300B SET Single Ended Triode Para Feed 7 Watt/Channel Stereo Amplifier
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- เผยแพร่เมื่อ 22 ส.ค. 2020
- Definitely one of the best sounding amplifier I have ever built or heard music played thru. It does not have the stellar THD performance of a high-end push-pull amplifier but there is just something very clear and alive in the sound of this amplifier. It is just alive much more so than amplifiers that test out better on the bench.
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Beautiful amplifier. Appreciate you taking the time to take us through it. Looks amazing. 🎶😊
I really appreciate all the research and testing that you do. Using all the VRs to bias the drivers. That's great.
Wonderful design. That is awesome. Its good when you talk around the design and explain why's and why-nots, because each little nugget of info helps us all learn that little bit more each time.
Good to see this project finished. Awesome job as usual.
as always very nice work david! great job!
Just liked to say thank for the videos, it's taught me a lot about tube amps, I don't normally work on tubes but am in the process of restoring a leak stereo 20 amp for a friend, uses two el 84 in the outputs & when I get a new toroidal mains transformer will be working fine againbest wishes Nick
Thank you for mentioning the NFB and Cathode bypass capacitor on the same gain stage. I think you just solved a problem on a few of my builds. ; )
I would consider buying this
I was just thinking that you have not posted a video in a while, and here it is!! Love the amp, I don't know why.. But I just think they are great. Yeah I don't know who made the comment about the negative feedback, but you have shown the benefits of global feedback many many times.. Be well, Tom
Nice work as always, especially like the idea of using a PP OPT with DC blocking caps as a SE OPT. Thanks....DA. PS got a spare type CA plugin but shipping from the UK might be too costly.
need to slowly study this clip. very beneficial to newbie as me.
Thanks, David. What have we learned? 1) NFB is your friend 2) back-to-back polarized, high-value electrolytics can be used as coupling caps 3) simple designs might use massive iron 4) 5 watts is enough 5) boat anchors are wonderful to listen to... :-) I always learn something valuable from your videos. Be safe.
The video looks pleasant and sounds good. You put your heart into it, so do I, ha ha
Although I'm not up to the task of engineering an amp from scratch.........I got a DIY kit for a 300B unit. The other tubes were under their international names, but it's a 5u4 rectifier, and 6sn7 driver tubes. I enjoy it very much. It's a different sound, and I've heard new things in recordings that I knew quite well.
I think you stated it nicely - it is a different sound and seems more alive. None, or very low, negative-feed-back (NFB) changes the tone of an amplifier. Years ago I built an amplifier with a NFB adjustment (0 to 16 dB NFB) and when the feedback was turn out or very low, the amplifier seemed to come alive and I labeled that control as, "sound stage". On the other hand, if amplifiers like the SET or any other amplifier with very low or no NFB are measured on the test bench, it will be clearly seen that frequency response is technically terrible, i.e. the mid frequencies are much higher in amplitude than the low and the high frequencies which is the opposite of the classic Munson Fletcher curves - but then, maybe that is why we tend to like it. Bottom line is always, how does it sound? I find the SET amplifiers to sound good on some classical music but they quickly run out-of-steam on heavy metal music. 🙂
AWESOME!
It took you a while to realize what a SET can do. I built a 2A3 SE amp that I listen to all the time. Same 6SN7 drivers. I use 5692s in mine. Still thinking about those 6080s. Haven't found a transformer yet to handle the filament current. Will probably end up using a dedicated filament transformer. My 2A3 I'm using AC on the filaments with no problem. Nice ceramic tube sockets you used on those 300Bs.
As I have heard said, and repeated, they are a bit addictive. Very open sounding and alive. And with just my 5 watts per channel and inefficient speakers, it will really impress and the bass is great. I was very concerned about the LF response. Apparently I got enough L in the plate path to do a good job.
Great looking piece of equipment.
Great looking SE Amp. They are definitely different in character and like you, I do find them really pleasant especially as you go up in frequency. Also, you may find that the tube trigger in your Tektronix 535A scope will trigger on things later solid state scopes throw up their hands with. And forget the CA.,.. You want a 1A1 instead.
