Jr.,
The 190B is basically a re-branded 200S. As I recall Sunn started making the 190B around 1974 (I have one with the matching 215S speaker cab.). You would need to compare schematics with the 200S, but I think they were nearly identical......a pair of 6550's putting out about 60 watts RMS. The polarity switch reverses the hot and neutral AC leads. This prevents nasty shocks (sometimes lethal) when you touch another piece of live equipment (amp, mic, guitar) while simultaneously touching your amp or instrument. Your amp will also produce less background hum in one position than the other.
Good Luck!
Ryan
