[ctvpa]

I also collect telephones. (a hobbie that, sorry to say, is evaporating)

Do you think this is working just by conduction? I see no transmitter, or any way to generate any current to the receiver. I have used a stethescope often, and I find that if I take the diaphram off the stethescope and place a metal rod, and touch the rod to the engine I get great results via the earpiece. A friend has a tin can that he bolted a 2 foot wire onto the bottom, he places the wire on the motor, and the soup can over his ear, it works great.

I am interested in your photo, but do you think you are getting sound via the electrical receiver (while you have no electrical connection). I might try to disconnect one of the receiver wires and see if what you are really hearing is conduction rather than transmission of sound. Either way, it looks cool.

I also agree the long screwdriver to the ear works great, and it is always my first choice. I have the stethescope because I am in the medical field and have a few old ones that I 're-purpose'.

JMHO (Just My Humble Opinion)