Hello David, glad to see a new video from you. Really enjoyed you discussing your thoughts on circuit designs while having the schematics in hand. I am absolutely going to download the 4 volumes of 100 amplifiers by Lilienthal Engineering. They look beautiful thank you for mentioning them, I had no idea about them, or that they were available for free. Your redesigned KT88 amp is stunning, truly, you do such neat work, it's something I'm going to try to emulate, and the performance speaks for itself. I just wanted to mention that I make solid state rectifiers using the bases of worn out or broken octal sockets and a pair of 1N5408 diodes (like the 1N4007 but rated at 3 amps) costs about 7 bucks for 50 diodes, so it's really only the time it takes to solder them in place..all of 5 min. Looking forward to a video on that 1948 push-pull James Millen amplifier, another great looking unit and a great piece of history. Hope all is well with you, and as always, work safe.. Take care, Tom
i just built a kt88 williamson. I usually copy the w5m schematic and make some changes to get the right voltages. But it's funny to see that you do it the same way. I also leave out the stabalizing things if i don't need them. I did go back to 12au7s in the preamp part though. great vid! thanks!
Honestly, the 12AU7s are probably a better way to go and that is what I used to use but the 6SN7s with that octal socket are easier to wire. No doubt I have many more good 12AU7s than 6SN7s but I seem to stick with the latter. Thanks for your comments.
Nice messuring Elpaso I'm a diy highend audio tubeamp builder. My setup is ecc83 first tube, fase inverter the 6sn7 and power amped by 6550. Handmade output transformers on old school winding machines. Designe doesn't need nfb at all. Maybe you want to view my schematic, I'm curious about your ideas about it. Well I'll view some more if I get the time. Again nice shag with good messuring equipment.
I built that Williamson circuit, I just gave the output it's own negative supply. and you can bias all of the output tubes individually. I Also doubled the circuit for stereo, I get about 50W per channel 6l6 pp
The Genelex KT88's are great (use them in my tube amps). Keeping the cathode current down to 70 ma increases tube life (this is an issue). It would be interesting to try KT120's KT160's.
Gwenyth Paltrow makes an adhesive for amplifier power supplies? Who'd have guessed? Wonder if any of her colonics are good for cleaning out noisy pots? ...Thanks for another good video.
That is good to know. Thanks... I have found that the red glyptal insulating varnish is getting hard to come by. I don't need it often but it does come in handy sometimes.
The power transformers from guitar amplifiers would be great. The output transformers (OPT) from guitar amplifiers do not have the same frequency range as a really "high-end" OPT and I suppose the most discerning ear (whatever that means) from an audiophile (whatever that means) might hear the difference in fidelity between the two types of OPTs. There is obviously more to an amplifier than the output transformer but at the amplifier's highest rated power limit, it will make a significant difference in total distortion between a high quality reproduction amplifier (i.e. HiFi or stereo amplifier) than a musical creation amplifier. i.e. guitar amplifier. We want distortion, overdrive, crunch, etc in the musical creation amplifier (the guitar amp) but we want the HiFi amp to playback what was created in a "perfect" manner. With that said, all vacuum tube amplifiers have more artifacts that are created by the amplifier, which we think we are supposed to not have. I have believed for a long time that we somehow enjoy these artifacts created in the playback amplifiers which adds to the musical enjoyment. Otherwise, why would we still be so stricken and enamored with vacuum tube amplifiers when even a cheap solid state amplifier is likely to outperform virtually any tube amp in lab tests?
From the data sheet it can be seen that the DC voltage maximum is around 500 volts and the current is 250 mA. That is 125 watts so it should easily power a 50-60 watt amplifier considering that amplifiers should be seen as about 50% efficient. These are good safe ways of thinking about issues like this. Of course you could push it a bit harder and likely be OK. That is actually pretty tough for a tube that size but what makes it possible is the voltage drop across the tube is low (something like 15 volts for MV rectifiers) so the tube does not run terribly hot.
I think those are 1623 tubes in that amp. And if you need one I have a Raytheon rk-11. It is the same tube. I also have an RCA 811 both are really good if you could use them.
Thank you very much for your offer of the 811s. I remembered right after the video that the tubes are 812 tubes and not 811. Had one of those "senior moments" making the video. I have the two in the video and two spares. I really do want to get going on that amplifier and get it on the air.
I thought you got a date wrong in the title at first. You need to look in an amp that I'm working on right now. The McIntosh 50w-2. One of Mcs earliest. Very unconventional. Separate amp and power supply. The chassis's are actually the transformers. They probably weigh 40 lbs a piece. They have two 5U4s. 12ax7, 2-6j5s driving 6L6s. Driver coupling transformer. They are linear from like 5hz to 100khz . I feel privileged just working on them. Can't wait to test and hear them.
Yes, 2020 seems like "back to the future" to me... Wow... I would love to deal with one of the old McIntosh 50W amplifiers. I have seen a lot of them in pictures but never in the flesh. I think Paul Klipsch said, what the world needs is a Good 5 watt amplifier and Frank McIntosh said, what the world needs is a Good 50 watt amplifier. Looks like they both were very successful.
The plate resistor in a quad configuration allows for current sharing across the paralleled tubes. Look at any high power solid state amplifier or high current linear regulated power supply. The multiple power transistors always have like 0.22 ohm or similar value emitter resistors. Same reason, current sharing. Now I have noticed many OEM quad tube designs of the 60s didn't do this. They just put the plates in parallel. I guess the tube quality of that era ensured highly matched sets. You won't see level of consistency that with today's modern tubes from China and Russia.
