Resistor cutoff is the preferred method, since if you lose a bias supply you have sky high ZSAC when the amp is keyed or not. With the resistor cut-off method, you get the tube cutoff, you don't have 100 or so volts across the contacts of the relay (like the SB220, etc), etc.
I'd be careful with some of the 'info' in this thread. Nothing would kill you so far, but a lot of 11 meter 'voodoo' being repeated here.
1N5408s are crap for bias. They have a large excursion from 0 volts to their zener voltage (app .65) in current.... MEANING they will NOT hold your zener voltage constant..... MEANING, your bias will fluctuate like using a voltage tap resistor circuit.
6A10s are MUCH more suitable for creating bias blocks. And if the amp is going to be used on AM for any appreciable amount of time, try throwing in about 18 diodes. Even for 11 volts (stock), you'd need more than 11 diodes, 11 would give you about 7 volts of bias..., give or take depending on the diodes used.
BIG diodes, not necessary if the zener works. Strings of diodes are good for people that blew the zener, or those that know what they are doing, can monitor ZSAC and have a second receiver to monitor IMD with, and understand classes of operation.
Better thought might be to keep the zener in it.....
You've put a LOT of work in an amp you could have done a C check on the tubes... Usually bad tubes will have bent a element inside, and the C in, Cinternal and Cout won't be within tolerance... USUALLY. A high pot tester would have been good, too.
Might run into tuning problems with all the extra C you've put into the tank circuit..... That's almost 2.5 times the original amount of Cblock... You've got to be able to tune that additional C out somewhere, so either the tank circuit needs to be realigned, or you will have LOTSA Q in it, meaning sky high voltages and currents (bandswitches going out to lunch are common)...
Just my dollar eighty five worth.
--Toll_Free
