Now don't get me wrong, I think $16,000 signal generators are worthy
of respect. The 8640B, not so much. I had the bright idea of buying
a few of these in as-is condition and fixing them up, reselling them
for many $. Profit !! Woo Hoo.!!

here's how it's gone so far;

These things are heavy. There seems to be some unbreakable rule, if
you want to generate signals down to -130dbm, you need fifty pounds of
thick aluminum castings to contain all the stray waves. The weight
means you're $50 in the hole right away just for shipping.

They're wonderfully complex. What you'd do today with a fly-speck of
PLL synthesizer, HP did with a half-bazillion discrete parts. Even if
the parts only fail one every X hours, there's so many parts the
effective Mean Time To Failure is not much more than a day. The number
of gold-plated SMA connectors, switch contacts, pc board edges is
large. Each is a potential point of failure.

They're both sturdy and fragile, which is a bad combination. The case
is sturdy but the plastic knobs and nylon gears are crumbly. Most of
them arrive with broken bandswitch and FM deviation knobs. The power
transformer has its fragile nickel-tin pins soldered to the PC board.
Guess what breaks if the unit is set down a bit harshly? The slide
switches and some of the rotary switches are custom gold-plated jobs
that are unacceptably fragile and of course unobtainable.

They have unacceptable amounts of unobtanium. Luckily, not a bit of
software or EROMS in these. But a half-dozen gold-plated analog and
ECL IC's with the doomed HP 1820-xxxx part numbers on them. If the
ECL ones go, and they will go, the counter and phase-locking breaks.
If the jumbo TO-3 amplifiers go south, and they will, as the chips
were not glued down into the carrier properly,you're SOL, there's no
microwave 25dB amplifier chips in Jumbo TO3 that run off 44.6 volts!
The fan is only slightly less complex than a Pratt and Whitney R4360.
And the aforesaid gold-plated switches.

They're very hard to work on. Many modules are hidden under 30
screws. I've opened and closed the divider and filter boxes so often
the threads are wearing out. And the filter module still cuts out if
i tighten all the screws! Arggghhh!

The militarized -323 version is a teensy bit better-- at least the
knobs are sturdier.

So lesson learned::: even if HP got these to work well just
marvelously as they left the factory in 1975, they're kinda a DOG
these days.


FYI




So far I've been able to make two mostly working units out of five
basket cases.