Andy, good point about the resistors. I remember the fractional ohm resistors very well in the SS amps. I just figure each active device needs a little "space" of its own, so to speak. It definitely seemed to work well in the UTC W-20 amplifier and it made a whale of a difference in the quad 1625 modulator I built. I am actually convinced from my own experience, if we buy top-shelf vacuum tubes of today, primarily the ones made in Russia, I think they are as good as the USA tubes of yesteryear. I know that some are re-branded, same as always, and the premium tubes of today seem to be nice and strong, well balanced, and they keep their balance. That has been my experience with the re-branded JJ tubes sold by Telefunken and I am thinking particularly of the KT88's. Thanks for your input. Stay safe.
@@thomjmoore Indeed... I love astronomy. I recently purchased a Sony 200-600mm lens that I was out imaging the moon tonight. Just below freezing here so the humidity was down. Pretty amazing what we can do with a camera lens nowadays. I also have recently purchased the iOptron Star Tracker that works quite well and I hope to image some galaxies soon. I have a Meade 10" that I have used and made a number of nice photos with for the last few years. The camera lens won't do what a 10" scope will do but it sure is a lot easier to carry around. Here is one of my first attempts of moon videos that are unlisted on TH-cam. I now use a Sony mirrorless A7RIII camera that I am very pleased with. th-cam.com/video/P1255sjX9B8/w-d-xo.html
@@ElPasoTubeAmps That's impressive, I have an older Meade 8"..it's good, but doesn't get anywhere's near as clear as that 10". Did you use the A7RIII camera for that?
@@bucyruserie1211 Yes. the 40 Megapixels are amazing. I can blow it up the still pictures to the absolute max and no pixelation. I think you could do some very nice astrophotography with an 8" scope. A critical factor for a SCT is, the collimation must be pretty much perfect but don't turn any one screw on the front of your scope more than 1/2 turn each way. I turned one of mine too far and it came out of the threads and each screw has a spring behind it holding the secondary mirror. I had to remove the corrector plate and get it back together again. I learned the hard way. Now I have numbers on each screw with a dot of finger nail polish on the screw and the scope so I know exactly how much I am turning each screw when I make adjustments and how to get it back to a point where it was perfectly collimated at some point in time and for the conditions for that time. If the collimation is not perfect you get a big tail on stars called coma. When it is set up perfectly, your stars will be as sharp as NASA's. [sic] Coma is a spherical aberration from rays that come in off-axis. Coma shows up as little off-axis comet-shaped blobs that point inwards towards the center of the field and get bigger as you look towards the edge of the field of view.
Thanks for another very informative video. The 1.5H 500ma choke you use, is that the 159V Hammond from Mouser? Would this choke be a good one to replace the original in a Dynaco ST-70? 73 de KI6DGU
If I remember correctly, it is the 159V but I think it is too large to fit under the chassis of the ST-70. There is one a bit smaller (1H @ 300 mA) that is the 158T that might be a better physical fit. Don't take my word for it without careful measurement of the dimensions on your own. I bought two of each of these chokes from Mouser but have not used the 300mA chokes yet. 73 WA4QGA
@@ElPasoTubeAmps thanks for reminding me about the size; the original C-354 is a tiny thing. Even the 158T is too big, so the 158SA has the correct form factor. Dynakit sells a replacement which is shielded and is rated at 1.75 H and 200ma. The 158SA is 1.0H and 240ma. The original runs pretty warm, so I wonder if it might be better to have the higher current rating and lower inductance (fewer turns) of the 158SA for better reliability.
@@RandyHouk I agree with you. I would go with the higher current rating. 200 mA for the choke is absolute minimum rating as that is the idle current for a quad of EL34 so I consider that a bit under rated.
@@ElPasoTubeAmps I bought and installed a 158SA. It's resistance is 22 ohms lower than the stock C-354, so at 200mA it dissipates about 0.9 watt less. Runs MUCH cooler. I should also add that I replaced the 5AR4 with 1N4007 diodes and a 50 ohm 10W resistor to approximate the tube drop. I'm getting the same 415V at the plates of the 6CA7 outputs. The ST-70 sounds just fine! 73
I have found some transformers that claim to be less than 1 db flat within 10hz to 25khz at rated output at less than 1 percent distortion at 60watts they weigh about 15 pounds a piece the circuit also uses phase correction I do u understand that if the feedback phase is not basically out of phase with the output and becomes in phase it can result in positive feedback and causes all kinds of problems but perhaps the closer u get it to 180 out the more effective it can be and as it moves closer to in phase the less effective it becomes even if it doesn't cause problems just find it quite interesting and wanted to know what u think of this
I have seen those transformer advertisements also and I don't seem to be able to make all of them do what is claimed of them. Many of my amplifiers are built just to test such components as the OPT. Crazy, huh, that I go to that much trouble to test a transformer and see if it does what is advertised? As for phase shift, I am sure you are right about being frequency dependent and as the phase changes from + to - as it passes some frequency, no doubt it factors in to THD values. I have found it pretty amazing that I can get sufficient drive from the Williamson 6SN7 circuit to drive the KT88's to the level of 80 watts at a very respectful THD level. I find that pretty exceptional. I personally like the Williamson 6SN7 circuit. I have built it so many times and whatever comes out of the OPT into the 8 ohm load is usually dependent on the final stage and the OPT and not the driver stage. That may just be conjecture on my part but it is why I generally stick to the Williamson driver circuit.
