My HP 8660B (subject of the instability issue now resolved) includes option 003 which is compatibility with 48-440 Hz power sources.
The HP 8660B has a linear power supply (ca. 1970s, predates switchers), presumably to improve the ability of the unit to serve as ballast on a large ocean-going vessel, among it's other capabilities.)
Question is this - the machine emits an acoustic (audible) noise after being on for a few minutes. I didn't pay attention to this before, but realized that the noise may be associated with the wide-range AC mains frequency compatibility - I figured it was just plates in the power transformer rattling.
In my (now obsolete) work life (mostly in cable tv engineering), "ferroresonant" power transformers (used to adapt 60 Hz local mains power to the 60-90 Hz pseudo-sinewave power used in the cable tv hardline infrastructure to deliver power to inline amplifiers), the noise was similar.
Does this (acoustic) noise ring a bell with anyone? Should I be concerned? The machine doesn't appear to exhibit any operating problems related to this (and I doubt has anything to do with the now-mitigated PLL issue).
Thanks
Dave
