Express 5 25 1X10 bad overdrive

[Brian Blondahl]

I'm noticing that all settings except clean suddenly have too much overdrive. On crunch I cant get past 12 noon before the distortion is overwhelming. Not as bad on Blues but very bad on Burn. I'm in the process of swapping out preamp tubes one by one. Power tubes are new and the amp plays clean when I plug in the return jack of the effects loop so the power section is OK. Anyone else have the same problem? Hoping for an easy fix but not expecting miracles.

 

[Don]

You haven't unplugged and plugged the reverb cables back in, have you? Swapping the cables can increase the gain pretty dramatically.

 

[DrKev]

All settings *except* clean, which suggests a preamp issue. That means tubes V2 (which is the input tube on these amps) or V1 (which comes after the tone stack but before the master volume), or something else. Looking at the schematic (non-expert disclaimer) I there is only a small section that is common to crunch, blues and burn, and V2B is in that path.

How did the tube swapping go, Brian?

Did you try emailing Mesa?

 

[Brian Blondahl]

All settings *except* clean, which suggests a preamp issue. That means tubes V2 (which is the input tube on these amps) or V1 (which comes after the tone stack but before the master volume), or something else. Looking at the schematic (non-expert disclaimer) I there is only a small section that is common to crunch, blues and burn, and V2B is in that path.

How did the tube swapping go, Brian?

Did you try emailing Mesa?

Thanks for the replies. Problem solved. V2 tube was weak and V1 and V2 preamp tubes were not grounding properly. cleaned up the pins and the tube covers.

 

[Brian Blondahl]

Thanks for the replies. Problem solved. V2 tube was weak and V1 and V2 preamp tubes were not grounding properly. cleaned up the pins and the tube covers.

 

[edward]

^^^Good to hear! I love my 525, ver1 ...what a great sounding and tonally versatile little amp! As you already found, that V2 is a critical tube. And though you've fixed your issue, this is also a good place to experiment with tube replacement.

Not the entire preamp tube section, but just the V2. You can try different 12ax7s, and also a 5751 which is a slightly lower-gain 12ax7 and this will "gain down" the entire amp so all channels will change in character; nice if you're more into a low-gain or mild break up tones. Food for thought, anyway

Edward