@@raymondbeard8159 I agree these agree stated response is one thing but these are vintage early sixties transformers I will update on performance I think these might surprise I saw a cary amp that did pretty close to that with 6 six El 34 so it is possible but as far as the phase compensation on the feed back resistor this applies to Williamson designs as well in fact most of all them or infact any design that uses negative feedback I to agree and think maybe Williamson's design maybe tweaked slightly is the best design period
The red test jacks are connected to the cathodes of the output tubes (KT88's) so I can monitor the voltage across a one ohm resistor and adjust the cathode currents. There is a control at the top rear for bias level and then next to the left KT88 is a balance adjustment. I plug my positive voltmeter lead into the red jack and the ground into the silver (grounded) jack in the middle for each adjustment. You see them from the bottom starting at about 20:00
@@ElPasoTubeAmps Hi, sorry, what I meant was what type are they and where do you get them? Thx, btw. I enjoy your videos very much and I learn quite a lot as well.
@@rickmb6961 Here is one set on Ebay. They come in all colors. www.ebay.com/itm/4-Pcs-Blue-Insulated-Panel-Mount-Test-Lead-Pin-Jacks-Test-Points-w-Hardware/223716949507?hash=item341691be03:g:m1MAAOSw9w1bqEp4
Hey just a quick question. Maybe someone has asked this before but woulnt it be easier and more accurate to measure both cathodes at the same time and you balance the tubes with a null detector? Then you can adjust the balance easily without having to switch back and forth.
Yes, you can do that. You won't know the value of the cathode current but you can put one lead of your meter on one cathode and the other lead of your meter on the other cathode and adjust the balance for zero. That will work.
@@nuttyl283 No, not at all, the 6L6GC is a good sounding tube but can not deliver the power a KT88 can deliver. I listen to a stereo SET amplifier with 300B which deliver at most about 7 watts per channel and they sound wonderful and are plenty loud. All of the power tubes from the 6AQ5, 6BQ5/EL84, 6V6, 6L6, EL34, KT88/6550 are good sounding tubes. Nowadays there is the KT90 and KT120 which I have never heard the KT120 but I have built amplifiers with the KT90 and they are very good and provide lots of power. Got to remember that assuming starting with a 7 watt amplifier, it takes 70 watts to get twice as loud and then 700 watts to get twice as loud again. It gets pretty insane at that power level. From a 7 watt amplifier to a 100 watt amplifier, that is 11.55 dB. Decibels (dB) is the exponent ten (10) is raised to so, dB is not a very intuitive way of thinking of power and volume but it does allow us to express large changes in power easily. dB levels are always in reference to another level, usually power but it can also be voltage and current, and neither level can ever be zero. We call a level zero (0) dB as a reference level but it can never be zero power or voltage or current. The reason being is in the mathematical formula if you end up with zero in the numerator, the answer is always zero.... if a zero ends up in the denominator, the equation is in error, we can never have zero in the denominator or our calculator will return "error". Hope this makes sense and helps.
@@ElPasoTubeAmps Thank you very much my beloved teacher Mr. Elpaso. Actually I bought many tubes for resell but have very few knowledge about it. My Tube shops who sell me sell 45 2 tubes to me for resell. He said that 2 watts with my 90db speaker is enough 63-73db listening 2.3 meters away in small room. He also sell me many tubes due to he plan to closed shop. I have bought many tube such as 45 6SN7 6P15 E88CC 6L6GC. After I made 4P1SPP due to the cheapest tubes in my stock. I plant to build single end between 6L6GC and 45 to utilize a lot of 6SN7 I have. That is why I ask you schematic of 6SN7 drive 45 or 6L6GC in Single end. I am not sure which one is more suitable to my B&W 603S3 90db. I listen only 63-73db in small room. ttradio.net/the-push-pull-amp/ this is 6L6GC SE or ibb.co/3Sv4268 6SN7 45
@@nuttyl283 I can see you don't need a lot of power but with speakers of 90 dB SPL - that is at one watt, then 10 watts will give you 100 dB SPL, which isn't awful loud and you may appreciate the ability for it to reproduce low frequencies which require the most amount of power. You decide what is best for you but in my case, for my "back house" as I call it, I run my 300B SET amplifier, capable of around 7 watts per channel and my speakers are Tekton which they rate at 96 dB and life is good... and plenty loud. Too loud for my cats... Here is a link to those speakers and mine are even blue like the picture. tektondesign.com/product/full-range-speakers/full-towers/the-perfect-set/#color I looked at your two schematics linked in your email and certainly the SET is much simpler and may sound amazing - I have been building audio amplifiers for close to 60 years and until I recently built the SET 300B, there was no way anyone could tell me that it would sound so amazing. The low power SET amplifiers will certainly not perform on the test bench like a nicely designed and built push-pull amplifier and, I can't describe it but they sure "sound" good. I have measured amplifiers that are so perfect in performance but just sound dull. It's true. I have had McIntosh amplifiers for almost those 60 years I mentioned above and they are marvelous amplifiers in their performance and build quality and many can produce huge amounts of power that is very clean and easy to listen to. I have solid state and vacuum tube McIntosh amplifiers and love them for the reasons stated but again, at a loss of words, I really enjoy the SET. I might mention this - the 2A3 is a popular tube but it needs 2.5 volts for the filament - this is kind of nuts in my opinion. The 2A3 was replaced by the 6B4G and has a 6.3 volt filament and a "modern day" octal socket. Makes a lot more sense to me. Then there is the 300B a wonderful sounding tube. Needs 5 volts for the filament but that is much easier to come by. Just something to think about if you choose to use one of those. I am not familiar with the 45 but I see it also has a 2.5 volt filament... The most important thing in using a triode is for it to have a very low gain (mu) and I see that the 45 is very low so it will probably sound great. Keep at it. You will make it work and be pleased with it.
I agree with you since my hearing rolls off sharply above 8KHz but some people tell me they can hear (or sense or feel?) the second harmonic to 20KHz. My grandson (18) and my friend that is also my physical therapist can hear 17KHz and I don't doubt it. A 20HZ to 20KHz response with full power across that spectrum and THD under 0.5% is the goal and most McIntosh amplifiers (and your UTC W-20) do just that but some of my much-less-than-perfect amplifiers sound wonderful to me. Maybe it is kind of like homemade beer...
