O/T Power Tube Biasing

[ildar]

Is it possible to rebias a fixed-bias power amp (Mesa/Boogie) so I could change from 6l6s to el34s?
Is it something I should attempt myself?

[Lonestarjohnny]

you might want to check with Mesa on that, and make sure your transformer can handle the extra amperage draw that the 34's need to operate properly, if they say sure then it's O.K.
But if your not use to working on tube amp's this would not be an easy job for the unqualified.
Johnny

[R.G.]

Go to GEO and check into the Tube Amp section. Read the Tube Amp FAQ.

(a) yes, you can rebias for 6L6 -> EL34
(b) it may or may not be an audible difference in sound, depending on the amp
(c) EL34's use a lot more heater current. Your power transformer may or may not be able to cope.

[cd]

Should you try it yourself - OK, not to sound like an ***hole, but if you don't know what it takes to rebias for 6L6>EL34 (or the tonal change - what amp are you using?  It could sound horrible) I doubt you want to be poking inside a live amp with killer (yes, LETHAL) voltages inside.  Bring it to a good tech!

[The Tone God]

Glad someone pointed out the heater curent. Thats a point overlooked quite often.

Another issue not mentioned yet is how pin 1 is handled on the tubes. 6L6s do not have/use pin 1 where as the EL34 does. I don't know if the amp in question takes care of that but since it is specificly designed for 6L6 I would doubt it. You would need to deal with that which can be tough since from what I remember the MESA amps are PCB construction.

This is not just a simple "change one resistor" job. I would have to add myself to the "if you need to ask maybe you shouldn't" group. Sorry.

Andrew