Headset question for avionics engineers
 

I have acquired a small collection of Racal Astrolite pilot's headsets over the last few years. One has an amplified electret microphone, the others have amplified electro-magnetic mics. Does anybody know if these have an optimum or minimum voltage to permit operation ? Would they be compatible with modern cockpits among the likes of Bose, David Clarke and so on ? At least one of the headsets is an ex-British Airways unit and a similar one has never been used at all.

I have no means of testing the mic circuits but I would be interested to know if there is a likelihood of any of these headsets being useful and working.

Thankyou.