Mark IIB Problem. Buzzing (not hum) coming from chassis...

[junebughunter]

Ok, this isn't my amp but it's my room mates.

He has a Mark IIB, good condition, newer tubes (we swapped out all the pre-amp tubes).

One day while we were jamming he switched on his lead channel (pull switch) and it didn't worked, it was as if it was still on the clean channel but the amp was making this weird buzzing sound. Kinda like fluorescent like makes when it first turns on.

We took it apart and sure enough (we haven't completely pin-pointed it) the sound seems to be coming from a little blue box with a clear top and what appears to be some copper inside sitting just behind the pull out switch. I don't see any visual indications of where the sound or problem is coming from.

Things we tried:
We've tried using a footswitch, same problem.
Swapped out pre-amp tubes.
Did a somewhat thorough visual inspection.

The sound comes out even if the speaker is not plugged in.

So anybody have advice on what this could be?

 

[BPski]

Sounds like you have a bad relay. You can get them right from Mesa or even Mouser. They are inexpensive and relatively easy to replace. Any decent local tech could do it. Hope this helps!

 

[junebughunter]

I can't find a similar relay on the mouser site, any clues or info?

 

[BPski]

I got a replacement direct from Mesa. Give them a call.