don't use the footswitch and ext control jacks together

[gtrnstuff]

The manual on page 40 simply says that the external control jacks will override the footswitch, it doesn't say don't have them both plugged in at the same time.

I called MESA tech support when my Mark V head stopped passing audio in channels 1 and 2. Still works in channel 3.
Gary said you use either the footswitch or the control jacks, not both.
That's what fried my channel switching.

My head is still under warranty but still I have to ship it off to get fixed.
Would have been nice if the manual had a big warning about this.

i was using both because I wanted my Bradshaw switcher to do channel switching, but still wanted to be able to turn reverb and FX loop on and off, and the Mark V doesn't have control jacks for those functions.

 

[OldTelecasterMan]

Wow... Good information....

 

[HCarlH]

Sorry it happened to your amp. Thank you for the heads up.

 

[gtrnstuff]

Follow up. Got a call yesterday from the tech at Sweetwater.
Working fine with its footswitch. Not acting odd at all. All channels working.
The day I sent it, 05/14/2015, it would only pass audio with channel 3 selected.

Other than being a really complicated amp depending on lots of old- style diode logic and relays that all have to work, and possibly from being powered down for a week or so, so it could sort of re-set itself, the tech had no good guesses.

I just love stuff like this.

 

[gtrnstuff]

The amp is back, all 3 channels work as they said.
I notice they are all set to 90w.
I usually run channel 1 and 2 in 45w tube rectifier.
I switch ch 1 to 45w. It crackles and goes dead.

I replace the dead rectifier tube.

All is well.
D'oh. I should have caught that.
But the techs didn't catch it either.
Expensive lesson in "if you haven't checked everything, you shouldn't assume anything."