Re: [EE] solid aluminum caps on 60hz

I came across this also - Diodes generating RF at around 150MHz. Fixed with
a snubber across the diodes.  We put it down to reverse recovery time of
the diodes. As Dave noted above, noise sync'ed wih the switching rate was
the clue. From memory they were 'ultrafast" Si diodes due to the
voltage/current/cost/availability limitations at the time.
RP

On Sun, 18 May 2025 at 03:56, David VanHorn <[email protected]> wrote:

> I've seen it up in VHF, and small caps like 1nF across the diodes
> eliminated the problem.
> The clue was that the interference was exactly synced to the line
> frequency.
> I don't know what the actual mechanism is that causes the problem, possibly
> the reverse current charging the junction capacitance? Swamping out that
> capacitance would lower the frequency of the RF.
>
> On Thu, May 15, 2025 at 9:55 AM RussellMc <[email protected]> wrote:
>
> > On Fri, 16 May 2025 at 03:48, John Lawton <[email protected]> wrote:
> >
> > > I experienced interference on a nearby AM radio, IIRC the cure was to
> > > add a capacitor across the transformer secondary.
> > >
> > > A series resistor from diodes to cap spreads the conduction angle.
> >
> > Effect of cap across transformer "would need thinking about".
> >
> > In ye good olde days with high voltage tube supplies (807s at 1200V?) it
> > was not uncommon to see diode strings (to achieve high enough voltage)
> with
> > resistors in parallel with each diode. I'm getting old :-)
> >
> >
> >              Russell
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