I'm trying to figure out if a crystal microphone that was provided with a wire recorder is any good after some 60+ years, though I have yet to complete my restoration of the recorder itself, I have been trying to test the mic. At this point, I am thinking that it is dead based on simply plugging it into several tape players, computers, etc, I am not sure if crystal microphones take siginificantly more voltage to read properly, or if it actually is DOA. Anyone here have much experience with these old tin cans?