Hi Tim,
Years ago I built a receiver and needed a power supply but the transformer I
had was to much voltage. So rather than just a capacitive input filter I put
a choke of a few henrys between the diodes and the filter capacitor to drop
the voltage some. That worked fine but I had this hash noise that I couldn't
find. Turns out it was rectifier hash. I put a .o1 or .02 capacitor on the
input side of the choke go B-. That solved the problem of the hash from the
rectifiers.
Most amp power supplies are capacitor input type so the filter cap absorbs
the diode switching transients.
Back in the early days of solid state diodes I remember it being recommended
that they should not be used with a choke input filter.
The only amps that I can think of are the Henry amps that have a choke input
in the filter. However they use a tuned choke so there is a capacitor across
it which effectively shorts any transients to the main filter capacitor.
73
Gary K4FMX
> -----Original Message-----
> From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Tim Duffy
> Sent: Tuesday, December 13, 2022 7:39 PM
> To: 'Ron W4BIN'; 'amp'
> Subject: Re: [Amps] .01uf caps across diodes ?
>
> My question around the .01 uF caps on the HV rectifier diodes
> was not so much about diode preservation or protection - I am
> curious about any possible RFI generation from the HV diodes
> or more importantly any mixing products from RF (multiple
> transmitters). So a .01 uF across the HV diodes or .01 uFs to
> B minus on the diodes that might "keep things quiet" is my curiosity.
>
> 73,
> Tim K3LR
>
> -----Original Message-----
> From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Ron W4BIN
> Sent: Tuesday, December 13, 2022 7:53 PM
> To: amp
> Subject: Re: [Amps] .01uf caps across diodes ?
>
> MU 4CX250B wrote:
>
> > An interesting point, Steve. If I understand you, you're
> saying that
> > if a modern diode in a series string approaches reverse
> breakdown, it
> > will start to conduct, thus shifting its overload voltage to other
> > diodes in the string. Before the advent of controlled avalanche
> > diodes, however, an overloaded diode would just short circuit, thus
> > permanently shifting its voltage to the remaining diodes in the
> > string. This process, once started, would likely lead to the
> > destruction of the entire string. To me, the takeaway
> message is that
>
> No that has never been the case, "controlled avalanche
> diodes" of a particular type all avalanche at the same
> Voltage.* Otherwise the lowest reverse Voltage device could
> avalanche and present a very low resistance, (causing an
> increase in reverse Voltage across the
> rest)
> then the next lowest Voltage device could avalanche until
> they would all avalanche at which time, the current would
> destroy most until one "blows open"
> ending the catastrophe.
>
> Zener diodes below about 6.2 Volts are true Zener diodes,
> above about
> 6.8
> Volts are "controlled avalanche diodes" and as long as they
> are conducting reverse current less than Imax they are not harmed.
>
> * in our high Voltage operations a tighter grouping of
> avalanche Voltages can be maintained by buying in lots like
> of 50 or 100 and keeping the batches separate and
> constructing strings all from the same batch.
>
> > there's little to be gained these days by adding .01uF caps to each
> > diode. This is a helpful explanation, Steve. Thanks!
>
> --
> Ron W4BIN - Understanding is much better than
> knowing how.MX
>
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