[Amps] Alpha 77Dx Filament Mod (Epilougue)

[Paul Christensen]

Just received my new 8877 and thought I would share with the group the final 
outcome of my results.

Recall in prior postings that my intent for the Alpha 77Dx modification was 
to: (1) un-ground the filament and utilize a dedicated return line for the 
8877's filament; and (2) lower the filament voltage from 5.75VDC to just 
under 5.0 VDC as the specified range of operation from Eimac is 4.75 VDC to 
5.5 VDC.

After installing the new filament RFC, 0.1-ohm wirewound series resistor, 
and new 8877, I measured the filament voltage at the tube's pins and 
observed just over 4.2 VDC.  In fact, the voltage drop through the new RF 
Parts choke is just enough to drop the voltage at the pins to just under 5.0 
VDC.  So, I completely eliminated the new series resistor.

At least for now, the amp operates great with no anomalies and the filament 
is completely isolated from the chassis.  The filament is not tied to the 
cathode at the moment.  The addition of one new jumper is all that's needed 
in case I desire to tie those two elements together.

Paul, W9AC