I bought a nice, old rack mount cabinet at an electronics swap meet last year. Inside it was a mystery box made by Sierra Electronics. (I made the purchase for the cabinet, not what was in it.)
The only number stamped on the name plate was "691." It is has tubes and what look like some kind of tuned circuits with a separate circuit for 2, 4, 10, 20 and 30 MC (MHz).
Does anyone have an idea of what this device is? I have attached a picture.
Richard