We agree on several things here. I just spent some time with my friend and the SET on his Tekton Moab's and that little SET amp will leave you breathless. He has a beautiful McIntosh 225 that sounds as good but the SET has something extra special about it. I was concerned about LF response. That was definitely not a problem. Absolutely amazing sounding amplifier and system. I just got some nice inductors from my friend in Poland so I will be starting on another SET using the Svetlana SVT572-10 and see how it turns out. I also agree with you on the trigger of the old vacuum tube Tektronix. It is amazing that the trace still centers with the knobs in their center position. It just works. I will look into the 1A1 preamp. Thank you.
@@ElPasoTubeAmps I have a 1A1 that needs some TLC if you want it. Check out Toriody in Poland if you haven't already - fantastic toroidal iron. My SE project used 3 6EW7s for an output stage into a One Electron UBT-1 1600-4/8/16 output iron and uses a 6GK5 with a 6GK5 plate load on input (current sourced plate-load input/driver stage). The 6GK5s high mu and low Rp made a great input/driver for the tripled up 6EW7s on the output stage, and the low impedance ratio on the output iron means I get about 8 watts at clipping and 26dB of gain without feedback. I have a switch for 3 or 6dB of feedback overall. I am currently using a pair of them on tweeters (upstage active crossover) and a push-pull 7591 with cathode feedback on woofers. w140.com/tekwiki/wiki/1A1
@@jasonagee385 Jason - I would love the 1A1 - I will put it back to work and show it on TH-cam. I assume it "works" but just needs a little TLC? I see the CA preamps on Ebay but most have been robbed of tubes. Oh well... I will be happy to pay the shipping if you want to send it to me. Direct email is; theaudioshop@sbcglobal.net.
As for the SET, I listened to my 300B SET yesterday along with a beautiful McIntosh 225 and both were amazing. I gave my friend with the Mac 225 a set of tubes for it including a quad of actual McIntosh branded 7591's that I remember changing out in a MA230 I bought for my Mother back in 1976. Saved them for 44 years and they are all four very strong. You know how hard it is to find "perfect" quads of vintage tubes nowadays. I also gave him Amperex bugle boy 12AX7 for the first stage, RCA 12AU7 clear-tops and RCA 12BH7's. I was glad to put those beautiful tubes in an amplifier that deserved them.
As for the 300B SET that I built - it is amazing. It is every bit the Mac 225 and maybe I even hear nuances in the SET I don't hear in the Mac. Not sure as we only listened for a couple of hours to five pieces on one amp then the other. Wow, is all I can say for the 5 watt SET. His speakers are the Tekton Moab at 98 dB SPL. I hope to get started as early as tonight on the next SET with Svetlana SVT572-10.
As for the iron, I just got six inductors from my friend in Poland. Here is his TH-cam channel: th-cam.com/video/RFyC1-aPI3w/w-d-xo.html
I'm not much I to hifi amps as there's to much audio foolery involved but I like your work. Excellent videos.
I build guitar amplifiers using all the original parts from a given era, be it 1920s 30s,40s etc. Maybe try your hand at a few instrument amps?
Distortion is king rather than a curse
As it will equalise the voltage across power caps
I want to hear it.
I think this would be a very interesting question. Justin Johnson performs excellently, as he does. But when he performs New Orleans Heavy Swamp Blues on a six string fretless. It is a sight to behold. How do you explain his magic from 3:15 to 4:39? Mysterious, yet excplainable, if you would. :)
Excellent project results. Glad you are going to bring it in and enjoy the audio bounty of this one. What speaker did you order to go with it? Horns?
Bill
I just ordered some Tekton speakers rated at 96 dB SPL, the model is "The Perfect SET". The speakers I use it on now, and it gets plenty loud are only 88 dB SPL and are called Dahlquist DQ-20. I got them a few years ago at an estate sale for little money. I have Klipschorns in the house but I will likely use the SET amplifier in my back-house apartment. The room is 20x20 which probably places speakers a little too far apart for the best stereo experience. The no NFB SET has a certain addictive sound, as others have called it. It does a good job with classical and heavy metal. LF response is not lacking. This amplifier is fairly easy to build without expensive special SE components. You can probably find a little more information on the Internet by looking for para feed SET amplifiers.
