In May 1931 RCA demonstrated their ribbon mic in Hollywood and it came to the BBC's notice. Unfortunately the price, including the head amplifier, was £130 which in today's terms is around £5200. As this was not affordable, the BBC set about designing its own version, which was introduced in 1934-1935 as the Type A microphone. There was some concern about the possibility of patent infringement but eventually it was decided that the BBC had a valid patent. The mic was manufactured for the BBC by Marconi for £9 each, about £360 today.
The original aluminium ribbon had objectionable resonances and was replaced with very thin aluminium foil and the modified mic was called Type AX. Another problem was found when the mic was used near an electromagnetic field; this was solved by arranging the internal wiring of the mic so that induced noise currents cancelled out and thus the Type AXB was born in 1943.
The final modification was to use Ticonal magnets in place of the original cobalt steel magnets. This gave 6dB increased sensitivity and the letter T was added to the code number. Weighing in at just under 9¼ lbs., type AXBT appeared circa 1944, and is illustrated here.
Chris's collection also includes the empty case of an original Type A mic. He understands that it was once owned by a BBC photographer who used it as a prop in many pictures. Has anyone got a yoke and spigot or the 'works' of a Type A to allow this mic to be restored to working order?......
