Hello!
I was in the thoughts of modding my valveking head to be able to adjust the bias. By looking at how it´s done on the 5150 model I came to the conclusion of replacing resistor R250 in the attached schematic. Can anyone with knowledge tell me if this is right? What value of the trimpot would you recommend? In series with a safety resistor if the pot goes bad? I haven´t checked the bias value unmodified and I don´t know the B+ voltage either. The resistor is 39K and I belive this gives a fairly cold moderate bias.
Thank you.
Chris.
If the schematic comes out blurred, magnify it!
Valveking Mod to adjustable bias.
Moderators: pompeiisneaks, Colossal
Valveking Mod to adjustable bias.
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skyboltone
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Re: Valveking Mod to adjustable bias.
measure the voltage there and let's know what it is. I suspect you'll want to replace that resistor with somting like an 80K then parallel it with a 10k pot and a 68k resistor in series. Ground the wiper of the pot. That's gonna get you from where you are now to points higher but not lower.
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Seek immediate medical attention if you suddenly go either deaf or blind.
If you put the Federal Government in charge of the Sahara Desert, in five years time there would be a shortage of sand.
Re: Valveking Mod to adjustable bias.
Size the pot to as close to twice the resistor value as you can. Liner taper would be the best.
Wire it up as a variable resistor.
Set it to about 1/2 way to start. Adjust to taste from there.
If the pot fails it will drive the bias voltage to it's most negative ("cold") value.
Good luck,
Dave O.
Wire it up as a variable resistor.
Set it to about 1/2 way to start. Adjust to taste from there.
If the pot fails it will drive the bias voltage to it's most negative ("cold") value.
Good luck,
Dave O.
Re: Valveking Mod to adjustable bias.
most exellent guys...I´m so lucky to have ya all!
Thank´s a million!
and Merry XMass to U!
Thank´s a million!
and Merry XMass to U!