Is it really necessary to have operating bias on 811A's ? If so, is 4.5 to 5 volts a good value ? Can a string of 2 to 3 amp rectifier diodes be used instead of a Zener ? I am currently using a 47 ohm resistor from grid to ground on each tube (4) and am not sure this the right way to go about it. Any ideas and/or comments. Thanks....73 Ed W3NR