I am the proud owner of an HP-8640A . I received?it with a couple of faults (no AM modulation, no FM deviation).

I repaired it by myself and now it works perfectly.

Its a good instrument with very low phase noise. It drifts, of course it's a free running generator and the stability in not comparable with a synthetized?one

we are talking of an hundred herz / hour.

The nice aspect of 8640A is that the switching wafers are old style ones and they haven't the fingers mounted to a plastic disc, so they dont?brake.

Il giorno dom 23 gen 2022 alle ore 04:43 Stuart Landau via <stuartl73=[email protected]> ha scritto:

I have never actually seen an HP 8640A. I think that few were made; a great many 8640B generators were made.

I have also worked on many of the USM-323 military signal generators; it is a rugged 8640B without some of it's features. They have a frequency counter but there was no provision to frequency lock the signal generator. They are fairly stable after an hour warm up, in a temperature stable environment. The 8640B will not stay frequency locked for a long time; when the UHF oscillator drifts, you will have to relock the generator.?

The big advantage of the 8640 series over many frequency synthesized signal generators is its low phase noise. A disadvantage is that you have to do a lot of cranking of the tuning knob. That soon gets old.

The use of a lot of nylon gears in the 8640 signal generators dooms many of them to the scrap heap, after decades of use.

Stuart K6YAZ

Los Angeles, California?