[mikethedruid]

Actually, if you look at the data sheet I posted for the 71A, the bias required for maximum efficiency as an audio amp varies with the positive plate voltage applied. If the plate voltage is +90 volts, the grid bias should be - 16.5 volts. If the plate voltage is +135 volts, the grid bias should be -17 volts. Only when the applied plate voltage is the maximum recommended, +180 volts, should the grid voltage be -40.5 volts. I am not sure what the applied plate voltage is in this application.