Mesa Dual Rectifier 3 channel bias mod

[henter2017]

Hi, anybody could share some information regarding teh so-called DR bias mod?
The locaiton of the fix resistor as well as the best way and values of pot to use.
I guess using a paralel resistor with the pot will be safer in case contact is lost so the tubes can run to a cold voltage in case of Pot contact failure?
Thanks in advance

[henter2017]

anyone got some info about this mod or recommendations?
I guess for the shake of using any 6L6GCs instead of Mesa (within the range) valves would be pretty useful.

[Enzo]

If you post or link a schematic we can look at, it ought not be hard to determine how to alter the bias voltage.

[henter2017]

should be this one:

http://diy-fever.com/wordpress/wp-co..._rectifier.pdf

is the 3 channel version

[The Dude]

I won't try to talk you out of the mod, but Mesas are typically biased to the cold side and that's part of the "Mesa Sound". I never put Mesa tubes in a Mesa amp (or any other for that matter). Their tube QC is god awful. IME, Mesa amps sound better if you just put good, working, non-Mesa tubes in them without any change to the bias circuit. The cold bias allows a pretty good range of tubes without worry of too much idle current. I wouldn't worry about modding the amp...... Just my $.02.

[g1]

Agree with above.
If you are really intent on doing it, you have to confirm the schematic is correct, as the mesa schematics are 'preliminary' and often do not match the production units.
Please confirm that the bias circuit components (outlined in red) match what is in your amplifier.

[Gregg]

This is a typical Mesa bias configuration. The bias mod itself consist of replacing the 82k (or the 22k one) with a trim pot or a trimpot in series with a resistor in order to avoid too hot bias. The other way is to use a trimpot in place of the 3k3 resistor. This time if you short the trimpot nothing bad is expected to happen. That's it.