#1
I have a Randall RG50TC and a few months ago whenever I would play it, the sound would cut and go really quiet. I quit playing it and today I went and bought new tubes for it, replaced them, and now there is absolutely no sound, except for a buzzing on the overdrive channel
"Waltz it up! The pit is it!"
#2
Have you checked your instrument cable?

Since you have buzzing, that indicates that your power tubes are good, as is the phase inverter. It also would tend to indicate the tubes are good in that channel's chain. It could be an input jack issue. Could be a switching issue inside the amp. Sounds like it's time for a amp technician to take a look, if the simple things aren't causing it.
#3
Yeah, I;ve tried a couple instrument cables that were working on a different amp last night. I guess I'll have to bring it in tomorrow. I wish I was an amp technician
"Waltz it up! The pit is it!"