6V6s Ok in a 112 RD50

Will this work to get a lower volume or a bad idea?

Not a good idea! This tube is usually used in an amplifier with no more than about 450 Vdc on the plates.
You plug these into a Music Man with more than 700Vdc plate voltage and you will arc-over, blow tubes, pop a fuse and perhaps put your amp in jeopardy!
You need to use the original 6L6 tubes to have any chance of tube survival in your Music Man amp.
Steve

I also have an RD50. These amps are different than the other MM amps. They do not have 700 volts on the plates; however, they do have about 450-500 volts, as I recall, which is atill a lot for 6V6 tubes. Also, since these amps have fixed bias, this would further complicate the issue of swapping tubes. So, I agree, stay with the 6L6. Just my $.02.

Yes, the RD50 amps "only" have a 585Vdc plate voltage! This is still way too high for safely using a 6V6!
Steve