@ElPaso TubeAmps And of course harmonic distortion of a 14KHz tone starts at 28KHz for the second harmonic, which is totally benign, just a sweetener, and 42KHz for the third harmonic, which is not benign, but we are well into dog territory here.
@@EJP286CRSKW Honestly, some of my "lesser" performing amplifiers have sounded marvelous to me. I must like the artifacts of these amplifiers. However, very low distortion in the LF range is very important. This doesn't mean down-right terrible distortion at any point but something about those crisp highs that may be less than perfect, can sound good to me but then all the fancy test equipment tell a different story and tell me I can't like it. Hmmmmm... Bottom line always is, "but, how does it sound?"
ElPaso TubeAmps I can't break myself of the habit of testing THD at 1KHz, but all my (extensive) musical experience tells me that we should test it at around 200-250Hz, which is where the average male speaks, and where the meat of the sound is for horns, clarinets, bassoons, guitars, ... And you will really hear 2HD and 3HD of a 200Hz tone. I'm also coming round to the the view that PSRR is if anything more important than THD. Look at the IMD caused by the 100Hz ripple around your 1KHz test tone on your spectrum display. The sound of that really cannot be good.
I agree. For really high voltage, I "goop" the capacitors to an insulating board and let them dry overnight. I have experienced arcing from the bottom of some of these capacitors "gooped" directly to the chassis without additional insulation between them and the chassis.
I agree but I did not know that was the asking price for these plug in rectifiers. I have had some of my parts for decades but I do see that prices seem to continue to be going up and up on Ebay. That is outrageous for a couple of diodes. Here is an Ebay listing that I think is reasonable for $12. www.ebay.com/itm/IN1239-Rectifier-1N1239-FAA-5-Pin-Replacement-R21/371837242191?hash=item56933a0b4f:g:dnAAAOSwt5hYdt7A
There are people buying golden fuses and monster cables,why not asking 50 for a 1 dollar bridge,engineers won't buy it for sure.guitarists buy 25 dollars faux bumblebee caps all the time,a sucker is born every minute.
@@moodyga40 Just sent my TH-cam email address to you. I am interested in seeing what you are building. I have worked the night on an 812A push-pull radio frequency amplifier that I plan on running class-C and plate modulating. I still love my ham radio stuff...
In my opinion, the Williamson design using everything from 6AQ5, 6BQ5, 6V6, 6L6, 6550/KT88, etc is an excellent amplifier design to start with. UTC, Heathkit, and a number of others have designs for the Williamson amplifiers that are easy to find on the Internet plus the "100 Amplifiers.... " books I suggested as reference. Best of luck with your build. Please keep in touch and share your experience.
Do think that possibly the reason distortion is not quite as low as others can be phase problem in the feed back I have seen that many tube amps that have super low distortion use like a .0022 cap or something to that effect I find this capacitor very interesting and also quite challenging to get right I also know if u get it wrong it can cause serve problems like arcing across the pins of the output tubes I know the amp will also work without it but I think the high end is less detailed without it what are your thoughts on phase correction in the feedback loop
@@tjasont1 Jason, I completely agree that the value of the FB capacitor is a challenge to get right and "right" seems to be frequency dependent. The old UTC and original Williamson amplifiers do not use the FB capacitor at all. I have noticed that if the FB resistor gets too low in value (and the NFB starts to approach or exceed about 20 dB) the oscilloscope trace will start oscillating up and down at about 1 HZ increasing in frequency as the resistor becomes lower in value and the amplifier becomes more unstable. A 0.0022 uf capacitor seems pretty large but I can't say what it might do. In a few amplifiers I have used a pot to adjust NFB. It seems the more NFB we provide, generally, the better THD becomes up to the point of instability so, in general, I think a good compromise is about 16 dB NFB. To get to that point, I have raised the output to a level where THD is still only a couple %, (with no NFB) noted the power level, did the math for 16 dB NFB and then set NFB for that calculated output power level and let it be. Seems to be a sane way to arrive at a good compromise. I have also noticed that many of the supposed super-high-end transformers actually do not perform very well below 30 Hz or above 15 KHz. At the 20 watt level, the Acrosound transformers are pretty much the King from my experience. UTC transformers seem to have a better high-end than the Acrosound but a poorer low end. Just my experience and opinion.
Thanks, John. I have tried to convince myself to go SET and enjoy 5 watts of musical bliss but I just can't do it. Need that sizzling HV and power to listen to Heavy Metal...
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I heard from Kurt Lillenthal the other day. He was so greatfull for your kind words. You have a fan in him now.
@Hugo Carmelo yup, I've been using instaflixxer for since november myself :)
Hello David, glad to see a new video from you. Really enjoyed you discussing your thoughts on circuit designs while having the schematics in hand. I am absolutely going to download the 4 volumes of 100 amplifiers by Lilienthal Engineering. They look beautiful thank you for mentioning them, I had no idea about them, or that they were available for free. Your redesigned KT88 amp is stunning, truly, you do such neat work, it's something I'm going to try to emulate, and the performance speaks for itself. I just wanted to mention that I make solid state rectifiers using the bases of worn out or broken octal sockets and a pair of 1N5408 diodes (like the 1N4007 but rated at 3 amps) costs about 7 bucks for 50 diodes, so it's really only the time it takes to solder them in place..all of 5 min. Looking forward to a video on that 1948 push-pull James Millen amplifier, another great looking unit and a great piece of history. Hope all is well with you, and as always, work safe.. Take care, Tom
i just built a kt88 williamson. I usually copy the w5m schematic and make some changes to get the right voltages. But it's funny to see that you do it the same way. I also leave out the stabalizing things if i don't need them. I did go back to 12au7s in the preamp part though. great vid! thanks!
