[OZ4]

On the bias voltage it's hard to tell exactly what you should measure. From the database on the 77   -2 volts doesn't sound out of line. With a plate voltage as low as 76 volts it maybe a little much. Your other voltages sound good so from the non linearity on the output either the tube is bad or one or more of the caps in the plate circuit are bad. Try swapping the 77 tubes and recheck all those caps and resistors in the plate circuit.