Please Help Identify a Mystery Device!

[RCHRDM]

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 on the front panel is "691."  It has tubes and what looks like 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?  Maybe a signal generator?

It has no chassis-mounted inputs or outputs but one of the coax cables on the back is longer than the rest and perhaps connected to another piece of equipment.

I have attached front and back pictures.  The space on the lower left on the back view had five band pass filters of various cutoff frequencies.

Richard

[Simon]

Please don't double post.