TMC Passive Voice Control unit

[Opcom]

Came across this TMC manual - Model PVC-1 / PVC-2. It uses a bucking winding in a dual transformer setup with apparently standard audio transformers, and a thermistor for a level detection and control element which acts upon the incoming audio power. The thermistor is not well identified, I am guessing that the less massive it is, the faster the unit reacts.

The manual is attached. It seems pretty interesting and very simple.