2:90 Cant see whats going on . . . .

[Cedrik Menard]

This is my second Mesa 2:90 and I think its a great power amp. Nothing to say about tone. But my actual unit is doing something strange on channel A and its about 2 1/2 months old. about 5-10 min. after I turned from stdby to ON, I hear some weak intermittent crackling/scrathching. Volume and Presence controls have no influence on this, no matter how I set them. I tried to swap the preamp tubes around inside but couldnt noarrow it down but its hard to tell since I had'nt a new tube around, I was just switching tubes betwen them. I also tried to tap lightly on the preamp tubes but it didnt seem to change anything. I am really upset becaus its an almost new amplifier. Can someone give me advice please?
Did this happen to some of you yet? Thanx for help!

 

[Tuna141]

Most likely it's a tube problem - either preamp or power amp. I'd definitely try swapping in a new tube to see if the problem goes away (I'd try 12AX7's first - they're only about $8, then move to the power tubes if that doesn't work - I'd also try tapping the power amp tubes lightly to see if any of them arc or you can hear an audible crackle).

Other simple things to try - re-seat all the connectors (may be some oxidation on the pins or may have become unseated). Also try reseating all of the tubes (could be oxidation on tube sockets).

AS ALWAYS, BE CAREFUL WHEN WORKING INSIDE OF AMP - LETHAL VOLTAGES ARE PRESENT!

Good luck

 

[Timbre Wolf]

Well put, Tuna. It definitely sounds like a tube issue to me, too, and I couldn't have said it any better than T141!

- T