A good friend has an RD50 112 I worked on, recapped and modded the Distortion circuit. He never uses the Bright switch and would use it instead to get more bass, similar to what the Deep Switch does on the 65 series amps. Researched this site, didn't find anything really applicable. I have experimented by shorting the cap the Bright switch goes to, can't tell if it actually allows more low frequencies through or just makes everything louder.
Alternatively, if I could increase the low frequency range of the Bass control, that would work too.
Any suggestions welcome.