apparently there was an issue with the earlier tourmaster power plant power transformers. as far as i know, if you dont have an "m" before your serial number, it means the amp wasn't "stock" modded.
some of the older TMs were modded aftermarket to the tourmaster "version 2- "" M "" " mod, but won't show it on the serial number.
the mod involves a new power plant, and some different components replacing older ones on the circuit board to tighten up the gain and bass and take some of the harshness out of the treble.
i did half of the "M" tone mod. and am waiting on a new power transformer. hopefully soon! they got mine on tuesday, so, for what i understand, Nate is pretty expedient about getting new PT's out to people!
one thing i WILL recommend to you, if you own the combo, and if you have ANY ability to solder, open your chassis, follow the reverb driver wires from underneath (theres only 4 of them i think) onto the board where they just slide onto those spade clip type attachments..and solder them hard to the spade clips that they're attached to on board. one of the wires on my amp vibrated off and it took me FOREVER to figure out what was causing me to not have reverb, so when i found it, i soldered them all on. i may even solder all my PT wires on the spade clips too when i reinstall it.