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Carbon microphone revitalization
I do not. BUT, I would suggest first of all measuring the static resistance
of the microphone and comparing that with the resistance of a known-good microphone. The static resistance is about 100 ohm, but I do not have another carbon microphone for comparison I might also try using a telephone transmitter element (in the US we have lots of Western Electric T-1 transmitters everywhere) and comparing that with the test microphone in measured sensitivity. --scott I tried to power the microphone with 12 V through a 1200 ohm resistor. Talking loud into the microphone and with the mouth very close to it, the scope (put across the microphone leads) shows a peak voltage of about 600mV (or 1200mV p-to-p). Perhaps it is good enough, but I am not sure on whether the bias current is too low, and I should then try again using a lower resistance. 73 Tony I0JX |
#2
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Carbon microphone revitalization
"Antonio Vernucci" wrote in message . .. I do not. BUT, I would suggest first of all measuring the static resistance of the microphone and comparing that with the resistance of a known-good microphone. The static resistance is about 100 ohm, but I do not have another carbon microphone for comparison I might also try using a telephone transmitter element (in the US we have lots of Western Electric T-1 transmitters everywhere) and comparing that with the test microphone in measured sensitivity. --scott I tried to power the microphone with 12 V through a 1200 ohm resistor. Talking loud into the microphone and with the mouth very close to it, the scope (put across the microphone leads) shows a peak voltage of about 600mV (or 1200mV p-to-p). Perhaps it is good enough, but I am not sure on whether the bias current is too low, and I should then try again using a lower resistance. 73 Tony I0JX Microphones vary but 100 Ohms is about right. Take the audio from the series resistor rather than the microphone. Set the voltage so that the drop across the mic terminals is about one to two volts. You can run more but the least is the best. Most devices, transmitters, etc., using carbon mics use an imput transformer with a primary of somewhere around 100 ohms and a secondary suitable for what you are feeding, usually a high impedance. The exciting voltage for the mic goes through the primary usually with a capacitor across the battery to insure a low impedance audio frequency path and minimum noise. See what you get and post again. -- -- Richard Knoppow Los Angeles WB6KBL |
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