It's Baaaack! Mike Christenson, ace Mesa certified tech operating out of House of guitars in Salt Lake City figured out a foolproof adjustable cathode bias system, a combination of two resistors, one parallell, other in series with an Ohmite brand rheostat. The range is very limited, such that minumum is not too cold and maximum is not too hot, slightly less hot than the stock setting, which might have been OK for tubes available in the early 90's when the amp was made, but not necessarily the best for right now.
The rheostat is mounted right in the back of the chassis, and has a knob to turn either direction from outside the amp, so no need to take the chassis out. Simple and elegant. If I want to check, I can still use a dual socket biastool connected to my DVM to take readings. It was allowed to run for an hour and no heat buildup was noted for the new parts. A few caps were replaced, it's running quiet as a church mouse now. The new power tranny was a drop in fit for the old one, the exact part number for the old one is no longer available. Finally, modded the f/x loop to serial from parallell, and easily reversible. With a twist of the dial, can tell a slight difference in tones from colder to hotter bias. Then there's the SS rec setting still available for more juice if needed. The Russky mil stock 6p14p-ev power tubes were operating at new levels of current draw still, after close to a thousand hours of operation, too. Guess that when they said they were rated for 5000 hours in circuit they weren't kidding!
Saweeeeeet!
