I dont see anything wrong with a 5-10% variation in the voltage across each
cap in an amp with enough headroom. Individual capacity was all over the
place 25-50 years ago unlike today where 20% is the normal spec.
As some equalizing resistors do age it is always an increase and rather
uniform in my experience with the non carbon variety.....thats a reduction
in heat when they go from 50K to 65-70K as in the NCL-2000 for instance.
The 30K Heaths rarely budge.
I still say that going extreme in filter C is a waste of time in most off
the shelf amps. Ive yet to hear any audible ripple complaints about 80-150uF
caps used in strings in the old days. Going from 200 to 330uf as I do with
SB-220 repairs makes only a very slight PEP improvement; the transformer
isnt capable of more and its the same with many price conscious amps.
Now if you want to run strings of 2400-4700uF caps with your 253# Dahl iron
on a 3x10 or whatever that is your business.
Carl
KM1H
----- Original Message -----
From: "Jim Thomson" <Jim.thom@telus.net>
To: <amps@contesting.com>
Sent: Monday, April 12, 2010 6:26 AM
Subject: [Amps] HV lytic max V ratings..some notes
> Date: Sun, 11 Apr 2010 09:59:15 -0700
> From: "Bill, W6WRT" <dezrat1242@yahoo.com>
> Subject: Re: [Amps] HV lytic max V ratings..some notes.
>
>>
>>Yeah, that's what I was always lead to believe. I was told that it is
>>better to run your caps very close to their voltage rating. Dunno if
>>its a wives tale or not.
>
> REPLY:
>
> I was told that too, but never heard any real proof. The idea was that
> an electrolytic is not a static (pun intended) component. The
> electrolyte is chemically active and will gradually deteriorate if not
> run near it's rated working voltage.
>
> Possibly just an old wive's tale. If anyone has any authoritative
> source, please post it.
>
> 73, Bill W6WRT
>
> ## Well, I don't see any [ new and old] tech notes from any of the cap
> makers
> on this topic. I think a quick email to CD, etc.. would be in order at
> this point.
>
> ## bring up old caps, or old B+ supplies, or caps that have been used at
> no more than 75% of their ratings, etc... on a variac, in staged
> intervals,
> appears to work good. I still would not suggest running em at more
> than 90% of their ratings..esp in a series string.
>
> ## I could see where firing up an old B+ supply, where caps were run at
>>90% of their V rating could cause problems. You could end up with a
> scenario where the leakage current is initially sky high, and the ratio of
> bleeder current to leakage current is really low, too low. That, plus EQ
> resistor's that are not matched up... could easily lead to individual caps
> in the
> string, being well over their V rating. Instead, bring em up slowly on
> a
> variac. If the caps are real antiques, like > 25 yrs old, imo, you are
> better off to
> just re-cap the entire supply, put in new eq resistors, [100k-3 watt mof]
> , safety
> rvs diode across each cap... and new 1N5408/6A10's in the FWB/FWDoubler.
> Add some hv fuses.. and a Glitch R... and be done with it.
>
> ## all these old 200 uf caps were too small in value to begin with. The
> 560+ uf
> variety can easily be retrofitted in place. Carl is correct. get rid of
> the old 25-30k
> eq resistors. They just cook the caps.. and the resistors will have
> drifted anyway.
>
> ## EQ resistor's that are all over the place in value... will have V drops
> that are all
> over the map. The highest value eq resistors in the string will have the
> highest V drops.
>
> Jim VE7RF
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