[Amps] Grid Bias Supply followup

[TexasRF at aol.com]

Perhaps the -100vdc is used for cutoff bias in receive?
 
A typical t/r circuit might use a set of relay contacts to lift the + end  of 
the rheostat from ground on receive thus allowing the full -100vdc to appear  
on the center of the rheostat and tube grid(s).
 
73,
Gerald K5GW
 
 
 
In a message dated 3/22/2008 6:26:27 A.M. Central Daylight Time,  
kk7uv at bresnan.net writes:

As a  followup to my question about the grid bias supply on the G.E. Ham News 
813  amp (and the B&W LPA-1 is nearly the same design):  

The bias  supplies for these amps use a 120:120 transformer, half-wave diode 
rectifier,  C/RC filter (40uF/500 ohms/40uF) and a 500-ohm, 25-w rheostat load 
for the  adjustable bias.  These supplies are said to provide zereo to -100v  
bias.  Yet, the settings for CW and SSB only use -19 volts and -5  volts.  
Why then, is it necessary to have -100 volts available?   Seems like a much 
smaller supply would suffice.

Thanks, Steve  KK7UV
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