mark 5 -squeal/uncontrollable noise

[K-Roll]

Hey guys

I thought I might just ask here for some ideas. The thing is that my mk5 really squeals a lot even though I've been using a NS2 in front of the amp. It mainly does on Ch3 and sometimes on Ch2 (on ch2 only if set to full gain but that would be normal i guess). What bothers me is the ch3, i just can't play staccatos or mute my strings. I am not even using any brutal settings related to gain/trebles/GEQ, in fact I've got my gain and trebles both around 1oclock and most of my GEQ trebles are set to the middle line (maybe a slight bit higher)
Is this normal?
I am using the amp on hard bypass mode. pentode, MK4 setting, GEQ engaged
I suspect it might be a V1, but should I really look further for more preamp tube spots? The thing is the MK5 is such a piece of **** to work with, you can't change tubes quickly if needed and I'll have to open the chassis and drag it out..

 

[domct203]

I uderstand how much of a pain it is to get to the preamp tubes in the MKV Head. It's sort of a blessing for me though, it keeps me from excessive tube rollin'! :lol:

Looking at the Tube Task Chart on pg. 62 of my manual it appears that the only tube that doesn't affect CH. 3 is V2.

I would rule out the PI (V7) for now.

Both V1 and V3 affect Ch's 2 & 3 Gain Stages. V4, V5 & V6 are the final Gain/Drive Stages for Ch. 3 as well as global Reverb & FX Loop Drivers.

Ch. 3's primary Gain Stages are V1A->V1B->V3A->V6A.

IMO I would pull the chassis and trouble-shoot tubes only after I troubleshot everything external to the amp. Does the amp "squeal" when it's just your Guitar straight in, no effects? Any change with switching in the Hard-Bypass of the FX Loop?

Good Luck,

Dom