kh wrote:

Speaking of Gaithersburg, if you google for "R-9xx Collins", you'll
get a page that discusses the fabled R-390A that had a factory built
LED digital display in place of the Veeder-Root mechanical counter.

About 30 years ago I saw one of these for sale at Gaithersburg. It
wasn't a homebrew job, the vendor had the manual for it, I recall
that he fanned it and showed folks the circuit diagrams. That's
diagrams, plural.

So you Collins types, a piece of trivia, the "R-9xx" is real. I was
"this close" to it. I wonder where it is today. I bet that an
R-9xx would make an SX-88 or KW-1 look cheap.

One of the ways I make a living is designing prototype equipment for
the US Army. I have in the past modified items that were in the usual
military supply stream to add features that were desired by my customer.

The unit you saw could very well be a modification that was done by some
nameless vendor, like myself. Collins, or any of the other R390 manufacturers
likely had nothing to do with it.

-Chuck