The Hp 8640B is a superior instrument to the Wavetek 3000/3001 etc,
but as someone pointed out, caveat is that the 8640B is painful to
repair. It has a tunable cavity for the RF generator, explaining the
spectral purity. The prices of these things have dropped over the
years, used ones were about $1500 in the mid 1990s, and now they can
be had for $300 if you are lucky.
Things to watch out for are noisy output attenuator (or burnt ranges)
and a bad pot for the variable attenuator. This assembly can be
removed as a unit, if you get underneath the unit. Depending on which
model, sometimes the oscillator stops (on mine) at the ends of the
freq bands, but it always restarts if I just move around the crank
and come back.
I have the militarized black face version in the heavy yellow box.
They are very easy to find since DOD has quit using them. It lacks
the frequency lock feature that locks the osc to the counter
timebase. It does have the freq counter, though, as if i leave it on
for a long time, it is damn stable. The 8640A had a slide rule dial
and lacked the counter altogether. Avoid that one.
Later, HP developed the synthesized 8642A and B, which had similar
performance to the 8640 in most respects, but was much more complex
and used microprocessors. It is a very heavy and deep unit, and last
time I checked, was still supported, due to the DOD users. It has
built in fault diagnostics and self test features.
73
John
K5PRO
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