[Hammarlund] HQ-129x - Xtal Calibrator Puzzlement

[Barry H]

Just got another HQ-129X.  I think this is my third or fourth -- lost count.

Amazingly it arrived in working condition -- defying the crummy packing job.  Fortunately a short trip and no apparent bounces.

This one's all original except for two things.  Someone replaced the original somewhat anemic tuning knobs with somewhat less impressive TV push-ons.  Not a purist, but I'll be looking for somewhat better replacements.

Here's the puzzle.  A previous owner added one of those small aftermarket crystal calibrators -- very neat job in the left rear corner.  It uses a 6AU6 and a 100 kHz xtal.  The tube is lit.

I can't find a switch anywhere, and all the original switches seem to operate as expected.  (Thought maybe the send-receive was re-wired to turn on the calibrator or limiter or something -- not apparently so.)

Anyone have any ideas?  Yeah, I know, I could pull the chassis and take a peek -- trace the wiring -- but that would be cheating.

Also checked for any pots that might have been replaced with one with a built-in push-pull switch.  Nope.

Standing by.
Barry