DIY Audio Projects Forum

GU29 Amplifier
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Author:  Piotr67 [ 03 Jan 2013, 04:43 ]
Post subject:  GU29 Amplifier

Hi everybody!

After a nice Single Ended with Russians 6P3C and 6N2P, I would like to start another tubes project, another amplifier, but this time with the Russians double tetrodes GU29, that I have a NOS pair. I like very much the shapes of this tetrode :)
I want to know if somebody has made this kind of amplifier and I want to try a good and tested schematic, whatever if it is Single Ended or Push Pull, but simplest as possible, with schematic, of course, of power supply. I have a few schematics, but I'm not sure how reliable are.

Thanks a lot!

Author:  gofar99 [ 03 Jan 2013, 10:20 ]
Post subject:  Re: GU29 Amplifier

Hi, I have not used the GU29s ,but did use the GU32s in a "oddwatt" circuit. At first I tried to use just one tube per channel in push-pull ultra linear class A mode. The common cathode made it impossible to balance the tubes in the same way as the other amps, so I used the variation similar to the Poddwatts with a CCS in the cathode circuit and variable positive voltages to the grids. idle current was measured across 1 ohm resistors in the anodes. Using roughly 5 volts DC (variable) fed to the grids through a high value resistance on the individual grids I could get them to balance. A second amp I used the 32s in push-pull U/L parallel with two tubes per channel with the individual sections in each tube tied together. Balance was then by the 25 ohm pot I use in nearly all similar amps. In neither amp did I get as much output as I hoped for. I don't recall the values right now, but it seemed to be about 5-6 watts in the one and about 10 in the other. The sound quality of the amps was not up to what I would consider hi-fi standards. Since these are RF tubes, I suspect that the response was non-linear in the power range I desired and was causing a lot of harmonic distortion. Since both amps were significantly below the performance level I felt minimal I discarded the project.

For a general purpose amp they may be suitable. The tubes do look cool though. A pair of EL84s will run circles around them for audio though and you don't need to find the anode clips or funky sockets.

Good listening

Author:  lexx21 [ 03 Jan 2013, 11:07 ]
Post subject:  Re: GU29 Amplifier

Here you go. I forgot where I got this from, but I did buy the tubes to build it but don't have the iron right now. If you use the circuit, let me know how it turns out.

Author:  Soundbrigade [ 03 Jan 2013, 11:32 ]
Post subject:  Re: GU29 Amplifier

Can you share a schematic for the 6P3C? I have some left from my Priboj amp and even though the tube isn't the most reliable tube, it's still awsome to be able to do something with this dual power tetrode.

However, the 829 is said to be very much like a dual 6L6 so you could either start with a schematic for 6L6, with the halves either separately - one half for each channel - or parallelled.
I will finish an 832-SE when we get home from the States. I am using a single 832 (using 6V6 schematics) and, as there's only a single cathode connection for both halves, I have halved the R and doubled the C. As driver a 6SL7, resulting in a two-tube amp.

Author:  Piotr67 [ 04 Jan 2013, 01:13 ]
Post subject:  Re: GU29 Amplifier

Thanks to all for yours early replys.
I still want to make the GU29 amplifier, and I'm waitin' for another schematics and opinions.

Soundbrigade, there is a 6P3C and 6N2P amplifier schematic.
Best wishes!

Author:  RossD [ 04 Jan 2013, 08:28 ]
Post subject:  Re: GU29 Amplifier

What is C5 doing in the above circuit? Feedback or filtering?

Author:  Les [ 04 Jan 2013, 16:58 ]
Post subject:  Re: GU29 Amplifier

g2 bypass? ;)
Seen this arrangement a few times. The one that comes to mind is the Fender Champ 5F1. Drawn a little different, but it's the same arrangement. I was just being silly about a g2 bypass, however, given its value....... Otherwise, it's just a small filter.

Author:  Piotr67 [ 28 Jun 2013, 04:57 ]
Post subject:  Re: GU29 Amplifier

My GU29 PP unfinished amp:

Author:  Piotr67 [ 28 Jul 2013, 23:46 ]
Post subject:  Re: GU29 Amplifier

Testing, testing, 1, 2... :headphones:

Author:  Les [ 29 Jul 2013, 00:01 ]
Post subject:  Re: GU29 Amplifier


I make one little suggestion.... Some clear heat shrink on the anode connections - for safety's sake. Sorry, jus the way I am. I don't like exposed lethal voltage terminals..
Otherwise, very cool looking. Almost "sci-fi"ish -- imagine perspective shooting: tube looks 50' tall with average height humans standing in awe of the tube's glorious power.. :)

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