Honestly, the 12AU7s are probably a better way to go and that is what I used to use but the 6SN7s with that octal socket are easier to wire. No doubt I have many more good 12AU7s than 6SN7s but I seem to stick with the latter. Thanks for your comments.
Nice messuring Elpaso I'm a diy highend audio tubeamp builder. My setup is ecc83 first tube, fase inverter the 6sn7 and power amped by 6550. Handmade output transformers on old school winding machines. Designe doesn't need nfb at all. Maybe you want to view my schematic, I'm curious about your ideas about it. Well I'll view some more if I get the time. Again nice shag with good messuring equipment.
I built that Williamson circuit, I just gave the output it's own negative supply. and you can bias all of the output tubes individually. I Also doubled the circuit for stereo, I get about 50W per channel 6l6 pp
The Genelex KT88's are great (use them in my tube amps). Keeping the cathode current down to 70 ma increases tube life (this is an issue). It would be interesting to try KT120's KT160's.
Beautiful craftsmanship I hope to be as talented as you you are a great teacher and value your content
Love it all!!!
Thanks for the "100 Amplifiers" site info. Quite interesting and very informative.
Gwenyth Paltrow makes an adhesive for amplifier power supplies? Who'd have guessed?
Wonder if any of her colonics are good for cleaning out noisy pots?
...Thanks for another good video.
That is good to know. Thanks... I have found that the red glyptal insulating varnish is getting hard to come by. I don't need it often but it does come in handy sometimes.
That looks badass !
Love video as always. Are high powered guitar amp power and output transformers inappropriate for hi fi design? Why?
The power transformers from guitar amplifiers would be great.
The output transformers (OPT) from guitar amplifiers do not have the same frequency range as a really "high-end" OPT and I suppose the most discerning ear (whatever that means) from an audiophile (whatever that means) might hear the difference in fidelity between the two types of OPTs.
There is obviously more to an amplifier than the output transformer but at the amplifier's highest rated power limit, it will make a significant difference in total distortion between a high quality reproduction amplifier (i.e. HiFi or stereo amplifier) than a musical creation amplifier. i.e. guitar amplifier. We want distortion, overdrive, crunch, etc in the musical creation amplifier (the guitar amp) but we want the HiFi amp to playback what was created in a "perfect" manner.
With that said, all vacuum tube amplifiers have more artifacts that are created by the amplifier, which we think we are supposed to not have.
I have believed for a long time that we somehow enjoy these artifacts created in the playback amplifiers which adds to the musical enjoyment. Otherwise, why would we still be so stricken and enamored with vacuum tube amplifiers when even a cheap solid state amplifier is likely to outperform virtually any tube amp in lab tests?
Why did you install Chinese film capacitors? Install vima MKP-10.
How many watts will a 83 mercury tube push with a large choke
From the data sheet it can be seen that the DC voltage maximum is around 500 volts and the current is 250 mA. That is 125 watts so it should easily power a 50-60 watt amplifier considering that amplifiers should be seen as about 50% efficient. These are good safe ways of thinking about issues like this. Of course you could push it a bit harder and likely be OK. That is actually pretty tough for a tube that size but what makes it possible is the voltage drop across the tube is low (something like 15 volts for MV rectifiers) so the tube does not run terribly hot.
I think those are 1623 tubes in that amp. And if you need one I have a Raytheon rk-11. It is the same tube. I also have an RCA 811 both are really good if you could use them.
Thank you very much for your offer of the 811s.
I remembered right after the video that the tubes are 812 tubes and not 811. Had one of those "senior moments" making the video.
I have the two in the video and two spares. I really do want to get going on that amplifier and get it on the air.
I thought you got a date wrong in the title at first. You need to look in an amp that I'm working on right now. The McIntosh 50w-2. One of Mcs earliest. Very unconventional. Separate amp and power supply. The chassis's are actually the transformers. They probably weigh 40 lbs a piece. They have two 5U4s. 12ax7, 2-6j5s driving 6L6s. Driver coupling transformer. They are linear from like 5hz to 100khz . I feel privileged just working on them. Can't wait to test and hear them.
Yes, 2020 seems like "back to the future" to me... Wow... I would love to deal with one of the old McIntosh 50W amplifiers. I have seen a lot of them in pictures but never in the flesh. I think Paul Klipsch said, what the world needs is a Good 5 watt amplifier and Frank McIntosh said, what the world needs is a Good 50 watt amplifier. Looks like they both were very successful.
Always informative and interesting to watch. Thanks for another vid!
The plate resistor in a quad configuration allows for current sharing across the paralleled tubes. Look at any high power solid state amplifier or high current linear regulated power supply. The multiple power transistors always have like 0.22 ohm or similar value emitter resistors. Same reason, current sharing. Now I have noticed many OEM quad tube designs of the 60s didn't do this. They just put the plates in parallel. I guess the tube quality of that era ensured highly matched sets. You won't see level of consistency that with today's modern tubes from China and Russia.
Andy, good point about the resistors. I remember the fractional ohm resistors very well in the SS amps. I just figure each active device needs a little "space" of its own, so to speak. It definitely seemed to work well in the UTC W-20 amplifier and it made a whale of a difference in the quad 1625 modulator I built. I am actually convinced from my own experience, if we buy top-shelf vacuum tubes of today, primarily the ones made in Russia, I think they are as good as the USA tubes of yesteryear. I know that some are re-branded, same as always, and the premium tubes of today seem to be nice and strong, well balanced, and they keep their balance. That has been my experience with the re-branded JJ tubes sold by Telefunken and I am thinking particularly of the KT88's. Thanks for your input. Stay safe.
love your videos David wish i was in the usa the learn more electronic valve stuff
Yes! A new upload! Was starting to worry about ya!
