Mark III weak overdrive

[The Rude]

Hi. I have a Mark III with very little overdrive, it's like a limiter is kicking in somehow. The clean channel sounds fantastic, but the drive is not good. I have tried different speakers and tubes, but it still the same. I know this is a difficult question, but any tips?

 

[nor]

Which tubes have you swapped out? From the manual...

...V1, as we said, is usually the culprit for general noise problem , especially when both Rhythm and Lead Modes are affected, or if the amp is dead. V2 can also be the culprit for dead amps. If you plug your guitar into the Effects Return Jack and it produces sound - which it should - then chances are your power tubes and output driver (V5) are OK and V1 or V2 is at fault. V3 contains the Lead Mode circuitry so if the problem seems limited to the Lead, Change V3. (High settings of the Lead knobs also require a good quality V1.) V4 is the Reverb tube. Change it if you have a reverb problem. But first check that the reverb cables are plugged in securely. Grey cable goes in the socket toward the front of the amp. V5 is the socket which is set back mid-way to the output tubes. It can be the culprit if the amp is dead, has low gain or lacks boldness, warmth and/or clarity.If you are in doubt, you should merely replace the preamp tubes one-at-a-time beginning with V1. If the replacement tube fails to cure the problem, put the original tube back into its socket and go on to the next.

I just had a similar issue with substantial gain reduction. Dirty EQ sliders were the culprit. Dirty potentiometers could also cause the issue you have described. Marks are dust-bunny magnets, need to be cleaned regularly.

If you are not experienced working inside a tube amp - DON'T. The capacitors in the old Marks store a TON of energy - enough to end you.

A tech may be necessary if it is really dirty. But sometimes you can work the dust free by exorcising the knobs and sliders. With the amp OFF turn each knob to 10 to 0 to 10, etc. Same for the EQ sliders and any knobs on the back. Once everything feels consistant, power up and VERY CAREFULLY do it again. Be mindful of your Master settings, lol. Listen for crackling or buzzes as you repeat the process. Same process with the jacks. Plug-unplug-plug-unplug, etc.

Hope this helps!