Hi Jim
The best argument that I have heard about capacitors across diodes is that
older diodes had uneven capacitance. Under certain conditions the capacitance
would cause the voltage to divide unevenly between the diodes. The added
capacitors were made large enough to swamp out the capacitance difference and
keep the voltage division more equally.
\
Whether the caps are needed with modern diodes, depends!
73
.... Bill K3HZP
---------- Original Message ----------
From: MU 4CX250B <4cx250b@miamioh.edu>
To: Tim Duffy <k3lr@k3lr.com>
Cc: jim.thom@telus.net, amps@contesting.com
Subject: Re: [Amps] .01uf caps across diodes ?
Date: Sun, 11 Dec 2022 22:32:29 -0800
Hi Tim,
I’ve followed this debate for years and frankly I don’t think adding
.01uF caps across each diode in a diode string makes much difference
one way or the other. It’s true that there will be some suppression of
fast current and voltage transients, but these aren’t likely to cause
damage to modern components. To me the downside of the practice is
that adding 0.01uF caps results in additional opportunities for
capacitor failures, loose solder connections, unsightly wiring, and a
bunch of extra components that provide minimal benefits. I’m inclined
to leave them out. (BTW, one commenter suggested that sharp voltage or
current spikes wouldn’t make it through the filter capacitors. That’s
untrue because the filter caps have a self inductance that keeps them
from filtering spikes with high frequency components. )
73,
Jim W8ZR
Sent from my iPhone
> On Dec 11, 2022, at 7:03 PM, Tim Duffy <k3lr@k3lr.com> wrote:
>
> W8ZR Jim
>
> Can you give advice on this topic?
>
> 73
> Tim K3LR
>
> -----Original Message-----
> From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of jim.thom
> jim.thom@telus.net
> Sent: Tuesday, November 29, 2022 2:28 PM
> To: amps@contesting.com
> Subject: [Amps] .01uf caps across diodes ?
>
> What's the consensus on wiring .01uf disc caps across diodes in a HV supply
> ?
> W8JI sez they are required, and used in ameritron amps....and used to
> eliminate switching transients.
>
> Some say the caps are required to meet emc specs on commercial gear.
>
> I can't see how anything can get past the HV fitter caps.
>
> KM1H also uses caps across diodes. He also used another method, with a
> .01uf cap across an entire series string of diodes, like a .01uf @ 5 kv
> type.
>
> Orr's books recommend caps across diodes... to eliminate noise on TX on
> ssb. .
>
> Are they required...or not ?
>
> Jim VE7RF
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>
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