VMX, VMA question

Has anyone looked inside a Brauner VMX or VMA microphone or  power supply to check what is changed  from a VM1?

Some guesses

Uses a relay to switch inside the microphone

SP relay changes cathode resistor value adding in parallel.

DP relay changes cathode resistor value adding in parallel and/or changes the tube plate voltage by adding a resistance in series "above" the plate resistor.

The VMA PS mounted switch could also adjust B+ voltage and heater voltage supplied to the microphone.

I am curious what is being done.