[time-nuts] HP and other equipment failure

[Poul-Henning Kamp]

In message <1371329221.83869.YahooMailNeo at web171902.mail.ir2.yahoo.com>, Robert
 Atkinson writes:

> While I agree with everything else you say, you CAN have too much
> filter capacitance. At least where dc rectifier / filter (smoothing)
> circuits are concerned. Increasing C causes increased ripple current [...]

And ripple current can be a major source of power-line frequency
noise in all electronics.

The main reason why switchmode power-supplies today (can) outperform
linear power supplies with respect to noise, is because the legally
mandated PFC correction eliminates the bridge-rectifier ripple harmonics.

I would not hessitate to use a good quality switchmode to replace
the linear supply in a HP5370B.

I did some experiments a couple of years ago, with an audio-amplifier:
I put a standard PFC corrector chip on the secondary side of the trafo.

The overall result was not satisfactory, but the 50 Hz "sneer"
we all know and hate was absent, and the "Tzoing!!!!!" power-on
mechanical shock from the trafo was also eliminated, as was the
consequent dimming of the lights ;-)

The main reason not to do this, is that you need some physically
gargantuan coils for a 10A+ PFC-switcher.


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