[Amps] .01uf caps across diodes ?

[MU 4CX250B]

Hi Bill, I remember that argument,too,  but It doesn’t carry much
water with today’s uniform components. The back resistance of a series
string of diodes is so high that I doubt an uneven capacitive voltage
divider would cause problems. Normally one designs an HV diode bank
with at least a breakdown voltage safety factor of 2, and preferably
more.
73,
Jim W8ZR
Sent from my iPhone

> On Dec 12, 2022, at 10:19 AM, hzp_electronics at juno.com wrote:
> 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 at miamioh.edu>
> To: Tim Duffy <k3lr at k3lr.com>
> Cc: jim.thom at telus.net, amps at 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 at k3lr.com> wrote:
>>
>> W8ZR Jim
>>
>> Can you give advice on this topic?
>>
>> 73
>> Tim K3LR
>>
>> -----Original Message-----
>> From: Amps [mailto:amps-bounces at contesting.com] On Behalf Of jim.thom
>> jim.thom at telus.net
>> Sent: Tuesday, November 29, 2022 2:28 PM
>> To: amps at 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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