• 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.

GU29 PP Amplifier

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Hi guys , a friend gave me some GU29 tubes , so i want to make a stereo amp with them.
I've a pair output transformers from "Geloso" amplifiers , designed for EL34 in Push Pull , can I use them for gu29 in push pull ? B+ at 400Vdc

What is the ideal Raa for GU29? 5k ?

Can you suggest a good sounding tested schematic? Audioromy ?

This method can be very techy to set up in the first place - not for the faint hearted. I made a small adjustment to the output screens last night and got red plates on one of the PL84's.


i understand, if i were to do this, i will put a 1 ohm resistor at the cathode and 10 ohm resistors at each plate, so that i am able to monitor total tube current and balance plate currents..
"Finished" was perhaps too strong a word. It's electronically done, but I am currently drilling holes in the panel. I used Pete Millettt's mono PP driver boards, so he takes the credit for most of the design.

The last pic I took of it is posted in his pcb thread. Maybe I can link to that pic...

Well, I can link to either the thumbnail or the large image.. If you want to see the larger version, it's here:
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Few questions , screens need a regulated voltage around 200V because of the absolute maximum rating stated in the datasheet right?
My supply would give around 400-450V , really I need a B+ of 600V ? Is just power output related or will work bad at 450V ? Never experienced with this kind of tubes :(

Anyway how much power do I get with theese tubes ?
Screens, yes, pay attention to the max voltage on the datasheet. They don't NEED to be regulated, but a lot of people think it's a good thing to do. If you don't regulate them, give them plenty of headroom for fluctuations in mains voltage.
Plenty of ppl build them w/ the lower voltage supplies. You'd be more in class A. Less total power, maybe less distortion. I'm getting well in to class B territory w/ my loadline.
Power, I'm not sure. At that voltage, look at what people w/ the AudioRomy are getting. (I'm guessing 25ish watts, so maybe 50ish watts if you're going parallel push pull)
I should be getting 80 or more watts out of mine (but have not tested it).

Edit, I should add, If you do regulate the screens, you've gotta regulate the bias supply too.
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