade the sound?...Marked on them : impedance Pri :9500ohms CT, Sec: 16 ohms Tap ,8 ohms ,4 ohms.Many thanks
That is a tough question - the answer could be, "yes" if and only if, you could find an output transformer with better specs than the one in it now. The problem is, you probably cannot. The ultimate output transformers for PP 6L6's and the such are still made by McIntosh with their unique and patented design. I think the sane thing to do is experiment with different tubes. Changing the output transformer is like changing the compression ratio and cam timing on a car engine (and having the machine shop to fabricate these items...) It is just pretty much beyond all of us at the OPT level - nothing more than a random blind swapping with no repeatable way to confirm performance - I don't mean to be discouraging but many things are just what-they-are and true fundamental changes are not possible for us experimenters - hope this helps.
Yes, it does!thanks a lot!
My question is how can you determine the amps a transformer can handle. How much 6.3 vac amps, how many high voltage MA?
It is actually fairly simple to get a good ball-park rating on a transformer but it is hard to put into just a few words. Transformers are rated in volt-amps (VA) which is AC volts multiplied by AC amps (RMS values of both) this gives what is called "apparent power" but for all practical purposes for the small transformers that we use, the VA rating the power rating (in watts) is the same. Try to keep things simple.
As mentioned in this video, first look carefully at all the data written on the transformer. It it does not have specific ratings on it, maybe an Internet search on a manufacturer and part number will give you some good information. If you know the equipment it came out of, you may be able to determine something about the transformer from that data.
I want to be careful not to mislead you and give you information that is not reliable but here is some data to think about. I am considering a UTC CG-301 transformer. It weighs 15.5 pounds and is rated at 200 watts. See the attached UTC transformer catalog, page 47. You could, for ball park values, use this as a model. In other words a transformer weighing half that weight (about 7.5 pounds) would be good for about 100 watts and so on. It is a place to start. After this information, you will have to do Ohm's law equations using voltage and current and power to determine the unknown value you need.
Also, be very careful with transformers. They are no more dangerous than a rock when unplugged but when plugged in, HV from transformers can be death-on-contact.
For a practical example, lets assume a transformer of about 7 pounds (100 watts) which has a 6.3 volt 3 amp, a 5 volt 3A, and a 600 volt HV secondary that you do not know the current of. The 6.3 volts at 3 amps is 19 watts, the 5 volt 3 amp is 15 watts so you have about 65 watts left for your HV winding. I = W/E so this gives I = 65/600 = 0.110 or about 110 mA. This should be a pretty conservative rating.
Hope this helps.
UTC catalog vk1nam.wordpress.com/yaesu-ft-857d-menu-settings/
Nice info!
i have a question based on your comment of more amps than the law allows and that is could you tell me what the wires are on a K70749 power transformer that came out of a conn minuet 541 organ? i figure the 2 black are primary, and i also figure the green wires are 6.3v and the green/yellow stripe wire is the ct for the 6.3v. the wires i dont have a clue of and need help id with are the following: 2 ) wires are either orange or brown cant really tell but they are twisted together, next are a red and red/green striped ( also twisted together), a yellow and yellow red stripe ( which are twisted together) and lastly is a blue wire. i have been looking all over the net and i have not been able to find anything.
+lordraptor11 I don't think you are likely to find that exact transformer anywhere on the Internet but you are better than half way there already. I, too, would bet the black wires are the primary so I would (carefully, maybe with a 100 watt light bulb in series with the winding if you don't have a Variac) connect it to an AC power cord and with a voltmeter capable of measuring 2000 volts or more, probably not a modern day digital meter, start measuring the red, yellow/red stripe, etc wires and drawing out the schematic. It's not that hard and I suspect between the red/red you will get 800 to 1000 volts or more with the red/yellow the CT, etc. I have no idea what the blue wire would be but you will find out with careful measurement - possibly a 120 volt, or so, tap for a bias supply (?) Be careful, 1000 volts can be very nasty and even deadly.
Hi Dave, As usual, I always enjoy your videos..I agree with you 100% about over emphasizing safety while working transformers. Just because the transformer is sitting on the bench and outside of an amp, makes it no less dangerous. Even those who have been in the biz for decades need to always be mindful that one stupid mistake could be your last..
I don't want my epitaph to read,' Here lies a guy who was so stupid that he electrocuted himself even when he knew better...LOL.
Better to read, " Here lies a guy who died of a heart attack AFTER making love to his wife on his 104th birthday. If only he had stopped after the 5th time that morning....LOL Well, if you are going to dream, lets do it RIGHT!!!!!!
