#1
This was really strange...last band rehearsal I did the amp worked fine for something like 2 hours, then suddenly the gain dropped to about half, more like crunch and didn't change. I kept playing as I had to finish through.
Next day - amp is fine, left it on all day and occasionally checked it - no problem, tone didn't change.
Any ideas? Maybe heat protection kicked in, or?

I guess I will have to see if I can replicate the issue but again, I rarely get to do a 3hr set at normal volume, mind you it wasn't extremely loud, I crank it louder when I record. Only other thing I was thinking maybe some kind of electrical current draw as we had a lot of stuff plugged in and the house is built in the 60s so the electrical wiring is a little behind the times.
#2
It may be the 12AX7s, but I'm sure you're already onto checking them. One of them may go microphonic soon - my guitar teacher's Vox AC30 did the same on a crunch tone going clean for a couple of hours, and then a week later he had a microphonic 12AX7. Sorry for the lack of experience apart from that.
The above post is in terms of 'YMMV' and 'IMO', etc...

Quote by Offworld92
This debate is exhausting to read.
The guitar world is drowned in fairy dust.
We need to start at the very beginning. What is tone.
#3
Roll a new 12AX7 through it. You'll have to do it while it's hot so be careful not to burn yourself.
Gilchrist custom
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Marshall 18W clone
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Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
#5
That would be the quickest solution. However, it won't tell you which one was faulty so you are gonna be throwing away a lot of good tubes.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
#6
Yeah, you're right. But now I have to wait for 2 hrs for the issue to manifest itself

Maybe I'll just start bringing spare tubes at rehearsal and change one after the other...or maybe the pencil tap trick will show the culprit.
#7
this is a long shot, but have you checked the footswitch? maybe switch the channels with and without it.

pencil test, and maybe clean out the sockets, etc.
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nope i am "GOD of the guitar forum" i think that fits me better.


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youre just being a jerk man.



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#8
Quote by trashedlostfdup
this is a long shot, but have you checked the footswitch? maybe switch the channels with and without it.

pencil test, and maybe clean out the sockets, etc.


Footswitch? What do you mean? I disconnected all the gear and fx plugged into it, and switched manually, still the same thing. It was switching channels with no issues, the distorted channel sounded like aggressive crunch though, like it dropped gain about 50%.
#9
Try calling Mesa's support, especially if you purchased the amp new through an authorized reseller. Only heard good things about their support and they took care of my buddy's M9 bass head.
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Peavey Vypyr 30
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#10
Quote by diabolical
Yeah, you're right. But now I have to wait for 2 hrs for the issue to manifest itself

Maybe I'll just start bringing spare tubes at rehearsal and change one after the other...or maybe the pencil tap trick will show the culprit.
That's how I'd do it.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
#11
Sorry for this if it is a necrobump (btw how come noone has made a death metal band with that name?)...

So, I had another rehearsal and this time it was at full blast for about 3 hours and had no issues whatsoever. Weird...Maybe bad power?
That'd be surprising cause the rehearsal room had such a shoddy power - we were picking up Mexican radio via our amplifiers when on the gain channel