That's an interesting story and history about the clocks. I happen to
have the original type digital one, used in a 5065A. I don't have an
actual 5065A, but many years ago acquired a carcass of one - it was
missing the Rb physics and a few other things, but was a nice box for
re-use.
I eventually used it to repackage and improve a Z3801A GPSDO acquired
later. It turned out to be a good size and layout for this purpose. I
managed to squeeze in the rearranged Z3801A guts, an extra layer of
mu-metal shielding and thermal insulation on the OCXO, and a couple of
12V, 12 A-hr SLA batteries for backup. I used mostly the original power
supply, and put additional supplies and control circuitry inside the
original digital synthesizer box for shielding. The whole front panel
and clock were intact, and I wanted to re-use all that stuff, except
with different functions and labels - I especially like the door in the
center with controls and monitoring functions behind it.
The clock appeared to be a very complicated mess at first, and a helluva
thing to figure out without schematics. I eventually found the
schematics, and the data sheet for the PMOS clock IC, then everything
started to make sense.
It used a buck converter to make the low voltage for the LED display,
which I eliminated since I was making new, cleaner low voltage anyway.
The board also had some simple 1 PPS interface circuitry etc, that I
moved elsewhere, so two boards were left for the clock function - one
for the counting and control, and one for the LEDs. This made the whole
assembly much shallower, and I found that a tin can (6-1/2 oz tuna can,
as I recall) made an excellent shield/cover for it. I punched a bunch of
ventilation holes in it, mechanically mounted it behind the clock
assembly, and ran all the power and signals through feed-through
capacitors.
I also changed the internal LED supply to a variable shunt regulator, to
eliminate pattern-dependent load current. To the outside world, it looks
like a constant-current load, depending on the selected LED brightness,
regardless of the readout value. Finally, I fixed the "6" and "9" tails
on the LED readout. The appearance of the top and bottom segments on
these numbers depend on the particular IC used, and this one didn't have
them. This always bugs me, and I try to make it "proper" according to
me, if possible. It turned out to be very easy to add the tails.
Ed
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