75786 Spark Gap Transmitter


Type: Quenched gap, spark transmitter.
Frequency Range:  600 to 730 metres. (500 KHz to 410 KHz)
Power: 50 watts
Dimensions: 16.25" W x 15.375" D x 21 "H
Circa: 1939
Comment: For emergency use only.


The equipment itself consists of a dynamotor and the transmitter. Supplying power, is a dynamotor with a 24 DC input and connected to the emergency storage battery. It delivers 100 volts at 600 Hz to power the transmitter.

75786 Transmitter Manual PDF (Courtesy Laval Desbiens via Spectralumni)
A side note on spark gap transmitters. In simple designs,  the spark was created between two brass balls whose distance could be adjusted for best results. After some use, the balls would become dirty resulting in harsh, rasping transmissions. After cleaning, the signal sounded quite pure and pleasant to listen to. When the balls got dirty, the signal became very hard to copy  one often heard one operator tell another to "clean your balls".

Contributors and Credits:

1) Spectralumni  http://www.spectralumni.ca/
2) Laval Desbiens <desbiens.laval(at)videotron.ca>

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May 20/10