Since there is no manual available for this device, radio collector Tom Brent provides an educated guess as to the purpose of this device. "The term common oscillator leads me to believe it may have been the frequency control for receivers set up to operate in space diversity mode. Dual or triple diversity receivers were commonly used in point-to-point communication circuits.

Note that that common oscillator has the same frequency coverage as the upper 4 bands of  the CSR-5 receiver. There are 3 output connectors on the rear panel and, assuming they are original, would lead me to believe it was feeding multiple receivers. I do not know of any application where multiple transmitters at a station would be operated on the same frequency".


Model: 105-930.
Patented: 1927-44.
Serial no: 103.
Ranges: (MHz)  1.5 to 3.5; 3.5 to 7.5; 7 to 16 and  15 to 30 MHz
Logging Scale : 1 to 23
Rating: 250 VDC - 115 MA, 12.6 VAC- 1.3 A.
Physical: 19" by 13 1/2" by 8 3/4"
Weight: 35 lbs.
Circa: Believed to be 1944. Possible source of spare parts.

The example in the photo appears to have many parts stripped out so it cannot be viewed as an actual example of the Common Oscillator. (All photos via E-bay)
This dial assembly has been exrtracted from a Common Oscillator. ( Photo by John VE2VX) 

Contributors and Credits:

1) Tom Brent <tgb(at)>

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April 24/08