Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: ernie_jr on August 07, 2012, 02:18:48 pm

Title: power rail question
Post by: ernie_jr on August 07, 2012, 02:18:48 pm

I am looking to build another sunn 200s amp but want to add a second preamp (from an Ampeg B15) On the power rail the last resistor is 33K, if I remember correctly, by adding in another 12ax7 I should make the resistor around 16K to keep the voltages correct. Let me know if I am heading the right way.
Thanks,
Ernie

Title: Re: power rail question
Post by: Iannone on August 07, 2012, 03:33:34 pm

That's right.  Ohm's Law - when you double the current (two tubes), you need to cut the resistence in half to maintain the same voltage drop.

Title: Re: power rail question
Post by: sluckey on August 07, 2012, 03:49:23 pm

If you do it like this it will not affect the voltages for the Sunn. All you need to do is pick a value for Rx that gives the voltage needed for the Ampeg.

Title: Re: power rail question
Post by: ernie_jr on August 07, 2012, 08:28:31 pm

Sluckey,
Thanks taht will work great. The ampeg (if taken off a b26) has about the same voltage as the sunn, so I can just use another 33K
Thanks again,
Ernie