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Old 8th March 2012, 11:07 PM   #1
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Default GU50 Push-Pull version1

I have built some SE and PSE amps with GU50. Now I am developing PP version. This is very first schematic. What do you think? I test Edcor with 6N23P and 6N6P. I got a good frequency response from 100Hz up and about -3dB at 40Hz.
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Old 8th March 2012, 11:30 PM   #2
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It is SE actually since the bottom driver tube is backward-powered. You loose lots of power on phase-splitting transformer that is 15K:600 Ohm. And to get full advantage from GU-50 tubes in pentode mode you need no less than 600V of B+. I use 850V in my Pyramid amps getting 80W per channel.
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Old 8th March 2012, 11:45 PM   #3
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"since the bottom driver tube is backward-powered"

Looks like a typo in the schematic layout, the bottom driver tube is upside down.
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Old 9th March 2012, 09:04 AM   #4
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It is SE actually since the bottom driver tube is backward-powered.
My mistake - I forgot to flip the tube, I will redraw the schematic.
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Old 10th March 2012, 10:53 AM   #5
es345 is offline es345  Germany
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Originally Posted by Wavebourn View Post
... And to get full advantage from GU-50 tubes in pentode mode you need no less than 600V of B+. I use 850V in my Pyramid amps getting 80W per channel.

I have the same experience. In my Bass Amp with 6 GU50 I have 950V of B+ (Idle), the resulting output power is 320Watts. Schematic is attached for info.
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Old 10th March 2012, 11:43 AM   #6
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Originally Posted by es345 View Post
I have the same experience. In my Bass Amp with 6 GU50 I have 950V of B+ (Idle), the resulting output power is 320Watts. Schematic is attached for info.
Hi,

what's the plate-to-plate impedance of your OPT?

Best regards!
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Old 10th March 2012, 11:49 AM   #7
es345 is offline es345  Germany
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Raa = 2K, a little bit lower than the optimum of 2K7
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Old 11th March 2012, 10:23 AM   #8
es345 is offline es345  Germany
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Just another hint:

Using the GU50 it is very important to have a very well filtered 300V supply for G2. If not, get will get a hum modulation of the output signal via G2 especially at high output level.
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Old 11th March 2012, 11:30 AM   #9
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Raa = 2K, a little bit lower than the optimum of 2K7
Ok, thanks!

2k7 would be according to the Telefunken EL152 datasheet, p. 9, last column.

Best regards!
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Old 11th March 2012, 11:38 AM   #10
es345 is offline es345  Germany
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I have tested with another OT at 2K7, the output power was basically the same.
The OT I have in the amp is a toroid one, the other a standard one.

Best regards

Hans- Georg
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