Mesa Rocket 440 and reverb driver tube short life

[stainlessbrown]

I have owned several of these amps, great amps, love em... but they eat the preamp tube (12AX7) that also serves as the reverb driver .... regardless of what tube(s) I've tried, within 40 - 60 hours of operation the tubes go microphonic and the only way to stop the "whistling/ringing" is to turn the reverb intensity all the way down

I've already tried the lower output versions in this tube class (12AT, etc)

I'm wondering if increasing the value of the resistor into the plate (drop the plate voltage) would help

anybody have ideas (and finding schematics for this amp is a real challenge)

[Pedro Vecino]

Reverb circuit is this amp is made with a 5532 integrated circuit. The 12ax7īs work with standard voltages and gains. You must find a tube well protected against microphonics (Sovtek 12Ax7WC is a good choice) and if necessary trim the spring of the metal shield to reduce pressure including a piece of foam.