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[Amps] Dual 8877 Alpha 77S final query

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Subject: [Amps] Dual 8877 Alpha 77S final query
From: 2 at (2)
Date: Tue Jul 29 13:32:11 2003
>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 
tank loss.  
_   A tetrode with handles is a practical solution for those who dream of 
more steam,. 

>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, / new e-mail adr

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