Mesa Boogie and Tubes

[JoeCon]

Gentlemen,

A friend has a Mesa 50 cal plus, 6L6 powered. He asked if he can put 6V6 tubes in instead. From what I know Mesa's bias while fixed is not adjustable without resistor changes, correct?
Also gotta know plate/screen voltage and current bias voltage so that the tubes don't redplate. The JJs are supposed to be able to handle "higher" voltages. How much?
I know nothing about Boogies...anyone? Bueller??

Thanks.

[Leo_Gnardo]

Gentlemen,

A friend has a Mesa 50 cal plus, 6L6 powered. He asked if he can put 6V6 tubes in instead. From what I know Mesa's bias while fixed is not adjustable without resistor changes, correct?
Also gotta know plate/screen voltage and current bias voltage so that the tubes don't redplate. The JJs are supposed to be able to handle "higher" voltages. How much?
I know nothing about Boogies...anyone? Bueller??

Thanks.

I haven't tried this but there's 2 good things - it "should" work as long as you adjust the bias. Randall Smith would have a heart attack if he knew how many Mesa's I've put trim pots in. Not that I mean him any harm, really. Just trying to do the best for my customers.

Good thing #1 is JJ 6V6 which put up with higher plate voltage than any other currently manufactured 6V6. If you feel like going NOS or UOS, Jim Kelley suggested to me RCA 6V6. Jim made his amps late 70's - early 80's and he's back at it now, working in conjunction with John Suhr, and both are TAG members. Jim's amp runs a quad of 6V6 at nearly 500V on the plates. Takes a tough tube to put up with that.

Good thing #2 is, I've found the 6L6 version of the Mesa 50 cal to be the better one. The 4xEL84 version can be tamed but it takes some modification besides setting bias appropriately.

Some may pitch in that the primary impedance of the OT will be on the low side for 6V6. I don't know what it is exactly, but you can try various loads on the output taps. My general rule is, the combination that yields the most power is the best fit you can get. Maybe not perfect but it will work without overstressing the tubes.

[Firestorm]

The plus models are pretty cool amps. I usually make the bias adjustable. But why 6V6? That's not going to make a noticeable difference in output power, especially with the mismatch.

[Stevem]

The 3rd good thing is that since you need to drop the bias voltage you can likely leave the resistor that's there now in place and just jump it with another!
Your buddy may also like that amp cathode biased which will get that amp much closer to being half the volume that it was if that's more like what he is looking for SPL wise !

With those JJ tubes and that amps plate voltage you are looking to have them idle at 15 ma each, if you do not use a JJ tubes I would drop that down to 12 to 13 ma.