Major Mark IV lead channel issue

[spirit7]

Hi All,

My Mark IV's lead channel has started being funny.

There is a constant, noisy hum in the background when playing, and if I turn the master volume up past 2 it descends into a high-pitched squeal!

I replaced the V5 preamp tube and it doesn't seem to have helped the problem. All the other channels are fine.

Could it be the power tubes? They haven't been replaced since 1995

Thanks in advance,

-C

 

[dodger916]

You need to replace V3 or V4. V5 is the phase inverter/driver, and is more involved with the power section (global) than the preamp section. Here's a link to the manual. Look at the Tube Task Chart on Page 17.: http://www.mesaboogie.com/manuals/Mark 4.pdf