Does my Marshall MB-150 need a new pre-amp tube, or is it worse?
I have played through a Marshall MB-150 for about the last 3 years. I bought this used, so I don't know how old it is. I have loved this amp until now.
The Classic Channel supposedly uses a 12AX7 pre-amp tube.
When playing through Classic channel, as I am wont to do, if I turn the gain & volume up to live band-type levels (about 12 Noon on both volume and gain knobs), my signal will infrequently distort or break up (not in a good, fuzzy way, but in a loss-of-signal-sounds-like-thunder-in-the-distance kind of way). At first I thought I blew the speaker, but after further review that is not the problem at all.
I suspect the tube because the Modern channel, which does not employ the tube, produces no such issues. I can turn it up loud, even with a Sansamp DI cranked up and no problems.
There are no other signs of bigger issues like bad caps, no scratchy or crackly pots or anything.
I'm a total amateur, and would appreciate any wisdom on this. Including how & where to change the preamp tube.