[Milsurplus] GRC-9 modulation question

[Hue Miller]

I recall from about a decade back in ER, Walt Hutchins in an
article on the GRC-9 mentioned that it seemed impossible to
get a high modulation percentage, and the solution was to 
raise the negative bias on the 2E22 suppressor.  However in
reading TM 11-5820-453-35 dated 1971, i see there is a 
procedure to check modulation level via input audio voltage
for 100% modulation. So, 100% modulation appears not to
be impossible. So does a lessor modulation level imply poor
carbon microphone output, as often experienced?  Or????
What do others think about Hutchins's solution? FYI, the -35
manual specs not more than 0.5 volts audio into the microphone
input, via an audio generator, for 100% modulation, as the 
test spec.

Or- what about separating the HV B+ line and supplying 420
DC with modulation from an external modulator? Sinful?
-Hue Miller