The 'flatness' you hear with GNFB is just (a) flat frequency response and (b) controlled gain, as opposed to uncontrolled. Without NFB the gain is a function of the actual tubes, actual line voltages, HT voltage sag, and temperature: some of which in turn is a function of immediate past program level. So what you hear is signal-modulated gain. In other words, compansion.
Wow, EJP. thanks so much for this superb explanation - "signal-modulated gain" - does this not get us into radio frequency broadcast land?
Just as I thought I had discover audio Nirvana in the humble SET - the true beauty of audio clarity with no GNFB, sold to me when I was young by (scoundrel) audiophile expert salesmen (and women...) you remind me that GNFB Matters (pun intended?)... you know I am kidding with you.
Yesss..... NFB is my friend but that accentuated frequency response and uncontrolled gain of sag and rise, just reminded me of my girl friend back in 1967... but I have to be a grownup and not be modulated by my feelings... no compassion or expansion, just compansion.. :-)
Radio Jet Thanks. I came to this conclusion while listening to my first SET, in for a service, 300B thing, about 700V on the plates, so terrifying I had to power it up outside the first time. I noticed immediately that I had to keep turning it down, whereas with the normal run of equipment being tested I can set the level once and maybe tweak it once and that's it. So I sat there thinking 'this is getting louder ... but that's impossible ... gain is set by the ratio of two resistors ... err, no it's not!' And then thinking through the implications. Sure it sounded lively, and the succeeding NFB amplifier did indeed sound 'flat' ... But that's why.
@@EJP286CRSKW You know I understand and greatly appreciate what you wrote. You are right. I just had to try the darn things and experience them firsthand and had the parts and the fact that it just seems to keep getting louder is the same thing I have experienced. A properly operating Williamson design is hard to beat.
Oh well... not sure what my next project will be. I have two magnificent UTC LS-35 that are 5K primary that I want to use with Svetlana 572-10 (the 10 means mu of 10) triodes in monoblocs. I have everything from all the transformers to the chassis and sockets, etc. Just got to get around to doing it. I hope you are doing well and staying safe.
@@ElPasoTubeAmps They told you way back when you were young and naive that life would be linear and there would be no "accentuated frequency response and uncontrolled gain of sag and rise".That's only because they had no idea how much fun life can be when it catches you off-guard with a bit of all that. The Universe is not a Clockwork Orange, IMHO. It's more like a good Jewish or Italian deli....with discounts for old audiophiles and the like....... thanks for your excellence.
@ElPaso TubeAmps I'd like to build this or similar. I suppose a BOM is not feasible with mil surlus xformers, but a schematic with voltages would be great. I for one would be interested in a SPICE model overview with starting tips for modeling noobs,
I show a schematic around 11:20. Maybe moving the camera around too much to be easy to see. I probably have a LTSpice schematic of it if that will help you but no BOM except in my head.
Beautiful amp! Non-technical question; admiring the quality of your tube labels, they almost look silk screened. What brand Labeler do you use?
It is actually just clear labeling tape. I agree, it looks much better than the black-on-white background. I use it in a Brother P-touch. It is type, TZ-131, CLEAR
Excuse me can you show schematic of B+ 416VDC Mr. Elpaso
You should give a 45 SET a go. Time for a new build. You know you miss it, it’s in your blood.
I think I have some 45's. Good idea - Thanks 🙂
From Sowter UK I just now understood how important the plate choke is to feeding good sound through the primaries of the OPT, by reducing B+ ripples. BUT MAN is it expensive to have the best quality of chokes.
I just wonder. Do you think it makes one hell of a difference in sound?
My SET amplifier uses chokes as a plate load because I did not want to invest $$$ in SE transformers as I had no confidence that a SE amplifier would be acceptable. The chokes are the DC feed to the anode and the signal load parallel with the James OPT. I already had the chokes and James transformers so I think you can see why I did it this way. I am very pleased with the sound but sometimes want more sound level than 7 watts can provide.
