[Chad Hauris]

12a tube yes is lower plate current, manual states 7.7 ma at zero signal.
filament is 5.0 volts at 250 ma current. Max plate voltage 180.
The GE tube manual is what I have here from 1973...it has all the common old 1920's tubes listed. Just about all tube manuals seem to have the vital specs on the old tubes...the older manuals likely have more detailed data on them.

As far as plate voltage, as long it is under the recommended maximum value for the tube (and negative bias is at least as much as recommended) I don't think it is terribly critical. Filament voltage, though, should be kept closely to the recommended value or very slightly less for good tube life.