Question about the RAF microphone used with the TR9D - UK Vintage Radio Repair and Restoration Discussion Forum

Gridiron · 27th Jan 2019, 10:54 am

On looking at the circuit of the TR9D transceiver used by RAF fighter planes of the Battle of Britain period, the microphone type 18 is connected in series with the transformer primary across the 2 volt filament supply to the valves as a carbon mic would have been. It is called an electromagnetic microphone and I was wondering if the current which must have been drawn was to energise the mic as in a field energised speaker or to help increase the magnetic field if a permanent magnet was used.
Later microphones of this type as used with the A1134 amp, for instance, are not used with any DC supply. Incidentally, I noticed in the 60's film of the Battle of Britain later mics are used by the pilots, the type 18 is now very rare and replicas are made for collectors of period flying clothing.
Mike.

27th Jan 2019, 10:54 am	#1
Gridiron Heptode Join Date: Apr 2010 Location: West Midlands, UK. Posts: 662	Question about the RAF microphone used with the TR9D On looking at the circuit of the TR9D transceiver used by RAF fighter planes of the Battle of Britain period, the microphone type 18 is connected in series with the transformer primary across the 2 volt filament supply to the valves as a carbon mic would have been. It is called an electromagnetic microphone and I was wondering if the current which must have been drawn was to energise the mic as in a field energised speaker or to help increase the magnetic field if a permanent magnet was used. Later microphones of this type as used with the A1134 amp, for instance, are not used with any DC supply. Incidentally, I noticed in the 60's film of the Battle of Britain later mics are used by the pilots, the type 18 is now very rare and replicas are made for collectors of period flying clothing. Mike.