There seems, from what I read, to be characteristic issues with SE amplifiers - one is attenuated high frequencies, probably from the excessive capacitance in the OPT windings and some complaints of hum. Not sure why hum is an issue unless there is a power supply issue. For audio amplifiers, in my opinion, a choke should always be used in the PS along with an input and output electrolytic capacitor to form a Pi network. PS chokes do not need to be large in inductance - better spend money on current level. A way to estimate minimum choke value is to divide the plate voltage by the minimum idling current in mA. Assume 450 volts for the plate and a quiescent plate current of 80 mA - typical of a pair of 6L6/KT66, the choke can be as small as 450/80 = 5.6H. For a stereo amp that would be 450/160 = 2.8H. Hope this helps.
Thanks for your comments.
How does NFB compare to damping factor?
I had a Bogen tube amp with adjustable damping factor pot on the back, but never figured out what it does. It did make a big difference in the sound though.
Nice looking amp! ALL your work is wonderful though!
I am no expert in mechanics but it goes something like this.
I remember from a mechanics course that a car with shock absorbers has two parts in the suspension system - the sprung mass and the un-sprung mass. The sprung mass (the entire body of the car and engine + passengers) and the un-sprung mass is the wheels. The shock absorbers are the damping factor. When a car hits a bump or a pot hole, the un-sprung mass goes into the hole and energy is transferred into the shock absorbers and a correct damping factor of the absorbers causes the body of the car, and its riders, to be, as best as possible, insulated from the impact of the wheels. If the shock absorber is perfect, the car will completely recover from the impact in about 1.5 cycles. i.e. the positive amplitude of the impact will be lessened by the shock absorber and the negative amplitude will be greatly reduced below that of the positive amplitude and within the next cycle the car will be level again.
I hope I said all that right. So, with a speaker, depending on its efficiency, the effective damping of the output circuit of the amplifier and the speaker combination is an equivalent circuit of the car and shock absorbers. If the speaker is inefficient, (say, 88 dB SPL) the damping factor needs to be higher to properly stop the "ringing" and "boomy" sound of bass and if the speakers are highly efficient (say, 100 dB SPL) the damping factor can be lower. In a perfect world, speakers and amplifier should be "matched" for best performance.
Back to the original question - global negative feedback (GNFB) or just generally written NFB, will not only significantly reduce THD, it will increase the damping at the output terminals of the amplifier, giving the amplifier more control of the speaker, i.e. a stiffer shock absorber with NFB. Almost always a good thing.
As for your Bogen amplifier with an adjustable damping factor pot, I suspect it was simply a variable resistor in the NFB path. Increasing the resistance in this path reduces the NFB, lowering the resistance (but not too low...) increases the NFB along with the damping factor. Increased damping factor is a result of NFB. Some of the older Fender guitar amplifiers had an adjustable NFB pot also. Decreasing the NFB greatly increased the gain of the amplifier along with THD but that can be a good thing in the hands of a musician.
SET amplifiers with no NFB are more likely to sound boomy on inefficient speakers.
Years ago, high quality speakers were almost always highly efficient, and expensive because of close tolerance voice coil and magnet assemblies, but somewhere around the 1970's the "acoustic suspension" speakers came out (cheaper to make). These are the ones that are very inefficient and want huge power amplifiers to drive them. Acoustic suspension speakers are the ones with soft outer suspension rings (the ones today that are often times rotted off) that have to be installed into a closed box full of absorbing material (the internal cabinet pressure created by the bass speaker is a form of mechanical NFB). High efficient speakers are built into "ported" cabinets where the reflected bass comes out the front under the cabinet or a hole in the front of the cabinet or is ported to the rear of the cabinet into a corner for better bass response.
I was told "back then" that amplifier power was cheaper than speaker efficiency and that is why these speakers became so prevalent.
I hope this is worth something.
@@ElPasoTubeAmps WOW thanks ALOT for your detailed explanation! Makes alot of sense.
Yes, I am familiar with acoustic suspension speakers, and know that they are very inefficient.
Never really liked them due to their huge power requirements.
yes, the damping pot was just a pot, and I did reverse engineer it when I had it, and it was in the NFB path.
