Pentode curves for GU 50 SE amp with 700V B+ - diyAudio
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Old 14th January 2013, 05:10 PM   #1
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Default Pentode curves for GU 50 SE amp with 700V B+

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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Old 14th January 2013, 08:58 PM   #2
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Originally Posted by usbekhistan View Post
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/f...018/g/GU50.pdf
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Old 14th January 2013, 09:46 PM   #3
es345 is offline es345  Germany
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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 Help with these Russian GU50 tube amplifier (GU 50 SE in Triode mode, this might be a better solution)

Last edited by es345; 14th January 2013 at 10:05 PM.
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Old 14th January 2013, 10:00 PM   #4
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Originally Posted by es345 View Post
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 Help with these Russian GU50 tube amplifier (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
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Old 15th January 2013, 12:55 AM   #5
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Here you go:

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The Devil is not so terrible as his math model is!
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Old 15th January 2013, 05:42 AM   #6
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Default Some more

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Originally Posted by jazbo8 View Post
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
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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Old 15th January 2013, 05:43 AM   #7
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Originally Posted by Wavebourn View Post
Here you go:

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Wavebourn your link dosen't work
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Old 15th January 2013, 06:23 AM   #8
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funny thing,now it works
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Old 15th January 2013, 07:37 AM   #9
davorin is offline davorin  Croatia
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Now not working!?
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Old 15th January 2013, 08:20 AM   #10
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Default I meant

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Originally Posted by davorin View Post
Now not working!?
wavebourns link.The amp is working at all
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