[Heathkit] HW-16 hum

[Tom NØJMY - AAR7FV]

Well...in Ken's case (HW-16) there isn't a regulator.  The caps across 
the diodes is a good idea, although I know Ken is usually a fanatic 
about doing that already.    Depending on how old the diodes are, maybe 
some equalizing resistors in parallel?  (The HW-16 uses a voltage 
doubler with two pairs of series connected diodes.)

Hey Ken, I just happened to think of something.  Is this the rig you put 
those humongous filter and doubler caps in?  Do I recall that it's 
possible for that to cause a very short conduction angle which, in turn, 
draws very heavy current in short pulses from the trans?  Or did I dream 
that?  Could that possibly be a factor here?

On that hummer I told you I'm working on tonight, I turned it on, let it 
warm up and then cut-off the heater voltage...the hum remained until the 
audio faded out, so it's not heater induced.  Hmm.  Or maybe I should 
say hmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm.

73,
Tom

Kevin Ward wrote:
> This sounds a bit like the hum problems we have with direct conversion
> receivers.  Try a .01uF capacitor across each diode and one across the power
> supply electrolytic filter capacitor(s).  Those spikes are short rise-time
> events.  Think of them as a high-frequency component superimposed on the DC.
> The electrolytics have a very poor response to that.  Any good regulated
> low-voltage power supply has a small value capacitor connected across the
> terminals of the electrolytics to keep this stuff out of the regulator, a
> high gain device.  You want to keep it out of the audio chain, also high
> gain.
>
> Kevin  N2IE
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