I have too many hobbies - fortunately... :-)
@@ElPasoTubeAmps Did I hear you say 'astronomy?'... Please tell us more...
@@thomjmoore Indeed... I love astronomy. I recently purchased a Sony 200-600mm lens that I was out imaging the moon tonight. Just below freezing here so the humidity was down. Pretty amazing what we can do with a camera lens nowadays. I also have recently purchased the iOptron Star Tracker that works quite well and I hope to image some galaxies soon. I have a Meade 10" that I have used and made a number of nice photos with for the last few years. The camera lens won't do what a 10" scope will do but it sure is a lot easier to carry around. Here is one of my first attempts of moon videos that are unlisted on TH-cam. I now use a Sony mirrorless A7RIII camera that I am very pleased with.
th-cam.com/video/P1255sjX9B8/w-d-xo.html
@@ElPasoTubeAmps That's impressive, I have an older Meade 8"..it's good, but doesn't get anywhere's near as clear as that 10". Did you use the A7RIII camera for that?
@@bucyruserie1211 Yes. the 40 Megapixels are amazing. I can blow it up the still pictures to the absolute max and no pixelation. I think you could do some very nice astrophotography with an 8" scope. A critical factor for a SCT is, the collimation must be pretty much perfect but don't turn any one screw on the front of your scope more than 1/2 turn each way. I turned one of mine too far and it came out of the threads and each screw has a spring behind it holding the secondary mirror. I had to remove the corrector plate and get it back together again. I learned the hard way. Now I have numbers on each screw with a dot of finger nail polish on the screw and the scope so I know exactly how much I am turning each screw when I make adjustments and how to get it back to a point where it was perfectly collimated at some point in time and for the conditions for that time. If the collimation is not perfect you get a big tail on stars called coma. When it is set up perfectly, your stars will be as sharp as NASA's.
[sic] Coma is a spherical aberration from rays that come in off-axis. Coma shows up as little off-axis comet-shaped blobs that point inwards towards the center of the field and get bigger as you look towards the edge of the field of view.
Thanks for another very informative video. The 1.5H 500ma choke you use, is that the 159V Hammond from Mouser? Would this choke be a good one to replace the original in a Dynaco ST-70? 73 de KI6DGU
If I remember correctly, it is the 159V but I think it is too large to fit under the chassis of the ST-70. There is one a bit smaller (1H @ 300 mA) that is the 158T that might be a better physical fit. Don't take my word for it without careful measurement of the dimensions on your own. I bought two of each of these chokes from Mouser but have not used the 300mA chokes yet. 73 WA4QGA
@@ElPasoTubeAmps thanks for reminding me about the size; the original C-354 is a tiny thing. Even the 158T is too big, so the 158SA has the correct form factor. Dynakit sells a replacement which is shielded and is rated at 1.75 H and 200ma. The 158SA is 1.0H and 240ma. The original runs pretty warm, so I wonder if it might be better to have the higher current rating and lower inductance (fewer turns) of the 158SA for better reliability.
@@RandyHouk I agree with you. I would go with the higher current rating.
200 mA for the choke is absolute minimum rating as that is the idle current for a quad of EL34 so I consider that a bit under rated.
@@ElPasoTubeAmps I bought and installed a 158SA. It's resistance is 22 ohms lower than the stock C-354, so at 200mA it dissipates about 0.9 watt less. Runs MUCH cooler. I should also add that I replaced the 5AR4 with 1N4007 diodes and a 50 ohm 10W resistor to approximate the tube drop. I'm getting the same 415V at the plates of the 6CA7 outputs. The ST-70 sounds just fine! 73
I have found some transformers that claim to be less than 1 db flat within 10hz to 25khz at rated output at less than 1 percent distortion at 60watts they weigh about 15 pounds a piece the circuit also uses phase correction I do u understand that if the feedback phase is not basically out of phase with the output and becomes in phase it can result in positive feedback and causes all kinds of problems but perhaps the closer u get it to 180 out the more effective it can be and as it moves closer to in phase the less effective it becomes even if it doesn't cause problems just find it quite interesting and wanted to know what u think of this
I have seen those transformer advertisements also and I don't seem to be able to make all of them do what is claimed of them. Many of my amplifiers are built just to test such components as the OPT. Crazy, huh, that I go to that much trouble to test a transformer and see if it does what is advertised? As for phase shift, I am sure you are right about being frequency dependent and as the phase changes from + to - as it passes some frequency, no doubt it factors in to THD values. I have found it pretty amazing that I can get sufficient drive from the Williamson 6SN7 circuit to drive the KT88's to the level of 80 watts at a very respectful THD level. I find that pretty exceptional. I personally like the Williamson 6SN7 circuit. I have built it so many times and whatever comes out of the OPT into the 8 ohm load is usually dependent on the final stage and the OPT and not the driver stage. That may just be conjecture on my part but it is why I generally stick to the Williamson driver circuit.
@@raymondbeard8159 I agree these agree stated response is one thing but these are vintage early sixties transformers I will update on performance I think these might surprise I saw a cary amp that did pretty close to that with 6 six El 34 so it is possible but as far as the phase compensation on the feed back resistor this applies to Williamson designs as well in fact most of all them or infact any design that uses negative feedback I to agree and think maybe Williamson's design maybe tweaked slightly is the best design period
I use goop all the time also.
We don't get to hear the amp?
Hi. What are those test jacks that you like to use?
