Dual Rec volume drop question

[braf ssb]

Hey y’all, my rev f dual rec has been going through some weird volume drop issues. Initially i assumed it was power tube failure but i put some new 6l6s in it and the same thing happened again. Wondering if anyone has any guidance? Only trying to avoid bringing it to a tech if possible cuz I’m moving out of state in a few weeks, but let me know what you think - it happens towards the beginning of the clip
Also it made a crazy loud pop when i flipped to standby at the end if thats useful info



Secondary question if anyone can/wants to answer while you’re here; whats up with the 8/16 ohm inputs on the rev f, are they really just both or whats the deal with that?

 

[Eevil]

Howdy

Does it happen with fx loop disabled? (Not sure if it’s possible in rev f )

My first suspects with intermittent dropouts would be:
- fx loop jacks (dirty)
- bad guitar cable/jacks
- speaker cable/jacks
- dirty tube sockets
- bad tube(s)

Check everything around the amp and if the issue persists then maybe it could be time to consult proper Mesa tech

 

[tbonesullivan]

Secondary question if anyone can/wants to answer while you’re here; whats up with the 8/16 ohm inputs on the rev f, are they really just both or whats the deal with that?

Mesa amplifiers are pretty tolerant of impedance mismatches, so those outputs can be used with either 8 or 16 ohm loads. Mesa later added a separate tap for the 16 ohm load, probably because people wanted an exact match for their 16ohm cabinets, which is the standard impedance for most marshall cabs.

 

[CoG]

both mine and my buddy's tremoverbs had dropouts related to a big resistor near the PI (sorry, I'm not a tech, I can't tell you which one) that had drifted over time (it's been 30 years...) and was heating up and causing a trace to lift. another friend had the same thing happen on his roadster. literally exactly like in OP's video, drop in volume with no change in tone.

 

[braf ssb]

Checked to make sure it happened with the loop disengaged(took a little longer but it did) and it looked like a tube was going crazy too. Def gonna have to bring it in its lookin like.

both mine and my buddy's tremoverbs had dropouts related to a big resistor near the PI (sorry, I'm not a tech, I can't tell you which one) that had drifted over time (it's been 30 years...) and was heating up and causing a trace to lift. another friend had the same thing happen on his roadster. literally exactly like in OP's video, drop in volume with no change in tone.

yeah i had seen someone else talking about a similar issue and was hoping it wouldnt end up being that lmao

 

[domct203]

Have you tried changing preamp tubes? Volume drop out can be caused by a failing preamp tube, especially in cathode follower use, which is V3 & V4 in your amp.

Mesa’s current 12AX7 is a JJ ECC83 and is safe for cathode follower use as well.

Read here:
https://boogieforum.com/threads/did-you-get-the-memo.25102/#post-186780
Dom

[edit] I should have looked at your video before posting, those two tubes red plating like that is a serious issue that needs a tech. Don’t continue to use the amp like that.

 

[tbonesullivan]

Oh damn, yeah you got some problems that require professional attention. It's unlikely that two tubes would decide to red plate all on their own.

 

[GJgo]

Mesa amplifiers are pretty tolerant of impedance mismatches, so those outputs can be used with either 8 or 16 ohm loads. Mesa later added a separate tap for the 16 ohm load, probably because people wanted an exact match for their 16ohm cabinets, which is the standard impedance for most marshall cabs.

It's really a pair of 8 ohm taps. Even though it can handle a 16 ohm load it always made my OCD twitch that they labeled it that way.

 

[tbonesullivan]

It's really a pair of 8 ohm taps. Even though it can handle a 16 ohm load it always made my OCD twitch that they labeled it that way.

True. The way they label the outputs on the back of some Lone Star Specials is even MORE OCD inducing. The two 4 ohm jacks instead say "MAIN OUT (For 30-15-5 Watts)", and to the 8 ohm jack to the left of that is "OPTIONAL (For 35 Watts).".

 

[Eevil]

Checked to make sure it happened with the loop disengaged(took a little longer but it did) and it looked like a tube was going crazy too. Def gonna have to bring it in its lookin like.

yeah i had seen someone else talking about a similar issue and was hoping it wouldnt end up being that lmao

Yep.. better to drop it off to a tech - who is no Mesa hater
red plating is usually sign of a bigger issue especially if the amp’s been “DIY biased” and you’re using power tubes within Mesa specs..

I’ve had couple of Mesas with adjustable bias and always converted those to original. Easier to just buy tubes within specs and drop new ones in… lazy

 

[user 41014]

The 1st thing I would do (or have a tech do if I wasn't doing it) is check the coupling cap that feeds those 2 tubes at the PI. There is one coupling cap for each pair of power tubes.

Dollars to donuts that's it. Change them both- at least 600V (.1uF)
https://store.mesaboogie.com/products/capacitor-film-met-poly-1uf-630vdc.html

 

[tbonesullivan]

Yep.. better to drop it off to a tech - who is no Mesa hater
red plating is usually sign of a bigger issue especially if the amp’s been “DIY biased” and you’re using power tubes within Mesa specs..

I’ve had couple of Mesas with adjustable bias and always converted those to original. Easier to just buy tubes within specs and drop new ones in… lazy

Yeah... way too many "techs" on youtube who had anything that has PCBs. They would probably run away screaming if they ever had to fix a studio mixer or any other real "sound repair" job, with fun surface mounted components.

I also am lazy, and honestly Mesa amp designs are really preamp heavy, so I don't really see a point of cooking the power tubes to get a "better" sound. I would rather have tubes drop in and work.