If I remember correctly, if the pot was set at one extreme, the output would try to oscillate when driving lower frequencies... it would never break into oscillation, but was trying to oscillate.
Makes sense now that it was basically a variable feedback.
It was a "fancy" amplifier... had several eq. curves for the phono input... RIAA/EIA/78/flat/and some others.
Thanks for the videos. Question: I have a 2.5 watt monoblock 45's, I have moved and my space is limited so I connected them to my Vandersteen 2ce Signature II's. It sounds amazing, but people have told me I will hurt them amps because of the load. Does that sound accurate, or keep on truckin'?
I wouldn't worry about it for a heart beat. A 2:1 mismatch in speaker/amplifier impedance or any amount of SPL sensitivity, gain or loss, is not going to hurt the amplifier especially at the power levels of these SET amplifiers. At 100 watts or more per channel, we might want to be more careful. Keep on truckin...
ElPaso TubeAmps Thank you much, sir. I appreciate it. I will get back to it.
Where is good spot to buy tubes?
@@RobotronR6 I buy all my new tubes from www.tubedepot.com. They have been very good to work with and they sell pretty much everything else too.
Also, keep in mind www.mouser.com and www.tubesandmore.com. They are also good sellers.
Good point @ElPaso TubeAmps. Should have been obvious from my RF days e.g. toy handie-talkies vs 5 watt vs kilowatt gets more critical. Milliwatts vs tens/hundresd of watts reflected - huge difference.
Hi there! You have some nice interesting video's how about some about guitar amps?
I did some guitar amps a few years back and posted videos on them. I don't work on them anymore as they are too heavy and large for me to deal with. You might like some of my older videos.
You should try good quality switch mode power supply running at 120khz works fantastic with valve amplifiers
Hi John,
A few years ago I bought several SMPS and found they are quite powerful, especially for their size. That is a good idea and maybe an approach for a smaller SET using the line transformers we have all talked about so many times.
Are you keeping all your home brew amps? Must be quite a lot
I am ending up with quite a museum of amplifiers in my basement. I used to take them apart when I wanted to build another but they are accumulating nowadays.
From your experience, how would you compare these tube amp to a SS amp where it costs around $20k +? I don't have tube amp so I am not sure if I want to get into tube or just stay with SS. Thanks
it seems many people prefer the sound of the tube amp to the SS amps. I have several high power McIntosh SS amps and they sound good but the low power SET amplifiers just have a "life" and amazing sound to them. I have recently changed from all of my high-end tube and SS amps to the 5W/Ch 300B SET amplifier. I do want a little more power, maybe 20 watts per channel and is why I am building the Svetlana SVT572-10 amplifier.
@@ElPasoTubeAmps Thank you so much, I will look for 300B to try.
Not sure I understood your setup to supply 5v from a 6.3v winding. I heard 100ohm but that doesn’t add up. I assume you meant 100watts 0.68 ohm or similar?
I put the 100 ohm resistor in series with one leg of the 120 volt input primary side of the transformer so the 6.3 volt secondary would only deliver 5 volts under load to light the filaments of the 300B tubes. I did not have a 5 volt filament transformer so I used a more common 6.3 volt transformer but had to drop the secondary voltage down to 5 volts. Hope this helps.
@@ElPasoTubeAmps ah! Make perfect sense thanks.
nice video but is it possible your website is offline? I tried to check what I saw on the badge you have on the amp but it sends me to one of those "buy this website" pages
I first made that website years ago but let it go as I did not want another email address, for one thing. I also foolishly opened it up to the world and within a few days had something like 65,000 posts from Russia for porno sites. Well, that did not work so I changed it to just redirect everyone to my TH-cam site. Then when I let it go, as it served no real purpose, someone bought the domain and now wants something like $350 for me to get it back. Oh well...
@@ElPasoTubeAmps Don't give in to that and let him waste his money, more fun for you
I think for long term reliability you need to add resistors 470k across series connected capacitors in power section
I agree with you. I probably will do that soon. Thanks for reminding me.
