Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: bakerlite on March 16, 2013, 11:46:05 am

Title: bias resisto question
Post by: bakerlite on March 16, 2013, 11:46:05 am

Just wondering if anyone know a good starting point for the bias resistor in a vibrolux reverb (aa270 ) ?
I have no 10k linear pots so i cant use the 10k + 15k resistor as called for in the schematic.
The closest I have is a 25k pot but i am not sure how that affects the range of resistor i should start out with?
I know i could learn by trying out a load of different ones till i get the desired bias voltage and sweep range but if anyone can give a nod as to a good starting point it might save me a few 'attempts'!!!
thanks

Title: Re: bias resisto question
Post by: sluckey on March 16, 2013, 11:56:49 am

10K pot and 15K is the same ratio as 25K pot and 37.5K. So, I'd start with the 25K pot and a 39K resistor.

Title: Re: bias resisto question
Post by: bakerlite on March 16, 2013, 12:04:34 pm

such a gent, thank you.
So it seems the function of the size of the pot only affects the range of the voltage sweep.
And the resistor detemines the ratio? - in this case about 1:1.5.