New Amp(Mark IV), First Post/new member, and I need 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. The noise only reoccurs when I have the Power section on Pentode and Simul Class. On other combinations there is no noise like this.

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!

 

[primal]

Sounds like it "could" be power tubes, though there are many on this board more knowledgable then me on this topic.

As far as I know that switch only alters the power amp side and nothing on the preamp side.

The manual says it reconfigures the circuitry for the two outer power tubes.

Here is something you can try ONLY IF YOUR AMP HAS ALL 6L6 POWER TUBES. IF YOU HAVE EL34'S AS YOUR OUTSIDE TUBES, DO NOT TRY THIS

With the power off of course
Make sure your amp is in Class A mode and in Pentode. Swap the two outer power tubes with the two inner tubes. Mesa for some reason paired them like that. When in class A mode, only the two outer tubes are used.

Then see if the problem has gone away. This way the two tubes that were in the outer socket would now be in the inner sockets and thus not be used in Class A mode.

IF the problem goes away there is a good chance it was the two tubes you just moved to the inner sockets.

 

[TenaciousJP]

Sounds like it "could" be power tubes, though there are many on this board more knowledgable then me on this topic.

As far as I know that switch only alters the power amp side and nothing on the preamp side.

The manual says it reconfigures the circuitry for the two outer power tubes.

Here is something you can try ONLY IF YOUR AMP HAS ALL 6L6 POWER TUBES. IF YOU HAVE EL34'S AS YOUR OUTSIDE TUBES, DO NOT TRY THIS

With the power off of course
Make sure your amp is in Class A mode and in Pentode. Swap the two outer power tubes with the two inner tubes. Mesa for some reason paired them like that. When in class A mode, only the two outer tubes are used.

Then see if the problem has gone away. This way the two tubes that were in the outer socket would now be in the inner sockets and thus not be used in Class A mode.

IF the problem goes away there is a good chance it was the two tubes you just moved to the inner sockets.

Yes, my power tubes are all 6L6's.

I will try it later on when I get back from my lesson/work. I will keep a update with this.

Hopefully it will help!
Thanks
Jordan/TenaciousJP

 

[angelo]

Primal gave you the perfect trouble shooting tip.

The outer two tubes have the Pentode / triode option. So, the best way to see if they are causing you problem in Pentode is to "get rid of them" by putting THEM in the inner sockets and the current inners in the outer - then running class A. If the problem persists in Class A Pentode but is better in Class A triode, then the tubes are out of the equation (probably) and the pentode /triode switch is indeed the likely problem --- though I never heard of that before..

 

[TenaciousJP]

Primal gave you the perfect trouble shooting tip.

The outer two tubes have the Pentode / triode option. So, the best way to see if they are causing you problem in Pentode is to "get rid of them" by putting THEM in the inner sockets and the current inners in the outer - then running class A. If the problem persists in Class A Pentode but is better in Class A triode, then the tubes are out of the equation (probably) and the pentode /triode switch is indeed the likely problem --- though I never heard of that before..

See what the weird thing is, is that the pentode/triode switch works perfectly fine on the class A option with out that noise. And when I put it simul class/triode it's fine as well. just when I put it in simul class and pentode...

I will switch the inner tubes with the outer ones.

Hopefully I will find the culprit.