Music Man Amps

Holy crap Batman- a 2-10 130 with jbls! THAT MOFO is heavy! Those filter caps need to be replaced pronto. I would suggest replacing ALL the elctrolytics in the amp (the silver tubular ones), and make SURE you replace the ones on the bias supply board. That amp has the SS driver so it's a little more stable than the tube driver versions but those look like the original 6CA7's from like 1978 so they could be a sore spot. Mike.

Nice find! Welcome to the forum.

If it sounds good, why not just play it and enjoy it? There is a big difference between a Music Man amp from the late 70's and a Fender amp from 1963 - it's not a given that you will get any difference in sound or stability by changing the caps at this point.
It would appear that your amp has been converted from the original 12AX7 phase splitter to the later transistor driver setup in 1980 (as noted inside your chassis). One telltale sign is that you have the 2 x 20uF capacitors in the metal can. The later amps lack these.
If the amp starts sounding muddy or noisy, or if you get hum from the speaker - then yes, it's time to put a set of Sprague Atoms in there and, as Mike '210' Kaus pointed out, replace a few key components. The 150k resistors on the rectifier board, all four 150uF filter capacitors in the low voltage section are good places to start. The zener diodes in the +/- 16V supply may also be replaced - but then again, your amp is a slightly later one and was gone over in 1980 at Music Man (one would assume). Anyway - as I stated before, if it sounds great - well, then - great! Take a polishing cloth to it, get a cover for it (if not already equipped) and enjoy. Those JBL speakers look interesting for sure. One can only speculate if they were a special order item or were added later. If you look at the speakers for date codes, that could solve that mystery.

Cheers,
Lars Verholt

Depends on how much they were used. I've got original 6CA7's here that are new with only a few hours on them so THEY are in great shape. I will say that those tubes will last a hell of a lot longer than any new production tubes. If it sounds good, play it. I sure wouldn't replace them just because they are old (so am I) Mike.

In case you haven't read it yet, you might go to to the maintenance section and read the bias setting procedure for the SS driver amps and check it. Its pretty simple and you can at least check the drive section to see if it's running hot or not. Mike.

http://www.pacair.com/mmamps3/sites/default/files/docs/MM%20Service%20Bu...

You won't need the tester for this procedure. You are measuring the voltage on fixed resistors on the driver board. Mike.

Those are very balanced readings. I've seen them WAY apart and still be great. I had one (my own at the time) that the driver transistors were WAY apart and it distorted to beat the band. If your are that close, y'all is in great shape. Mike.