The red test jacks are connected to the cathodes of the output tubes (KT88's) so I can monitor the voltage across a one ohm resistor and adjust the cathode currents. There is a control at the top rear for bias level and then next to the left KT88 is a balance adjustment. I plug my positive voltmeter lead into the red jack and the ground into the silver (grounded) jack in the middle for each adjustment. You see them from the bottom starting at about 20:00
@@ElPasoTubeAmps Hi, sorry, what I meant was what type are they and where do you get them? Thx, btw. I enjoy your videos very much and I learn quite a lot as well.
@@rickmb6961 Here is one set on Ebay. They come in all colors.
www.ebay.com/itm/4-Pcs-Blue-Insulated-Panel-Mount-Test-Lead-Pin-Jacks-Test-Points-w-Hardware/223716949507?hash=item341691be03:g:m1MAAOSw9w1bqEp4
Hey just a quick question. Maybe someone has asked this before but woulnt it be easier and more accurate to measure both cathodes at the same time and you balance the tubes with a null detector? Then you can adjust the balance easily without having to switch back and forth.
Yes, you can do that. You won't know the value of the cathode current but you can put one lead of your meter on one cathode and the other lead of your meter on the other cathode and adjust the balance for zero. That will work.
Or you could adjust for symmetrical clipping?
@@EJP286CRSKW I think as long as the clipping is mild and just starting, that would work.
can I replace this with 2 of 6L6GC? Thank you
6L6GC can not do what KT88/6550 can.
@@ElPasoTubeAmps That is mean 6L6GC sound worse than KT88 right? Thank you Mr. Elpaso.
@@nuttyl283 No, not at all, the 6L6GC is a good sounding tube but can not deliver the power a KT88 can deliver. I listen to a stereo SET amplifier with 300B which deliver at most about 7 watts per channel and they sound wonderful and are plenty loud. All of the power tubes from the 6AQ5, 6BQ5/EL84, 6V6, 6L6, EL34, KT88/6550 are good sounding tubes. Nowadays there is the KT90 and KT120 which I have never heard the KT120 but I have built amplifiers with the KT90 and they are very good and provide lots of power. Got to remember that assuming starting with a 7 watt amplifier, it takes 70 watts to get twice as loud and then 700 watts to get twice as loud again. It gets pretty insane at that power level. From a 7 watt amplifier to a 100 watt amplifier, that is 11.55 dB. Decibels (dB) is the exponent ten (10) is raised to so, dB is not a very intuitive way of thinking of power and volume but it does allow us to express large changes in power easily. dB levels are always in reference to another level, usually power but it can also be voltage and current, and neither level can ever be zero. We call a level zero (0) dB as a reference level but it can never be zero power or voltage or current. The reason being is in the mathematical formula if you end up with zero in the numerator, the answer is always zero.... if a zero ends up in the denominator, the equation is in error, we can never have zero in the denominator or our calculator will return "error". Hope this makes sense and helps.
@@ElPasoTubeAmps Thank you very much my beloved teacher Mr. Elpaso. Actually I bought many tubes for resell but have very few knowledge about it. My Tube shops who sell me sell 45 2 tubes to me for resell. He said that 2 watts with my 90db speaker is enough 63-73db listening 2.3 meters away in small room. He also sell me many tubes due to he plan to closed shop. I have bought many tube such as 45 6SN7 6P15 E88CC 6L6GC. After I made 4P1SPP due to the cheapest tubes in my stock. I plant to build single end between 6L6GC and 45 to utilize a lot of 6SN7 I have. That is why I ask you schematic of 6SN7 drive 45 or 6L6GC in Single end. I am not sure which one is more suitable to my B&W 603S3 90db. I listen only 63-73db in small room. ttradio.net/the-push-pull-amp/ this is 6L6GC SE or ibb.co/3Sv4268 6SN7 45
@@nuttyl283 I can see you don't need a lot of power but with speakers of 90 dB SPL - that is at one watt, then 10 watts will give you 100 dB SPL, which isn't awful loud and you may appreciate the ability for it to reproduce low frequencies which require the most amount of power. You decide what is best for you but in my case, for my "back house" as I call it, I run my 300B SET amplifier, capable of around 7 watts per channel and my speakers are Tekton which they rate at 96 dB and life is good... and plenty loud. Too loud for my cats...
Here is a link to those speakers and mine are even blue like the picture. tektondesign.com/product/full-range-speakers/full-towers/the-perfect-set/#color
I looked at your two schematics linked in your email and certainly the SET is much simpler and may sound amazing - I have been building audio amplifiers for close to 60 years and until I recently built the SET 300B, there was no way anyone could tell me that it would sound so amazing. The low power SET amplifiers will certainly not perform on the test bench like a nicely designed and built push-pull amplifier and, I can't describe it but they sure "sound" good. I have measured amplifiers that are so perfect in performance but just sound dull. It's true. I have had McIntosh amplifiers for almost those 60 years I mentioned above and they are marvelous amplifiers in their performance and build quality and many can produce huge amounts of power that is very clean and easy to listen to. I have solid state and vacuum tube McIntosh amplifiers and love them for the reasons stated but again, at a loss of words, I really enjoy the SET. I might mention this - the 2A3 is a popular tube but it needs 2.5 volts for the filament - this is kind of nuts in my opinion. The 2A3 was replaced by the 6B4G and has a 6.3 volt filament and a "modern day" octal socket. Makes a lot more sense to me. Then there is the 300B a wonderful sounding tube. Needs 5 volts for the filament but that is much easier to come by. Just something to think about if you choose to use one of those. I am not familiar with the 45 but I see it also has a 2.5 volt filament... The most important thing in using a triode is for it to have a very low gain (mu) and I see that the 45 is very low so it will probably sound great. Keep at it. You will make it work and be pleased with it.
