Mark IIC+ bias question

[metalmarlon]

I have a very reputable amp repair facility that can put a bias adjustment knobs on my Mark IIC+

This would be good becuase then I can use current production tubes to their fullest potential. And not have to rely on finding NOS tubes that are of the amps era to make sure it bias's up correctly.

How would this affect the value of my Mark IIC+?

Should I do it? I have been told it is more like an investment in the amp. But I want to hear more opinions.

 

[JOEY B.]

Should I do it?

If it was mine (and it almost was :wink: ), I would have the bias resistors on the outer tube sockets put back to stock specs. The plate voltage should be in the 450-460 range and the bias should be -46 for the inner pair and -37 for the outer pair measured at pin 5 of the tube sockets. Then spend a little money for a good current draw/plate voltage meter (Weber Bias-Rite or similar). I don't think that you will have any problem finding new production tubes that will bias correctly, if you give the tube vendor this information. Whatever you do, don't drill extra holes in the chassis for any bias mods. That would have a negative impact on the value of that amp, for sure.

 

[Boogiebabies]

I would leave it alone. It's a paint to balance the inner and outer pairs anyway.
A small turn on the pot may be great for the inner 6L6's, but too much for EL-34's.

As for JB's comment on the 10K's added to the outer sockets 220K's, remove them.
Who knows what they are doing to your preamp signal.