>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@comcast.net>
> To: "Dennis W0JX" <w0jx@yahoo.com>; <amps@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
>>
>>
>> _______________________________________________
>> Amps mailing list
>> Amps@contesting.com
>> http://lists.contesting.com/mailman/listinfo/amps
>>
>
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|