GU50 Push-Pull version1

matejsirk · 8th March 2012, 10:07 PM

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.

Wavebourn · 8th March 2012, 10:30 PM

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.

smoking-amp · 8th March 2012, 10:45 PM

"since the bottom driver tube is backward-powered"

Looks like a typo in the schematic layout, the bottom driver tube is upside down.

matejsirk · 9th March 2012, 08:04 AM

Quote:

Originally Posted by Wavebourn

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.

es345 · 10th March 2012, 09:53 AM

Quote:

Originally Posted by Wavebourn

... 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.

Kay Pirinha · 10th March 2012, 10:43 AM

Quote:

Originally Posted by es345

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!

es345 · 10th March 2012, 10:49 AM

Raa = 2K, a little bit lower than the optimum of 2K7

es345 · 11th March 2012, 09:23 AM

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.

Kay Pirinha · 11th March 2012, 10:30 AM

Quote:

Originally Posted by es345

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!

es345 · 11th March 2012, 10:38 AM

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

8th March 2012, 10:30 PM	#2
Wavebourn diyAudio Member Join Date: Sep 2006 Location: Pleasant Hill, CA	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. __________________ If I disappear suddenly, that means I finally created a time machine and pushed wrong button that brought me to Stalin's Russia. In any experiment any result is the result. Even if it is negative.

8th March 2012, 10:45 PM	#3
smoking-amp diyAudio Member Join Date: Dec 2001 Location: Hickory, NC	"since the bottom driver tube is backward-powered" Looks like a typo in the schematic layout, the bottom driver tube is upside down. __________________ Ohms Law V = I R

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10th March 2012, 10:49 AM	#7
es345 diyAudio Member Join Date: Jan 2012 Location: Ulm	Raa = 2K, a little bit lower than the optimum of 2K7

11th March 2012, 09:23 AM	#8
es345 diyAudio Member Join Date: Jan 2012 Location: Ulm	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.

11th March 2012, 10:38 AM	#10
es345 diyAudio Member Join Date: Jan 2012 Location: Ulm	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