[Amps] HV Supplies and Diodes

[Bill Fuqua]

    Sometimes it is good to remember the "old ways". I recall a few years 
ago visiting  a tube audiophile who built an all tube stereo system using 
866 rectifiers and 805 output tubes. They could not understand why they 
were constantly replacing 866 tubes. They had a capacitive input filter. 
Also, in the old  days most HV  power supplies had inductive input filters. 
Not only did they not blow away the mercury rectifiers they provided better 
output voltage load regulation and lower peak current on the power lines.
    I seem to recall special solid state diodes made to be used with out 
the RC networks that had "controlled avalanche". These all had identical 
reverse break down voltages.
    Are there any application notes that tell you how many 1kV PIV 
rectifiers one should place in series for N*kV PIV . The number should be 
greater than N.
But by how much?

73
Bill wa4lav


At 07:51 AM 1/3/2008 -0500, you wrote:
>It's the safety issues that worry me most of all.  Having been through the 
>mill of UL, CSA, CE etc when designing products for sale, I know it is a 
>complex subject and common sense does not always lead to a safe solution, 
>ie you need hard knowledge like creepage and clearance distances, 
>insulation breakdown etc.
>
>David
>G3UNA
> >
> > From: "Roger" <sub1 at rogerhalstead.com>
> > Date: 2008/01/03 Thu AM 02:20:10 GMT
> > To: <amps at contesting.com>
> > Subject: Re: [Amps] HV Supplies and Diodes
> >
> >
> >
> >
> > >I find it a bit strange and somewhat comical that the only ones that 
> appear
> > > to champion resistors and capacitors across any series string of 1N540x
> > > diodes is the amateur community.
> > >
> > > Not one manufacturers application notes mention them.
> > >
> > > No industrial product that Im aware uses them.
> > >
> > > The one ham amp manufacturer mentioned has a reputation of power supply
> > > problems.
> > >
> > > Most of us realize that the diodes of the 60's had problems but is there
> > > any
> > > reason to continue it almost a half century later?
> > >
> > > Fact or mythology?
> >
> > Neither. It's History and background. Most of the current crop of hams have
> > been around long enough that's "the way things were" and unless a person
> > keeps current they will still tend to think in the way they were taught.
> > Early on we might build a PS.  The last one I built was close to 30 years
> > ago when diode strings were big stacks of diodes, resistors, and caps as
> > were the "potted" commercial replacements for vacuum tube rectifiers. I
> > think you will find well over half the hams around now still think in the
> > same terms. Also take a look at the diode stacks on all but the more recent
> > amps you are likely to find in most stations.  The only amp I own that is
> > less than 20 years old is my new solid state Tokyo Hy-Power HL1.5Kfx.
> > That's why I deferred my comments to the "Handbook". IOW, check the
> > "Handbook" for proper design.
> >
> >
> > Roger (K8RI)
> >
> >
> > >
> > > Carl
> > > KM1H
> > >
> > >
> > >
> > >
> > >
> > > ----- Original Message -----
> > > From: "Jim Tonne" <tonne at comcast.net>
> > > To: "Dennis W0JX" <w0jx at yahoo.com>; <amps at contesting.com>
> > > Sent: Wednesday, January 02, 2008 2:20 PM
> > > Subject: Re: [Amps] HV Supplies and Diodes
> > >
> > >
> > >>
> > >> When a string of series-connected diodes is reverse-biased
> > >> (during part of the cycle), the voltage drop across one is
> > >> proportional to its leakage resistance.  If the junction of the
> > >> diode type has significant capacitance, then that enters into
> > >> the picture too.
> > >>
> > >> If you use, in parallel with each diode, a resistor whose value
> > >> is a fraction of the leakage resistance, then those resistors will
> > >> swamp the leakage and so tend to equalize the voltage drop
> > >> across each diode in a string.
> > >>
> > >> If you use, in parallel with each diode, a capacitor whose
> > >> value is several times that of the junction, then those capacitors
> > >> will swamp the junctions and again tend to equalize the voltage
> > >> drop across each diode in a string.
> > >>
> > >> During the forward-conduction part of the cycle of course
> > >> we have no problems with any of the above.
> > >>
> > >> I am not familiar with the rules on avalanche diodes.
> > >>
> > >> - Jim WB6BLD
> > >>
> > >>
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> > >>
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