[Amps] Alpha 77Dx Filament

[Paul Christensen]

Looking for opinions on the subject of 8877 filament voltage...

Due to high AC line voltage here (~ 127/254 VAC), my 8877 filament sees 
approximately 5.75 Vrms (as measured on a Fluke 189 True RMS DVM).   The 
8877 is rated by Eimac to run at 5.0v (+/- 0.25V).  Eimac specs filament 
current at 10A.

Since the filament current is significantly less than it would be on a 
directly-heated cathode, I am considering bringing the filament voltage down 
0.75V by using a series 0.075-ohm @ 20W wirewound resistor with integral 
chassis-mount heatsink on the secondary side .   The resistor would bring 
the filament down to 5.0V and dissipate about 7.5 watts of heat in the 
process.  However, if I can find a nearby mounting hole to add an angled 
aluminum mounting bracket, I could use a 0.1-ohm @ 25W rheostat.

I suppose yet another option involves series limiting the common HV/filament 
primary side to bring the line voltage back down to 235VAC or so.  Whatever 
I use, I need to make the mod reversible without hacking things up and 
affecting the re-sale value of the 77Dx amp.

Paul, W9AC