Mesa Quad: Channel B output going bad

[krcassid]

My Mesa quad is starting to crap out on output B. Output A is fine. It is (somewhat) intermittent. But, when it starts to go, it gets nasty: bad breakup, volume cutting to near 0...

My natural assumption was "tube". But, I sat there and replaced each tube, one by one, with no love. Anybody got any ideas?? Is there a tube (or 1/2 a tube) that is specifically for output B?

It may be time for a trip to Petaluma anyway. The reverb is SUPER noisy. Is this common or do any of the rest of you have quiet reverb?

Thx!

 

[krcassid]

OK. Just got the answer on another post. Swapped V22 and output B OK so far.

Any hints on noisy (too much so to be useful) verb?

 

[crane]

Same thing, bad tube (V24) ?

 

[krcassid]

Same thing, bad tube (V24) ?

Thx! Can you identify location of V24? The schematics confuse me and I don't have a proper tube layout diagram. The other post identified V22 as "second from right in the back row as you look at the amp from the rear"

Thx!

 

[crane]

 

[krcassid]

Fantastic! Thank You!

However, new tube in 24 did not help noisy reverb

Does anybody out there have a quad with quiet verb? I may be chasing my tail...

Marcus at MB also sent me this today:

Quad Preamp Tube layout

V11-input for channel 2
V12 Channel 1 and channel 2
V13 Lead for channel 2
V14 EQ & reverb mixer

V21 Input tube for channel 1
V22Effects return & output
V23 Lead for channel 1
V24 Reverb driver & return