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-   -   Pentode curves for GU 50 SE amp with 700V B+ (http://www.diyaudio.com/forums/tubes-valves/227805-pentode-curves-gu-50-se-amp-700v-b.html)

usbekhistan 14th January 2013 05:10 PM

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.

jazbo8 14th January 2013 08:58 PM

Quote:

Originally Posted by usbekhistan (Post 3325659)
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

es345 14th January 2013 09:46 PM

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...amplifier.html (GU 50 SE in Triode mode, this might be a better solution)

jazbo8 14th January 2013 10:00 PM

Quote:

Originally Posted by es345 (Post 3326081)
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...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;)

Wavebourn 15th January 2013 12:55 AM

Here you go:

http://www.warpspace.com/photo/tubes...or_Mk_6b_3.png

usbekhistan 15th January 2013 05:42 AM

Some more
 
Quote:

Originally Posted by jazbo8 (Post 3326100)
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.

usbekhistan 15th January 2013 05:43 AM

Sorry
 
Quote:

Originally Posted by Wavebourn (Post 3326315)

Wavebourn your link dosen't work :confused:

usbekhistan 15th January 2013 06:23 AM

funny thing,now it works

davorin 15th January 2013 07:37 AM

Now not working!?

usbekhistan 15th January 2013 08:20 AM

I meant
 
Quote:

Originally Posted by davorin (Post 3326615)
Now not working!?

wavebourns link.The amp is working at all :p


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