[Milsurplus] TBX Modulation

[Robert Flory]

Hi,
I'm flying without a manual, here, and beating my head against the wall to
get more than about 50 percent modulation out of TBX-4 and TBX-6 units.  
It seems that theory ought to allow for 80 or 90 percent, but since both
run about the same, I'm wondering if the low modulation is normal.

Operating conditions:
Self-Excited Mode
Ep=500V
Eg2=200V
Eg1= -75/80V
Eg3= -30V

The modulator drives the suppressor g3 well into positive range which
suggests that modulation audio is wasted.  RCA 837 spec sheet wants a
larger bias on a suppressor modulated amp, like -65V.  When I look at the
voltage divider that derives the suppressor bias from the grid bias, there
is no way to significantly increase the magnitude of the bias by moving the
tap.

Any thoughts?

Rob Flory
www.home.earthlink.net/~navyradio