Also who care about high THD above 15 Khz? I can't hear anything over 14khz........:)
I agree with you since my hearing rolls off sharply above 8KHz but some people tell me they can hear (or sense or feel?) the second harmonic to 20KHz. My grandson (18) and my friend that is also my physical therapist can hear 17KHz and I don't doubt it. A 20HZ to 20KHz response with full power across that spectrum and THD under 0.5% is the goal and most McIntosh amplifiers (and your UTC W-20) do just that but some of my much-less-than-perfect amplifiers sound wonderful to me. Maybe it is kind of like homemade beer...
@ElPaso TubeAmps And of course harmonic distortion of a 14KHz tone starts at 28KHz for the second harmonic, which is totally benign, just a sweetener, and 42KHz for the third harmonic, which is not benign, but we are well into dog territory here.
@@EJP286CRSKW Honestly, some of my "lesser" performing amplifiers have sounded marvelous to me. I must like the artifacts of these amplifiers. However, very low distortion in the LF range is very important. This doesn't mean down-right terrible distortion at any point but something about those crisp highs that may be less than perfect, can sound good to me but then all the fancy test equipment tell a different story and tell me I can't like it. Hmmmmm... Bottom line always is, "but, how does it sound?"
ElPaso TubeAmps I can't break myself of the habit of testing THD at 1KHz, but all my (extensive) musical experience tells me that we should test it at around 200-250Hz, which is where the average male speaks, and where the meat of the sound is for horns, clarinets, bassoons, guitars, ... And you will really hear 2HD and 3HD of a 200Hz tone. I'm also coming round to the the view that PSRR is if anything more important than THD. Look at the IMD caused by the 100Hz ripple around your 1KHz test tone on your spectrum display. The sound of that really cannot be good.
Takes a bit to dry.
I agree. For really high voltage, I "goop" the capacitors to an insulating board and let them dry overnight. I have experienced arcing from the bottom of some of these capacitors "gooped" directly to the chassis without additional insulation between them and the chassis.
Why would someone buy one of those solid state rectifiers in an octal for fifty bucks??? A couple of diodes are 50c?
I agree but I did not know that was the asking price for these plug in rectifiers. I have had some of my parts for decades but I do see that prices seem to continue to be going up and up on Ebay. That is outrageous for a couple of diodes. Here is an Ebay listing that I think is reasonable for $12.
www.ebay.com/itm/IN1239-Rectifier-1N1239-FAA-5-Pin-Replacement-R21/371837242191?hash=item56933a0b4f:g:dnAAAOSwt5hYdt7A
@@ElPasoTubeAmps I guessed you had some old ones lying about. It is easy to make one in a nice octal case too if you want.
There are people buying golden fuses and monster cables,why not asking 50 for a 1 dollar bridge,engineers won't buy it for sure.guitarists buy 25 dollars faux bumblebee caps all the time,a sucker is born every minute.
want more valve amp building videos
Hi Ian,
I do plan on some more audio amplifier videos. It has just gotten so hard for me to work on heavy objects but I am not ready to give up yet.
@@ElPasoTubeAmps fabulous i am building an 807 class A amp now
@@ElPasoTubeAmps i have a circuit drawn up for my 807 amp be good to get your opinion lost your email eletrontube42@gmail.com
@@moodyga40 TheAudioShop@SBCGlobal.Net
@@moodyga40 Just sent my TH-cam email address to you. I am interested in seeing what you are building. I have worked the night on an 812A push-pull radio frequency amplifier that I plan on running class-C and plate modulating. I still love my ham radio stuff...
I’m suffering from tube and transformer envy. I can’t wait until I build my first power tube amp.
In my opinion, the Williamson design using everything from 6AQ5, 6BQ5, 6V6, 6L6, 6550/KT88, etc is an excellent amplifier design to start with. UTC, Heathkit, and a number of others have designs for the Williamson amplifiers that are easy to find on the Internet plus the "100 Amplifiers.... " books I suggested as reference. Best of luck with your build. Please keep in touch and share your experience.
Do think that possibly the reason distortion is not quite as low as others can be phase problem in the feed back I have seen that many tube amps that have super low distortion use like a .0022 cap or something to that effect I find this capacitor very interesting and also quite challenging to get right I also know if u get it wrong it can cause serve problems like arcing across the pins of the output tubes I know the amp will also work without it but I think the high end is less detailed without it what are your thoughts on phase correction in the feedback loop
@@tjasont1 Jason, I completely agree that the value of the FB capacitor is a challenge to get right and "right" seems to be frequency dependent. The old UTC and original Williamson amplifiers do not use the FB capacitor at all. I have noticed that if the FB resistor gets too low in value (and the NFB starts to approach or exceed about 20 dB) the oscilloscope trace will start oscillating up and down at about 1 HZ increasing in frequency as the resistor becomes lower in value and the amplifier becomes more unstable. A 0.0022 uf capacitor seems pretty large but I can't say what it might do. In a few amplifiers I have used a pot to adjust NFB. It seems the more NFB we provide, generally, the better THD becomes up to the point of instability so, in general, I think a good compromise is about 16 dB NFB. To get to that point, I have raised the output to a level where THD is still only a couple %, (with no NFB) noted the power level, did the math for 16 dB NFB and then set NFB for that calculated output power level and let it be. Seems to be a sane way to arrive at a good compromise. I have also noticed that many of the supposed super-high-end transformers actually do not perform very well below 30 Hz or above 15 KHz. At the 20 watt level, the Acrosound transformers are pretty much the King from my experience. UTC transformers seem to have a better high-end than the Acrosound but a poorer low end. Just my experience and opinion.
Thanks, you do it to the max!
Thanks, John. I have tried to convince myself to go SET and enjoy 5 watts of musical bliss but I just can't do it. Need that sizzling HV and power to listen to Heavy Metal...