Bias caps??

[kdove]

A few months ago I replaced the old filter caps in my Mark 1. At the time, I ordered two of the smaller caps (bias caps I believe they are called) while placing the order.

I did not replace them because:
- These caps looked good and reportedly were low risk.
- They were also wired in with other components making it more difficult (but not impossible) to replace.
- Think they are 50uf/75V ... see mirror replection (could only locate 50uf/50V Sprague Atom replacements)

I can replace them ... my questions:
- Any concern in using these lower voltage replacements?
- What is the risk for not replacing them?
- What would defective bias caps cause in the sound of the amp ... what should I listen/look for?

Thanks in advance

 

[Boogiebabies]

Ken,

Mesa now uses and recommends using 47uf/100V. Going to a lower voltage is not advisable. They do not effect the tone, but if they fail after 30 some odd years they can take out your tubes and possible your OT.

Looking at the schematic, the Blue/Red tap off the PT goes to the board, reversed diode and then to the dropper resistors and then resistors and caps in series. The blue wire coming off the middle should go to the power board and then to four 2.2K resistors to pin 5 and should read around -52V.

 

[kdove]

Thanks BB ... I'll look around.

 

[Boogiebabies]

Thanks BB ... I'll look around.

I just added a bit more to my original post.

Sorry the Panthers are moving the ball.