F50 Clean Channel Breaking Up Early?

[BonesMachine]

I just picked up this amp and have been playing it for a few days with a PRS guitar. I read that these amps have a nice clean channel for loud and clean. This amp seems to be breaking up pretty early? The clean channel is kind of raspy with master at max and gain at 9 o'clock. There is some pretty heavy break up with the gain at 12 o'clock and all out over the top distortion with gain at max. Does this sound about right for this amp? The break up sounds pretty good (a little raspy) but I was expecting way more headroom on the clean channel. Like Fender Bassman clean headroom? Should I be getting this much break up or maybe something is wrong? I tried swapping the Groove Tubes it had with brand new matching JJ's same break up. Tried a couple different speaker cabinets too. I tried out another F50 before this one that definitely had a problem with breaking up early so i don't know...

 

[user 84978]

Did you ever find out what was going on with your amp? I just bought a Rectoverb 50 Series 2 and I'm experiencing the same thing - lack of clean headroom. Also, when playing on the louder side in channel 2/Modern the OD doesn't sound right (but sounds good a low volume). Granted this is the first Mesa I've owned so I don't have anything to compare it to, but I would have to believe that I should have more headroom than this in a 50w amp. Also, others online talk about how good the clean channel is which leads me to believe mine is not normal.

Having said this, it seems to me like a screen resistor failed and all the load is going to one tube. I need to get the amp down to my workbench and open it up, but I wanted to see if you got yours fixed?

 

[user 84978]

Today I opened up my Rectoverb to do the parallel to serial effects loop mod, and sure enough one of the screen resistors was only connected on one side of the board - the other side was hanging down. I checked the values of both and they are in spec, so I removed them and soldered them to the top of the board. Night and day difference with this amp. I now have a so much more clean headroom and the Modern channel sounds what I expected a Mesa to sound like.

Hope fully this helps someone else experiencing a similar problem.

Before. You can see the bottom resistor is slightly underneath the top one. Also, it was melting the shield of the wire it's hitting.

After. I confirmed the gray wire was not melted through

 

[pulteney]

I just picked up this amp and have been playing it for a few days with a PRS guitar. I read that these amps have a nice clean channel for loud and clean. This amp seems to be breaking up pretty early? The clean channel is kind of raspy with master at max and gain at 9 o'clock. There is some pretty heavy break up with the gain at 12 o'clock and all out over the top distortion with gain at max. Does this sound about right for this amp? The break up sounds pretty good (a little raspy) but I was expecting way more headroom on the clean channel. Like Fender Bassman clean headroom? Should I be getting this much break up or maybe something is wrong? I tried swapping the Groove Tubes it had with brand new matching JJ's same break up. Tried a couple different speaker cabinets too. I tried out another F50 before this one that definitely had a problem with breaking up early so i don't know...

Sorry, just read this. I’ve owned and played an F-50 for maybe 15 years. With stock preamp tubes, the clean channel stays very clean up to +/- 3 o’clock. No raspiness with gain at 9 o’clock.

By the way, master at max you said?! I’m impressed; the F-50 is L O U D.

 

[user 84978]

Today I opened up my Rectoverb to do the parallel to serial effects loop mod, and sure enough one of the screen resistors was only connected on one side of the board - the other side was hanging down. I checked the values of both and they are in spec, so I removed them and soldered them to the top of the board. Night and day difference with this amp. I now have a so much more clean headroom and the Modern channel sounds what I expected a Mesa to sound like.

Hope fully this helps someone else experiencing a similar problem.

Before. You can see the bottom resistor is slightly underneath the top one. Also, it was melting the shield of the wire it's hitting.
View attachment 2089

After. I confirmed the gray wire was not melted through
View attachment 2090

**UPDATE** After posting this in another forum I'm on I was told by a tech that works on Mesa's that the screen resistors being mounted under the board is by design. If/when a tube fails instead of taking out more components, the solder at the screen resistor heats up and it drops from one end. Which is what appears to have happened here. I have since relocated the resistors back under the board.