Glenn - you sure got it right... my motto is, “Live like a rock star and die quickly” (but not with HV,,,) As much of a pain as I can be to the family, I don't want them to find me next morning still sizzling on 3 KV which, if they touch me, they just might be meeting me Upstairs.
I really have a lot of fun with YT and have met a great bunch of guys. Always enjoy hearing from you. Ohh... and just in case if we don’t die after five times with our wives then maybe just four times in a menage a trois with ladies half our age and preferably a heart attack and not shot by jealous boyfriends :-))
so if i am winding a transformer and i want say 6000 ohm primary to 6 ohm speaker how do i know the minimum turns on secondary. i understand the ratio and impediance but you never see a one turn winding, its always multiples
Do you troubleshoot small 50 watt amps Ive got a pair which are identical builds but do not pass sound I think its jumper related or something's fried the OT on both but I dont think thats it I think im missing jumpers. I get voltages and close readings but no sound. Near Dsllas area... thanks.
I don't take in equipment anymore. Just too much to receive and reship and I have become unreliable. I would like to help you but it is difficult to do over text even though, as you say, it may just be a jumper problem. Can you "Google" the manual for the amplifiers?
Do you repair transforms? I have a large power transformer that feed large 1000watt power amp and pre amp on jukebox unfortunately evertime I connect power supply to it it kicks breaker on power supply. The transformer doesn't smell burnt and sure looks fine. This transformer has many wires and hard to find another is it possible to rebuild or should I just use three separate tranformer instead of one large.
Thanks
I do not repair transformers. However, let me tell you a quick story. I have a Collins power supply for the S-Line equipment that is about 2000 volts CT and feeds a 5R4 rectifier. This power supply has given me trouble two times ( I have made two videos of it) and each time the transformer appeared shorted but as with yours, never smelled bad. The problem was, the thin insulation on the 2000 volt secondary winding was arcing between the wires (not go ground). Do a very close visual inspection of your problem and you may find a similar problem. To finally solve my problem, I cut the secondary wires off as far down into the transformer as I could safely and still have room for connection and then extended these wires with high voltage meter lead wire and extra shrink tubing insulation at the connections. It worked. Also, you may simply have an external short that you have not noticed yet. You may have to disconnect all of the secondary wires from the transformer to determine if it is indeed a bad transformer or an external short on one or more of the secondaries. Hope this helps..
Can i ask you something? First of all thanks for video. I have 6 output transformers that was in televisions with pcl86 tubes. I wish to biuld amplifier but all schematics i find use 5k primary. When i check mine its 350-450 ohms primary but i remove thdm from working televisions. Can i use 350 ohms primary and be safe?? I mean its supose be 5k or its normal to be 350 ohms? I dont believe 6 are bad because i remove them working. Thanks
You are measuring DC resistance instead of AC impedance. The first thing to know is are your transformers made for a single output tube or two tubes in push-pull. A very common value is 5K impedance from one plate lead to the other plate lead for two tubes in push pull.
Transformers made for one output tube, like a 6AQ5, 6BQ5/EL84, 6V6 or 6L6 are pretty high impedance like 8K or 10K but push-pull transformers are more in the 5K to 8K range. Absolute optimum impedance is nice but often times not realised with what we may find in old equipment but even if the impedance is off somewhat, it will still work OK.
Old output transformers if they are push pull (made for two output tubes) often time have a blue wire for one tube, a brown wire for the other tube and a red wire for the center tap (CT) that goes to the power supply high voltage, on one side of the transformer and maybe a black and green wire on the other side of the transformer for the speaker connection. Single ended transformers (made for only one output tube) will likely have two wires on one side for the tube (the 350 ohm winding as you found) and the other side will likely measure almost like a short circuit as it is made for 4 ohms impedance (not to be measured with an ohm meter). My guess is your transformers are for one tube and should work with any of the smaller tubes like the PCL86 tube. Once you figure out if your transformers are single-ended or push-pull I may be able to help you further. Hope this helps.
Thanks alot. I understand you my friend. It is for single ended. So how supose i can check ac impedance?
@@jonathangauci2182 Here is one of my videos that may drive you crazy or you may like it -
th-cam.com/video/CJ__UfPMG2Q/w-d-xo.html
On the other hand, you can buy an impedance meter like the MS5308 LCR tester as I show in this video which makes it much simpler.
th-cam.com/video/HV_6gmaZDF8/w-d-xo.html
Thanks alott
You've got the same calculator and clipboard as Alan Wolke :)