@@miles5681 resistor is not required for one capacitor. And even if you are using two capacitors then use 470 kilo ohm rated at 2 watt and not 470 ohms
Very nice. Sign me up for your amp building class. ;)
What would an amplifier building class look like? Seriously, think about it and break it into maybe five videos. I could talk about it for a month and digress from one of the spectrum to the other but it should be more focused than that. I am interested in your thoughts.
Very generous of you to consider the idea. A rough sketch would be:
1. The finished build with a circuit diagram, parts list and commentary on tools or testing equipment that someone might not consider necessary, some safety tips, and general comments.
2. Order of assemby (macro level). Commentary on what areas will be assembled first and why, i.e. work flow. Starting the build with lots of images so people can compare their work to your work.
3 &4. Assemby (micro level). Images (lots) and commentary on building that include, tips, things you've learned the hard way, necessary mid build testing, etc.
5. Finishing the build, testing, and tweeks.
My thoughts are for a detailed follow along build not a skills class, like how to solder, there are plenty of those on the internet. Thank you so much!
@@chubtoad157 That is a wonderful plan to follow. I really appreciate you taking the time to write it out. I have copied your text into a Word document and plan on using it in a future build. Many thanks...
@@ElPasoTubeAmps Just came across your page and would 2nd you amp building class. Would love to build one of these myself.
Mr. Elpaso please provide video how to draw load line on tube graph. How can we know that what tube need how many K AC OHMS in OPT? Such as 45 need 5K or 7K OPT how to calculate to get 5K or 7K. Thank you for video in advance.
I am really not the one to make a video on how to draw load lines for vacuum tubes. However, I do recommend this video: robrobinette.com/Drawing_Tube_Load_Lines.htm
If you are willing to go thru all the details of this video, I am confident it will help. I did go thru his video and he makes some very good points besides just load line analysis. It is worth taking the time, in my opinion
As for the OPT, I could probably do a reasonable video on that. But in its simplest form - using the 300B as an example - virtually all of our amplifiers are class-A. They may also be run as AB1 and AB2 but they are still essential class-A. In AB1 and AB2, we just drive the grid positive a little bit - this gives us a lot more power with increased distortion. The class the tube is run in is primarily determined by its bias - and the gain of the tube. Low gain (low mu) triodes make great HiFi amplifiers in class-A and great plate modulated class-C amplifiers for RF. It is a long and laborious subject so have fun digging thru the details. Stay safe...
@@ElPasoTubeAmps Oh Thank you so much Mr. Elpaso
Filament balance volume. What is it how value of adjustable resistor and how many pins of it?
The filament balance pot is 50 ohms set very close to center, about 25 ohms on each side, to as close to perfect as possible, reduce any power supply hum to minimum. It is thru this resistor that the current thru the tube goes to ground. There are three pins on it just like any (volume control type) potentiometer. One side goes to one filament pin and the other side goes to the other filament pin and the center pin (the wiper) connects either directly to ground or to the cathode resistor that goes to ground. This cathode resistor may have a capacitor also across the resistor.
Bias can be applied to the tube grid from a separate negative power supply or bias can be obtained by putting a resistor of correct value in the path of the cathode (in this case the center of the filament-balance-pot) to ground. A voltage will be developed across this cathode resistor of some value (around 60 volts in this case) and because of the action of the vacuum tube, this same value voltage will appear from grid to cathode in opposite polarity making the grid negative with respect to the cathode. This is called the bias. A very common error in analyzing a vacuum tube circuit is to think of all voltages " to ground ". Voltage is "across" a component, a resistor or tube elements, i.e. from grid to cathode in this case and current is the actual physical number of electrons flowing thru the tube. There are 6.242 x 10^18 electrons per second flowing thru a point in a circuit for one (1) ampere. That is a huge number but electrons are really small. :-)
In electronics we generally think of current flowing from positive to negative. This is strictly for convenience and ease of analyzing the circuit.
In physics it is looked at as current flowing from negative to positive since negative implies an abundance of electrons flowing to the positive side.
It doesn't matter which way we look at it as long as we maintain the same method throughout the circuit - meaning, you can't analyze a circuit by thinking of current flowing one way in part of the circuit and the other way in other parts of the circuit.
