Re: [Amps] Shunt resistors for a bridge made of 6A10 diodes

["Carl" <km1h@jeremy.qozzy.com>]

I went with the caps BECAUSE I DID see some spikes on the line with a scope 
and the filter caps were fine. Another went from the output of the doubler 
to ground. No more hash.
Carl
KM1H


----- Original Message ----- 
From: "Gary Schafer" <garyschafer@largeriver.net>
To: "'Amps group'" <amps@contesting.com>
Sent: Tuesday, February 09, 2016 12:52 PM
Subject: Re: [Amps] Shunt resistors for a bridge made of 6A10 diodes


> He is talking about one capacitor for each "leg" of the bridge not a
> capacitor across each diode.
>
> However you do not need any capacitors across anything when using a full
> wave bridge or voltage doubler. There is always a filter capacitor across
> every diode string.
> With a full wave rectifier there is not always a filter capacitor across
> each leg on half cycles.
>
> Power line spikes are not going to get thru the filter capacitors and
> transformer. Try measuring with a scope across a large filter capacitor 
> with
> a pulse generator and see what you get.
>
> Capacitors or resistors across each diode can introduce unbalance in the
> string unless precision components are used. Any unbalance in the string
> will force higher current in a diode than there would be without any
> resistors or capacitors.
>
> With just the diodes in the string the maximum PIV will be the sum of ALL 
> of
> the diodes PIV because of the avalanche effect of each. You will not 
> attain
> that with resistors or capacitors across the diodes.
>
> 73
> Gary  K4FMX
>
> > -----Original Message-----
> > From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Bill Turner
> > Sent: Monday, February 08, 2016 6:26 PM
> > To: Amps group
> > Subject: Re: [Amps] Shunt resistors for a bridge made of 6A10 diodes
> >
> > ------------ ORIGINAL MESSAGE ------------(may be snipped)
> >
> > On Wed, 3 Feb 2016 05:35:57 -0800, Jim wrote:
> >
> > >##  KM1H and a few others  will  use a single disc ceramic cap, like a
> > 4700 pf @  5/10 /15 kv variety...across  each leg
> > >of a FWB, so any transient  will simply go through the cap...vs the
> > diodes.
> >
> > REPLY:
> >
> > If you're going to do this, the capacitors should be closely matched
> > for capacitance  lest you introduce even more variation across the
> > diodes. Capacitors will divide AC just as if they were resistors.
> >
> > 73, Bill W6WRT
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