Drop out issue with RectoVerb 50

I've been having a strange issue with my ROV 50.
After noodling around for about a half hour, while using both channels back and forth for a couple minutes, the sound just drops out unexpectedly, usually when it's in channel 2. I can hear the guitar just very, very faintly. Right next to silent.
When I switch to 1 and pick soft, it's still gone.
But, if I chop a note or a chord with a heavy attack, while in 1, it comes back to life for a few minutes, until it drops out again.
Could this be the speaker voice coil getting stuck or going bad? Or maybe time to replace the 12AX7s?
Any Ideas?

Update- I tried it with a completely different, newer speaker, and after a half hour of playing, it started to drop out again, exactly as above.
I can rule out the voice coil.

I swapped the 6L6s with EL34s and still the same issue. When it drops out and I flip to stand by, it comes back to volume for a split second and fades out, just like a normal "switch to stand by sound". I wait a few seconds, switch out of stand by, it comes back to life for few seconds, then drops out again!
Tubes seem to glow normally the entire time.
Any ideas before I tear it apart and look for loose things?

Have you tried putting a patch cable in the loop (send to return) to bypass the switching jacks?

It would also be advantageous to clean all the jacks with a good contact cleaner like DeOxit.

I would also try swapping in a good 12AX7, especially the cathode followers (V3 & V4).

99% of issues like this are either bad tubes or dirty contacts.

Dom

Thanks dom!

I will try the first two.
If that don't get it, I'll probably order 5 new 12AX7s, since the present ones are probably the originals, going on 15 years.
I'm suspecting a bad contact somewhere, but the heavy attack bringing it back temporarily, is throwing me.

My Heartbreaker head used to do this all the time. I discovered that it was dirty contacts in the effects loop. These days, if I'm not using the effects loop, I run a short jumper cable in it and will rotate the plugs in the sockets several times before firing up the amp. No more dropouts.

Alrighty then.

I put the 6L6s back in, (already ruled out, and I prefer them anyway) and then did the quicky with the D-5 in all the jacks.
Fired it up, and cut head for about a half hour, then poof!!....drop out.
Turned it off and put the jumper on the FX loop.
Fired it up again, and rode it hard for about an hour, and...she seems back to her kickass self!
Took a break, ran to get some beers, came back and rode it hard for another hour, straight, (that's kinda hard to do at my age really LOL!) and still...no drop out!

dom, you da man!
thunda, hominem quoque vos

Can someone explain, in laymen terms, how this jumper does the trick?

Thanks folks! My next Bud's for you! :lol:

BTW, this was a good exercise in recalling songs in the old memory bank.

Depending on how Mesa made the loop, many of their Send jacks are stereo jack which disconnects the dry connection to the later sections when a plug is inserted. If the contact is dirty, it's adding resistance and cutting that dry connection.