What Is Wrong With My Mark IV Compact Combo?!?!?!?1 HELP!!!!

[TenaciousJP]

Hi there,

My name is Jordan, other wise known as TenaciousJP on the forum name. This is my first post ever made too.

Anyways, three days ago I got a Mark IV compact combo. And I've noticed a problem with it.

It has to do with the Triode and Pentode switch. When ever I turn to Pentode all the channels go out of whack making all these buzzing, flopping noises. But when in Triode...it's fine a little back round buzz on the lead channel, but that's normal with every tube amp.

Anyways, I have no idea what's wrong with it. I have it in Tweed Mode, Harmonics, and triode(because that is the one that doesn't make any noise)

I spent all my money on this, and have no money at all at the moment. If someone can assist me with this I would extremely appreciate it very much!!!

Thanks
Jordan/TenaciousJP

P.S could it possibly be the power tubes? or???

Thanks again!

 

[Tuna141]

Here's a potentially inexpensive fix you can try: Your problem may simply be a bad preamp tube. Buy a spare 12AX7 (around $15 or so) and then try swapping it, one by one, with the preamps in your amp. If the problem goes away, then one of the tubes was bad.

Good luck.

 

[TenaciousJP]

Here's a potentially inexpensive fix you can try: Your problem may simply be a bad preamp tube. Buy a spare 12AX7 (around $15 or so) and then try swapping it, one by one, with the preamps in your amp. If the problem goes away, then one of the tubes was bad.

Good luck.

I doubt it's a preamp tube.

It only makes that horrible noise when I have it running Simul class and pentode at the same time. Other combinations it's fine.

So it's more likely a Power Tube.

Also last night I removed all the power tubes and saw one of them was missing the plastic center part between the tube progs...while the others had theirs. I'm not sure if that maybe the problem?

 

[Tuna141]

Yeah, I agree. For some reason I was thinking that the Triode/Pentode affected the preamp tubes (I should avoid posting early Monday mornings in the future ) - daah.

I agree the that the problem is more likely related to the power amp tubes. Good luck.

 

[Thrashman]

Have you tried flipping the ground switch and tried all 3 positions to see if that helps?