Ed,
Checking the "BAMA' website returned the op manual and a couple of other things.... For the SX-42, the B+ on the schematic was 250 volts. what I would do is replace the caps with something higher than 250; 300 volts is a nice starter....The Cap values were 20 , 30 uF... I'd look for something like 33 uF, 350Vdc.... $$ 2 or 3 a piece....
Check out bama, its free...
http://ftp://bama.sbc.edu/downloads/hallicra/sx42-2/Halli_SX42_manualx.pdf klc