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Old 27th February 2013, 09:00 AM   #1
Tesla88 is offline Tesla88  Italy
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Default GU29 PP Amplifier

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 ?

Thanks
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Old 27th February 2013, 10:03 AM   #2
SVStube is offline SVStube  Ukraine
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http://lynxaudio.narod.ru/articles/Lynx_VTA39.pdf
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Old 27th February 2013, 10:09 AM   #3
AJT is offline AJT  Philippines
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nice sounding tube, i had a chance to repair an Audioromy....it can still be optimized...

5k push-pull will work, the problem with this tube is idle current bias matching on the plates, this you have to watch out for....o got red plate on one side of a new tube....
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Old 27th February 2013, 10:18 AM   #4
AJT is offline AJT  Philippines
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Originally Posted by SVStube View Post
thanks for the link, if i were to build this amp, i would put 10 ohm resistor in series with each plate so i can check plate current balance....
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Old 27th February 2013, 10:35 AM   #5
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Raa depends on Ua and Ia.....
Hope you have a big stash to find a few with matching systems (especially in gm, static match can be adjusted via bias voltage)
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Old 27th February 2013, 04:45 PM   #6
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Can I suggest you look at my DC7 Mk3 thread to see a way of biasing up a shared cathode output tube. Its self adjusting and stable if the input valve stays reasonably well matched.

Shoog
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Old 27th February 2013, 09:43 PM   #7
AJT is offline AJT  Philippines
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Originally Posted by Shoog View Post
Can I suggest you look at my DC7 Mk3 thread to see a way of biasing up a shared cathode output tube. Its self adjusting and stable if the input valve stays reasonably well matched.

Shoog
links please...
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Old 27th February 2013, 10:19 PM   #8
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DC7 MK3 up and running.
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Old 27th February 2013, 10:22 PM   #9
AJT is offline AJT  Philippines
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thanks...
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Old 28th February 2013, 03:28 PM   #10
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Originally Posted by Tony View Post
thanks...
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.

Shoog
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