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Pentode curves for GU 50 SE amp with 700V B+

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hi I have breadboarded a GU 50 SE amp in pentode mode.B+ is 700V G2 is 250 Volt and my transformers Ra is 2,5k.I know that Ra is a bit low for that but the transformer is a left over from some other project. At the moment I use a 470 ohm resistor with 220uF for cathode bias,but I want to calculate the right resistor.Unfortunately i can only find triode curves but i need them for pentode mode.
 
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hi I have breadboarded a GU 50 SE amp in pentode mode.B+ is 700V G2 is 250 Volt and my transformers Ra is 2,5k.I know that Ra is a bit low for that but the transformer is a left over from some other project. At the moment I use a 470 ohm resistor with 220uF for cathode bias,but I want to calculate the right resistor.Unfortunately i can only find triode curves but i need them for pentode mode.

http://www.mif.pg.gda.pl/homepages/frank/sheets/018/g/GU50.pdf
 
Ub=700V is used for PP class AB, you will not get satisfying result for SE operating mode.
If you want to use pentode mode: Just as a top down estimation you should go to B+ of about 400V, GU50 operated at about 80-100mA . Then you could use your OT with 2K5. Looking to the datasheet you need a bias of about 25V. I would start with Rk of 270 Ohm.

Have a look here http://www.diyaudio.com/forums/tubes-valves/196811-help-these-russian-gu50-tube-amplifier.html (GU 50 SE in Triode mode, this might be a better solution)
 
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Ub=700V is used for PP class AB, will will not get satisfying result for SE operating mode.
If you want to use pentode mode: Just as a top down estimation you should go to B+ of about 400V, GU50 operated at about 80-100mA . Then you could use your OT with 2K5. Looking to the datasheet you need a bias of about 25V. I would start with Rk of 270 Ohm.

Have a look here http://www.diyaudio.com/forums/tubes-valves/196811-help-these-russian-gu50-tube-amplifier.html (GU 50 SE in Triode mode, this might be a better solution)

Also curious how the B+ was arrived at without a datasheet in the first place;)
 
Here you go:

Gubernator_Mk_6b_3.png
 
Some more

Also curious how the B+ was arrived at without a datasheet in the first place;)

First the B+ was 350V but with a voltage doubler it arrived at 700V :D
Ik is about 55mA at the moment.Ig2 is about 2,5 mA.I just wanted to try it,because i have a bunch of GU 50.I have to say that I use it as a guitar amp,so a certain amount of non linearity is very welcome.As driver tube I use a 6J9P at the moment.
I also tried triode mode but pentode sound is better (and more powerful of cours).Anyway many thanx for your thoughts and of course the data sheet link.
 
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A little confused

Waveborn

A little confused, are you talking about operating a GU50 as a right handed triode with plate to plate feedback or your Pyramid VII push pull circuit with GU50 as a pentode and plate to plate feedback?

Also your link does not work.

A further question if I may, you make reference to the GU50 operating best at high voltages, can you elaborate further on this. Would be much appreciated.
 
Ejam;

if you look at curves you will see why I make reference to the GU-50 operating the best at high voltages. Pay attention at curves bent on the left side, i.e. at higher currents/lower voltages. It is obvious.

Negative feedback linearizes any tube no matter works it in SE or PP amp.

Let me attach the picture here if it does not show for some IP addresses.
 

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Wavebourn

Yes, thank you for pointing out the obvious, but from 400V up the curves are essential flat with little variation. Granted the closer to 400V, a steeper loadline is needed to avoid the lower voltage curvature. What I was alluding too, and perhaps did not express it rather well, was that in several previous posts you recommend 800V. So why not 700 or 600V with a steeper loadline (accepting less power of course) ? Is there something special about 800V or as they say is it a sweet spot for the GU50 ?

Ejam
 
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Ejam;

if you look at curves you will see why I make reference to the GU-50 operating the best at high voltages. Pay attention at curves bent on the left side, i.e. at higher currents/lower voltages. It is obvious.

Negative feedback linearizes any tube no matter works it in SE or PP amp.

Let me attach the picture here if it does not show for some IP addresses.

Is there an IRF equivalent for the mosfet FQPF3N80C ?
 
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