300B Pure Class A Single Ended Triode (SET) Monoblock Tube Amplifiers – Design, Build and Demo

This video documents the design and construction of a pair of single-ended Class A monoblock audio amplifiers using 300B output tubes, and includes some discussion about the design decisions that were made along the way.

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[alexandrutrutiu]

Great project. Thank you for sharing !

[zarzum]

very sweet amp - great work, sir. I am gearing up to build a 300B classic amp and this is a great resource for me.

[janpedersen]

Ultra informative video, thank you! Wish i was smart enough to design a tube amp.

[Sonic_Ox]

Magnificent. You are an artist as well as an engineer. I wish I possessed your capability. Truly fantastic. Best I've seen. Cheers from a neighbor to your south.

[MikeGalusha]

Very much enjoyed the video, thanks for including the shots of SE Amp Cad, Tube Cad and PSU Designer, I use these as well, great tools. Really like the use of the EL-34 driving the 300B.

[astolatpere]

Holy crap, just whipped those out, did ya? Really impressive. Thanks for sharing.

[mfr]

Great job. Thanks for sharing your design and build process.

[vincecuda]

Absolutely Beautiful, obviously an incredible amount of time and detail went into these amps. I would love to get a copy of the final design and layouts to try and duplicate.

[KwokKaySzeto]

Amazing! I have a pair of DIY 300B amplifiers too.

[ElPasoTubeAmps]

You do beautiful work and I am impressed at the harmonic profile at 1 watt. I expected to see a much higher 2nd order harmonic and a descending profile of all the harmonics much like a triangular wave. I have been building push pull amplifiers for a long time and really like the Williamson design but lately I have decided to do some SE amplifier work. I have a bunch of 300B's and started searching for others that have used this tube and found your video. I really enjoyed your video and am a Klipsch owner also with the Klipschorns and other less efficient speaker systems. I also prefer the 6SN7 to the 6SL7 as I do not need that gain from the Aux level devices of today.
One of the reasons I am writing to you is the way the suppressor grid is connected to the plate of the EL34 and the screen is grounded (at lease for signal). I realize the EL34 is a pentode and has three wire grids and is not the beam-power tube format of the 6L6 family but from my experience grounding the screen usually shuts the tube off. Is your schematic accurate or should the connections of the suppressor grid and screen be reversed? Not doubting the performance of your amplifier but just wondering if that is a drawing error.
At the moment, the amplifier I am building will use a choke for the plate load separated by a capacitor and utilizing the full primary of a good quality push pull transformer as the matching inductor to the speaker. Modeling it in LTSpice seems to turn out OK but we know models are not always the real world.
Anyway, I am very impressed with the quality of your work and the results you showed. I think I will be experimenting with a variable NFB control. I made one poor attempt at a SE amplifier years ago using a 833A and a push pull output transformer and even though the OPT would deliver over 1KW of power in push pull, it saturated at 150 mA which was the quiescent current of the 833A. I am going to do it a little different this time... :-) I experienced poor LF response, as would be expected with a saturated core, but I am confident it will turn out better this time. Any thoughts or comments you have are always welcome. Stay safe...

[sonusancti]

Nice job. Wish I had your expertise. My only question is, I noticed the speaker terminals were far away from the output transformers, wouldn't it be better if it were right beside it?

[locmanw]

How much per pair? If possible would like to buy a pair if not too expensive!

[joshua]

Thank you, very informative.
Shame about that couch :)

[bobbysparky]

Excellent! May I ask what the first demo piece you played was?

[woodowoodo]

I see from your circuit you are using AC for your 300b filaments. is that the centre tap connected to ground via a 1k resistor? Do you have any noticeable hum? i have 300bs fed from a 6v transformer into bridge rectifier then into a lt1085 regulator circuit adjustable via a trim pot. It’s reasonably quiet but not silent as it should be. After a few minutes it’s somewhat silent. I’ve never tried AC on the filaments though. btw, looks and sounds great. love the cymbals splashing and the sound of the snare even with the limitations of YT.

[JessHull]

This is beautiful work. This AA34 is beautiful! Do you plan on ever selling any of these? I've always wanted a pair of Tube monoblocks, but have never had the 2 or 3 grand they usually cost.

[jean-yvesvacarme]

Dommage que c'est pas en Français.
Sinon top!

[johnsmith]

Absurd location for the speakers, too close, one playing into a sofa ....

[leeg]

Definitely musical…but not hearing any bottom end bass or punch really, hmmm. IDK.

[Detailverliebt]

Very nice project - if you were Japanese and the monos were green you could sell them for 20 grand (Shindo lab) ;-)

May I ask a question? Please don't take it in any way offensive it is really something I would like to understand. Why tubes? I understand the SE aspect, I understand that nobody needs 50 watts, that's all fine, but good tubes are not available anymore. The last good old GEs and Telefunken and what ever you name it were sold in the 80s-90s where ppl already paid like 1200$ for one 300B and like 400 for a 2A3. The new cheap China tube are pretty much crap and after 6 month of use they start to sound really terrible even with driver tubes like ecc82 ecc83 which should last forever. Why have you not thought about building a true SE transistor amp and I am not talking Nelson Pass style but with a real output transformer. If you say "coz I want tubes" that's fair enough but if there is a technical reason I would be more than interested.
And please don't take it in any way offensive, I am German and that's just the way we ask questions. I totally love your project.