Mk IV (Rev A) Reverb problem

When I turn up the reverb control any amount, the signal gets all nasty, farts out and sounds crappy. All the tubes in the amp were replaced about 4 mos. ago. I tried a new 12AX7 in V3 & V4, but no change. I don't usually use much if any reverb, but decided to start using it again, that's when i found the problem. It's basically sounding like turning the reverb knob is adding huge amounts of gain to the signal and overloading it.

There is nothing else connected to the amp other than the guitar. The problem is most noticeable on CH1 & 2, it is masked more (but still a problem) on the lead channel due to the gain.

The reverb driver is a 12AT7 for a "revision A" MKIV and is V4.

boogietone said:

The reverb driver is a 12AT7 for a "revision A" MKIV and is V4.

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yeah, that's what I had in it, --I just swapped it out w/ a 12AX7 that i have for a spare because it was new, but the problem is still there with either tube. thanks for the input.

I think I might have had the same problem, swap the cables on the reverb tank, in other words they might have been hooked up backwards.

Force said:

boogietone said:

The reverb driver is a 12AT7 for a "revision A" MKIV and is V4.

Click to expand...

yeah, that's what I had in it, --I just swapped it out w/ a 12AX7 that i have for a spare because it was new, but the problem is still there with either tube. thanks for the input.

Click to expand...

sounds like dirty reverb tank connection's.. clean them with metho or electical contact cleaner to get rid of the dirt of what ever has build up on the socket's..

Tom

Shep said:

sounds like dirty reverb tank connection's.. clean them with metho or electical contact cleaner to get rid of the dirt of what ever has build up on the socket's..

Tom

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okay, i'll give that a try tomorrow. i appreciate it!

Like i asid also make sure you didnt reverse the reverb tank jacks, because I had that problem.

Force said:

Shep said:

sounds like dirty reverb tank connection's.. clean them with metho or electical contact cleaner to get rid of the dirt of what ever has build up on the socket's..

Tom

Click to expand...

okay, i'll give that a try tomorrow. i appreciate it!

Click to expand...

okay. i did switch the jacks and it didn't seem to make a difference. One thing i may not have mentioned in my previous posts here is that when I turn the reverb up i get a tremendous volume/gain increase. :? the jacks don't look dirty, but i am going to pick up some electrical contact cleaner and try that anyway.

HI, don't know if this helps, but recently after repairing my reverb tank I had the same problem. On a whim I changed the RCA cables from the chassis to the tank and it subsided. Not sure if you've fixed it by now, but it definately worked for me.

I was having the same problem with my reverb. When I turned it up to 2 I would get a buzz and an increase in highs and gain. Mine is a class B, so I don't have the one dedicated reverb tube.
I saw a post about switching the RCA connections, that they may be reversed. I had never had this amp worked on, had bought it new, and don't know of any reason they could have been switched.
As a last resort prior to taking it to a service tech, I switched the wires at the head and this worked! No more buzz, and I have a new, much better amp!

Buy a new tank!

I've replaced the tank in my IV twice now, sometimes the tiny wires on the transformers inside the tank break due to movement.

New tank is only about $40 or so.