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HP 8566B - What to look for?

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W4PJB:

--- Quote from: G0HZU on June 08, 2024, 11:59:28 pm ---
Is the high band range completely dead or is the displayed level just really low?

--- End quote ---

I only had a few minutes until the display quit, but from what I could tell, dead. I had a source going in at 0dbm, through a 30db pad, and 10db of attenuation in the 8566, and I got absolutely nothing on the graph. The low range peak was exactly where expected. As soon as the relay clicked into the 2-22 gHz range, I couldn't get a reading anywhere. I have a 6 gHz source and tried at 2.5, 3.0, 4.0, 5.0, 5.5, and 6 gHz, and nothing registered on the screen.

The high band noise floor looked like the one in this photo (not mine, it's from the web).

Thanks!

KE5FX:
Yeah, that's a low-hours unit.  The CRT HV lead is the real telltale, and it looks like new.  Should be well worth fixing up!

Trivia: they started work on the 8566A in the early 1970s, and it didn't ship until 1979.  Its code name was "Doomsday."  The earliest drawing I've seen is from 1971 (and never mind where it came from):

W4PJB:
That's a very fascinating site, thank you! Not surprised it was code named "Doomsday". It doesn't take a vivid imagination to figure out what kind of projects would have motivated development of a cost is no object, 22 GHz spectrum analyzer in the 1970's.

nctnico:

--- Quote from: W4PJB on June 11, 2024, 02:08:52 am ---Apologies for the weird color cast in right side of the photo, it's an artifact from the rolling shutter in my iPhone and the crappy fluorescent light above my bench. Everything inside is as clean and silvery as it should be :)

--- End quote ---
This looks like new indeed. I'll admit that looking at the photo of the internals does put a smile on my face  ;D

G0HZU:
Yes, it does look to be as new inside. I recently acquired a late model HP 8405A vector voltmeter that looks inside like it was made yesterday. It's absolutely sparkly clean inside.

To give some contrast, I know the history of my 1500MHz HP 8568B analyser back to about 1987 and it was made in 1986. It was donated (as part of a contract) to the company I work for back in about 1987.

I joined in 1990 and this analyser was used for >8 hours every working day for about 15 years since 1987. It was never used in an ATE rack so was switched off every evening. The company gave it to me (I made a small donation to a charity to secure it) in about 2005 after it had fallen out of use at work for a few years.

When I took it apart, I was surprised at how much dust there was around the CPU board. It was thickly coated in dust to the point it wasn't possible to make out the ribbon cables. The display unit showed quite a lot of black soot around the HT areas.

I'm not sure why it was so dusty and sooty after maybe 30,000 - 50,000 hours operation time. It may be that the filters in the fans weren't working well for many years or maybe there was more dust in the air than I realised in the RF labs at work!

My HP 8566B is a few years older but the display unit was very clean inside. Not nearly as sparkly clean as yours but I assumed that it had been internally cleaned and serviced at some point because it showed none of the soot and dust that I found inside the 8568B. I suspect that my 8566B has seen a lot of use as it was an ex-rental analyser from Microlease.

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