KT88 pp triode control grid resistor????

sbcellis · 23rd February 2007, 11:24 AM

Hi
I have a problem.
I have a china amp that i am modding.
It is a williamson copy, but with Kt88 pp as triode and fixed bias.
The second grid have a 2k7 2w to the anode.
Why that big value. Is there a way to calculate that resistor.
B+ is 430 v.
Thanks for reading.
Soren

Tubes4e4 · 23rd February 2007, 04:19 PM

Hi Soren,

when converting a tetrode, pentode or beam power valve as in the case of KT88, to triode, the screen grid stopper resistor should be chosen in values as low as possible, while maintaining that no parasitic oscillation takes place. In your case, a resistor in the range of 100 to 270 ohms should do nicely (but make sure that there are no parasitics anyway).

If you want to learn more on how to convert tetrodes and pentodes back to triode operation correctly, you might have a look at this script.

Regards,

Tom

sbcellis · 23rd February 2007, 04:39 PM

Thank you Tom.

/Soren

sbcellis · 24th February 2007, 03:00 PM

Can you please tell me, why the g2 resistor have to be 2w type.
Thanks
Soren

23rd February 2007, 11:24 AM	#1
sbcellis diyAudio Member Join Date: Apr 2005 Location: denmark	Kt88pp triode controlgrid resistor ???? Hi I have a problem. I have a china amp that i am modding. It is a williamson copy, but with Kt88 pp as triode and fixed bias. The second grid have a 2k7 2w to the anode. Why that big value. Is there a way to calculate that resistor. B+ is 430 v. Thanks for reading. Soren

23rd February 2007, 04:19 PM	#2
Tubes4e4 diyAudio Member Join Date: Jul 2005 Location: Leverkusen	Hi Soren, when converting a tetrode, pentode or beam power valve as in the case of KT88, to triode, the screen grid stopper resistor should be chosen in values as low as possible, while maintaining that no parasitic oscillation takes place. In your case, a resistor in the range of 100 to 270 ohms should do nicely (but make sure that there are no parasitics anyway). If you want to learn more on how to convert tetrodes and pentodes back to triode operation correctly, you might have a look at this script. Regards, Tom __________________ If in doubt, just measure.

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23rd February 2007, 04:39 PM	#3
sbcellis diyAudio Member Join Date: Apr 2005 Location: denmark	Thank you Tom. /Soren

24th February 2007, 03:00 PM	#4
sbcellis diyAudio Member Join Date: Apr 2005 Location: denmark	Can you please tell me, why the g2 resistor have to be 2w type. Thanks Soren

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