>Many thanks to all those who offered input in response to my query about
>the merits of adding the second tube to the Alpha 77S type amplifier.
>The thoughts were insightful and the general consensus was that the
>effort was worthwhile. In the planned project, I'll be using the
>Ameritron series amplifier as the base for the project.
The fly in the ointment is that the AL-1500 tank L gets mucho hot with
one 8877. With two tubes and 2x the I-anode, figure c. 4-times as much
_ A tetrode with handles is a practical solution for those who dream of
>Only one concern
>remains. On all the 8877 retrofits I've done, I always used a discrete
>filament transformer in the circuit. I was able to fire up the filaments
>and cooling fan and after the mandated 3 minute delay, I'd step start
>the plate transformer and away I went. In the current project, I'll be
>using the Peter Dahl replacement 77S transformer with the whole range of
>filament and accessory secondary windings off the single primary. The
>question is :
> a. is it permissable to apply high voltage simultaneously to the
>filaments and plate and wait the delay time before applying excitation?
>Eimac data sheet just mentions "cathode warm up time 180 seconds).
An Eimac engineer told me that a 3 and 1/2 minute warmup is mo' betta.
> b. does it make good sense to place a vacuum (or a good quality ) relay
>series installed in one leg of the high voltage AC secondary and let
>that switch in the HV to the rectifier board after the delay?
Not if cutoff bias is applied during heater warmup. This can be
accomplished by switching 100k-ohms in the cathode during standby.
>Thanks, Ron W2CQM/3
>Amps mailing list
Rich, AG6K, 805-386-3734, www.somis.org / new e-mail adr firstname.lastname@example.org