WS19 Headphones - how to make operational

[Patrick Johnson]

Hello,
I'm hoping someone on MLU will be able to suggest ways to reactivate a number of WWII 19 set headphones in my collection. I have a three sets (of 4 total) that I can't seem to get to work. At the moment my only test is when I press the "Call Commander" button on the Driver's Control Unit, the buzzer is clearly audible in the earcups of the operational set. The same test doesn't produce results in the others. Is there a way to kickstart these, just in case the speakers need a little prodding to reactivate?
Additionally, would or could these be tested with modern stereo equipment, or are they simply too primitive or of the wrong impedance to reproduce sound?
I am in the process of setting up the complete wiring system in a Sherman tank, complete with the three Control Units, and ideally would like to get at least two headphones working so that two "Crewmembers" could communicate with each other. The wiring is up and running and appears to be working fine, the lights come on and the buzzer works, I simply need two working headsets to take the investigation one step further.
Thanks for any assistance or advice you can offer.
Regards, Patrick