This military transmitter started out as a plate
modulated 100w ship to shore transmitter with a 4-400 in the final and a
built in modulator that included a pair of 807's. With the optional
SRT-15 package that included an external mounted modulator and a high
voltage power supply this became a 500 watt transmitter.
What I did was to remove the internal oscillator for the space
needed and designed the transmitter to be self contained with a HI-FI
modulator that uses a pair of 813's in class AB1.
speech amp uses (2) 6SJ7's with dual ladder feed back network and a
balanced 600 ohm audio input. This ties in directly into the grids of the
813's which of course uses a mod reactor and the door that covers the
modulator tube was the access door used to change frequency under the old set
up. With all the wiring changes this project took longer than building a
transmitter from scratch.