• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

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SE pentode amp

KT66 power tubes, 6SN7 or 6SL7 driver. With different drivers have different sensitivities and different sound.
 

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At first I just wanted to see if I could get any amount of sound out of this set-up. The circuit is a simple 12au7 up front, one triode as first audio, and then the second as a phase inversion driving a 12au7 push pull. The OPT that I used has 34k p to p and 8 ohm on the secondary. All PS caps were bypassed by 1mfd pp. The PS employed was a junkbox PT 136v and then I made a voltage doubler to step things up.
Like I mentioned in the title it was built as a joke, but turned out well for it's power capability. Here it is on the bread-board... I am not sure if I will be building this in stereo yet, as there are better things to do. I did not build from a schematic, so if you would like to try this, give me a little time to draw one up.

Also I have a audio sample for you, the link is to my youtube...
12au7 pp sample amplifier Mono - YouTube
You're not the first to try this. I have seen full-blown ccts.of 12AX7 PP power amps. "Power" - now that's funny. But my 6EM7 SE integrated amp only delivers 1.6W but has no trouble driving my 45kg 3-way 91db efficient towers to a loud volume level with no audible distortion.
 
I have seen full-blown ccts.of 12AX7 PP power amps. "Power" - now that's funny.
Yes, I did try this also, and sounded quite good, but needed a little tweaking at full volume, as distortion was higher with the same OPT. It is a fun tho... And that is why we are here. It is fun to post things, even if it is a breadboard test... I remember years ago, odd test circuits were what got me involved and it has been fun ever since.
Known amplifier designs sometimes become "to easy so to speak" and the unknown tubes become interesting, because a sleeper can be found among the "junk"... LOL
Have a great day