Mark IV no sound

[tim6string]

I power on my amp, take it off standby and I have sound for a very short time (< minute) and the the sound cuts out. I still have lights and the tubes are glowing normally.

If I power it off and start over it does the same thing.

A few weeks back I used contact cleaner on the power switch and cleaned the effects loop send/return (based on threads I searched.

It seemed to work fine not a single problem for about 4 hours playing time, now the problem is back.
Any thoughts?
Time to go to the shop?

 

[sduck]

Try changing tubes - sounds like one has gone bad. They can be bad and still be lit up at the same time.

 

[tim6string]

Try changing tubes - sounds like one has gone bad. They can be bad and still be lit up at the same time.

Do you really think it is tubes? I have some to try and it is certainly a valid trouble shooting step. There is even some evidence to support it, I did recently change tubes, I am guessing 20 hours of playing time and did not have the problem with the old tubes.

There is a very faint pop like a circut shuts off when the sounds stops. The pop doesn't concern me, it is not loud just the best description I can come up with. So it is like something is shutting down. And a power off causes it all to work again briefly.

 

[tim6string]

Ok, figure this out. After spending about an hour or so trouble shooting here is what I know.
If I spray contact cleaner in the switch and toggle it back and forth then power it on, it will work fine.
If I then power it off and back on it is back to cutting out shortly after power it on.
Power it off, toggle the switch up and down (unplugged) power it back on and it works fine.
Repeat, repeat, repeat.

Really seems to be related to the power switch.
Make any sense to anyone? Anyone seen this before?

I am going to call Mesa tomorrow (not sure if it is Monday or Friday they are not in)
I am also calling my amp tech.
Can't live without this amp!

The gig on Friday with my back up was killing me.

 

[sduck]

It could be a bunch of things. I just suggested the tubes because it's something easy to try and see if it makes a difference. The more I think about it the less I think it might be the tubes though.

 

[tim6string]

It is weird, I will make a few calls tomorrow. I will post if I figure something out.

 

[tim6string]

Try changing tubes - sounds like one has gone bad. They can be bad and still be lit up at the same time.

You called it! (Thanks for the advice)
That is so weird that cleaning and toggling the switch seemed to fix the problem, seemed like a direct correlation, although I will agree it made no sense. I talked to Mesa and my tech and they a little baffled but thought tubes or something bigger.

Turned out to be V2 preamp tube.
Odd note. My MK IVa manual does not have the tube positions documented and the (assuming) MK IVb manual on the Mesa site has the V1 - V4 in the exact opposite order of mine. My shielded tube is on the other end. It was the tube next to it, which appears to be the 3rd gain stage for channels 1 & 2 and the 5th gain stage for channel 3.

Anyways, I put in a new tube, power on and off a bunch of a bunch of times and it worked great. This is probably the one time I would have bet against a tube issue.

Great to have my amp back, IMHO it is the greatest sounding amp!

FYI, Mesa support also mentioned cleaning the fx send/return with contact cleaner which I did the first time (because I read it on here) seems that is very much a known issue.