One last thought - in many cathode biased circuits there is a capacitor added across the bias resistor. What this does is allows the DC voltage to be stable thru the resistor but it allows the AC component of the signal, the music or voice, to go straight thru the capacitor bypassing the resistor. The capacitor "bypasses" the cathode resistor for the signal voltage without affecting the DC value of bias voltage. This almost always raises the gain of the circuit. It is often a good thing to increase the gain of the circuit but not necessarily good in all cases.
@@ElPasoTubeAmps Thank you very much Mr. Elpaso. Is it 3 pins? 50Ohms 5 watts?
@@nuttyl283 You can hook it up just the way the schematic shows you or simply replace those two resistors and the 1K pot with the pot you describe above. 3 pins, 50 ohms, 5 watts should work just fine. What you are doing is providing a path to ground for the cathode current and, with the pot, "balancing" the current from each side of the filament to reduce the hum coming out of the amplifier. If you do not have equipment to measure the hum, you can just adjust the pot to where the hum coming out the speaker is at its lowest point.
@@ElPasoTubeAmps Thank you for the reply. This helps so much.
7:40, not enough iron in the output transformer.
Did I miss the operating point of the 300Bs? Also many 300B amps claim higher output. I realize the increase of distortion is so linear that it is a bit arbitrary whatever the power claimed. Just wonder why you are claiming 5 watts?
I am very conservative in claiming power ratings. If i remember correctly, it runs at about 1% THD at something like 6.5 watts? 5 watts is where it performs really nice. I suppose I got that from McIntosh amplifiers. It they say it will do 30 watts it will probably do more than 40 and still perform perfectly. That is true with all their amplifiers.
@@ElPasoTubeAmps so 400v @ 60ma?
@@meshplates I remember that the plate voltage is 416 and it seems the bias was about 63 volts. That would be 77 mA as the cathode resistors are 820 ohms. Next time I have it on the workbench, possibly tonight, I will measure and note it so I can tell you exactly.
My data for posterity:
I recorded data for both channels and they are so close it is not necessary to post data for the right channel as it is essentially the same.
_______________________________________________________________________________
Filament voltage at socket, 5.51 VAC
All voltages below are measured to ground.
Plate voltage, 401 VDC (687 VAC secondary winding of power transformer into FWCT and capacitor input Pi filter)
300B cathode voltage to ground across 820 ohm resistor, 66.8 VDC (bias) (81.5 mA)
plate voltage on first stage of 6SN7, 69.3 VDC
plate voltage on second stage of 6SN7, 210.7
cathode voltage first stage of 6SN7, 0.952 VDC
cathode voltage second stage of 6SN7, 74.1 VDC
Left channel at 5W, 0.244 % THD
Right channel at 5W, 0.297 % THD
Left channel power at 1 % THD 6.32 W
Right channel power at 1% THD 6.35 W
______________________________________________________________________________
@@ElPasoTubeAmps thank you so much. I really appreciate your effort!
Make it commercial and put a real price on it so you can continue making them!
My wife would like that ... someday I think I will start selling my amplifiers, probably here on TH-cam. I will not sell on Ebay anymore. I buy lots of things off Ebay and have had phenomenally good luck with only 2-3 bad experiences in over 10 years. I have also had some wonderful customers on Ebay when I was a seller but I am not a tough enough business man and seller and when I experience a buyer that hacks the price down after the sell when I know there is no real problem, it turns me off and I just don't want to deal with Ebay and PayPal as a seller any more. Ebay is 100% on the side of the buyer - not the seller.
I know that using AC for your filaments/heaters is rarely a problem Re: hum, but I think a big part of it is just people being anal retentive sticklers. Purists. As it turns out, I'm "people." Using a simple solid state (gasp!) rectifier (or a homemade one with four diodes) and an electrolytic capacitor adds so little complexity or expense to the overall design that it seems practical just to sleep well at night. To each his or her own I suppose - I can't claim to be much of a purist because I still see no problem with solid state rectification for even your B+ honestly, and every argument I hear against it sounds less scientific and more like people trying to promote astrology. Anyway, great vid!
Do u consider to sell it.??👍👎