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Dear MMDers:  Some time in the 1920s my late father, who was earning
his living building high quality radio receivers, modified one of
these monsters to enable messages to be spoken to aircraft pilots at
Woolsington (now Newcastle) Airport.

He drove the comb by attaching to it the vital bits of a reed headphone.
Thus the microphone provided a signal to a modest valve amplifier,
whose output vibrated the comb.  I was not yet born at the time, but my
father told me that the device certainly transmitted speech well enough.

Ted Bowman, Clophill, U.K.