Hi, Julio. The relay in the SB-220 is 110 VDC, a number that is too high for the solid-state switching in many modern transceivers. However, I used an unmodified SB-220 with a TS-930 for several year
I don't think it's the capacitor that's at fault, but the lack of a "catch" across the relay. In any case, the easy way to add the reistor is in the cable, which puts the resistor outside the amp alt