GU50 Push-Pull version1

[matejsirk]

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]

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]

"since the bottom driver tube is backward-powered"

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

 

[matejsirk]

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]

... 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]

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]

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

 

[es345]

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]

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]

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

 

[Globulator]

Interesting, but the GNFB loop is very long now IMO, 3 tubes, 2 transformers and a capacitor. That's a long journey to correct any errors..

My solution is/should be to limit the feedback to each half of the amp (the push and pull phase split sides), but I'm not sure how good that will be for crossover distortion.

Like the interstage in general BTW, very nice!

 

[Francois G]

Have you continued you work on this amp? Would love to hear about your experience and results.

 

[nerdorama]

I would like to hear about it too. I've got some GU-50's and am planning a project for this winter.
Thanks,
John

 

[matejsirk]

Have you continued you work on this amp? Would love to hear about your experience and results.

That was one of the version. Triode straped GU50 in PP. The front tube was 6350 and the driver 12B4A. The output transformers were 14K:8. I made a mistake when ordering transformers - thats why 14K:8. The power was around 18W. The sound was good. Realy good. Excellent bass.

 

[matejsirk]

And this is my last version, not finished yet. I am still waiting some material.

 

[Ejam]

Matejsirk

Did you ever build this circuit you posted last year? If so, how did it sound?

 

[matejsirk]

Matejsirk

Did you ever build this circuit you posted last year? If so, how did it sound?

No, I did not. It is only simulation in LTSPICE. I have 6 sons and almost no time. Maybe in the future.

 

[Zekk]

The output transformers were 14K:8. I made a mistake when ordering transformers - thats why 14K:8. The power was around 18W. The sound was good. Realy good. Excellent bass.

So, what's the impedance of your OPT?

Thanks!

 

[matejsirk]

primary (Raa) 14K
sec: 8

 

[ui2]

And this is my last version, not finished yet. I am still waiting some material.

I do like your (optical) design very much! Looks really, really cool to me.
Congratulations!
Ulrich