Help me brainstorm a tube problem on my Mark V

[scoden]

I was playing in channel 3 10 watts at home ..kiiler tone when suddenly volume started fading in and out to almost zero and back.....no changess in the glow from all 4 MESA EL34s. Happened in all 3 channels as I switched to see. I put amp in standby and when I did..I saw a quick flash come from behind the amp. The power tube nearest the Rectifier tube looked like it blew as the glass at top of tube looked burnt...no smell or smoke.

So seems straight forward....I then put the amp in 45 watt mode channel 3 and proceeded to play with only two inner tubes in as I have no replacements yet.

After an hour or so I got the same volume drop / fade in and out ...no change in how tubes glowing. I just shut it down.

Any suggestions on what to do.....pre amp slot that may be the offender....I plan on getting alll new power tubes. I love the EL34....but Ive had so many premature tube failures with EL34s I may just geth 6l6s again ( they seem more robust).

Thanks for any insight.

 

[scoden]

Just an update ...swapped out v7 only with another mesa 12ax7 and left only two el34 in middle on 45 watts ...played for 2 hrs no volume fading.

To be continued...

 

[Boognoob]

Well glad to hear you sorted that...!!! Tubes, eh...? :lol:

 

[scoden]

not quite yet...started to do it again.....this time I just changed all power tubes with new el34....put a 12ax7 sp in v1 and reg mesa 12 ax7 in v3.

Did it again....ugh.

Last try I put in a new mesa rectifier tube I had as a spare ..so far so good.

to be continued....next Im playing acoustic from now on...jk

 

[scoden]

So with all I did so far, this am I had some volume fading again...I switched out of channel three and it seemed to stop but perhaps it was a coincidence. Its so sporadic.

So next I put in a new 12ax7 in v4 had a Chinese penta in there...I also sprayed some contact cleaner in effects loop and cab jacks.
Played it for a few hrs...so far so good.....at least the tone and dynamics are improved with all the new tubes.

Im running out of tube options ...only ones I havent changed so far v2 v5 v6 ...v2 doesnt seem to be a highly likely culprit

And the story continues...


Anyone one else who has had this ....am I overlooking anything?How did you solve your issue?

 

[yeti]

check your power at the wall...

is it periodically being reduced due to a furnace, or some other item on the circuit pulling harder on the electrical load?

light dimmers in some other part of the house? wife running the blow dryer?

 

[scoden]

Just updating a bit ...so far with about 6- 8 hrs on the amp after switching out v4 and spraying loop and speaker jacks,I havent had an episode of volume fading.

Maybe this will help others who might have this happen to them.