Hi!
This thread is very interesting... and timely for me. I am putting together a modified Heising modulation "adapter" for my Ranger. It will plug into the 9-pin socket on the back of the Ranger.
I downloaded the reference text on Heising modulation that Ian provided a pointer to:
http://www.pmillett.com/Books/Lee_1955_Electronic_Transformers_and_Circuits.pdf... and printed out Chapter 6 section 80 (pp. 192-198). I think it makes good reading!
I am planning on using a 20H choke in my Ranger modulation adapter... which means that the impedance of the choke equals the plate resistance of the 6146 (~600 volts / 120 ma = 5000 ohms) at a frequency of approximately 40 Hz.
I am going to start with 2.5 uF of capacitance (four 10 uF 450 volt capacitors in series, with a 100 kohm "equalizing" resistor across each capacitor)... which is about 5x too large for achieving the desired resonant effect that is described in the reference text. I plan to try 0.5 uF as well.
It will be interesting to see how the modulation performance (both measured frequency response, and on-air reports) changes when I switch back and forth between the standard (non-Heising) configuration and the modified Heising configuration... and also when I switch between the 2.5 uF capacitor and a 0.5 uF capacitor.
I'll report back in a few weeks (I'm waiting for the back-ordered choke... which, hopefully will arrive by then).
Best regards
Stu
