[Hallicrafters] Re: capacitor voltage ratings re-observed

[Mark Shaum]

> Ken comments:
> Now, after saying all that, although, IMHO, the person who asked the
> original question could probably safely use 450 WVDC rated caps to
> replace his 475 WVDC caps, doing so would probably shorten their
> normal life span, especially considering that our modern line-voltage is
> higher than the line-voltage was at the time his receiver was made.
>

Yes! If you measure the leakage current drawn by even a brand new 
electrolytic, you will notice that the current through vs. voltage applied 
curve begins to steepen significantly as you reach the maximum rated 
voltage.  On a new capacitor, this will still be acceptable for using the 
capacitor at its rated voltage.  Just keep in mind that more leakage 
current=more heat=shorter life.

Years ago I used to keep a cigar box full of electrolytics removed from 
equipment that checked fine as far as capacitance goes and  checked ok for 
leakage at half of their rated voltage.  They failed leakage tests at full 
voltage.  My thought was that I could use them in lower voltage circuits. 
My second thought later on was why would I even consider using a capacitor 
in any circuit that has already begun to fail?  They all hit the trash can. 
Nowadays I wish I had kept some of them for "restuffing" or perhaps an 
attempted reforming, but I'd still be nervous about using them in a valuable 
piece of gear.

I've used 450v caps to replace 475v caps only in cases where I have 
attempted to verify that the actual voltage across the capacitor do not 
exceed the 450v rating.  This is important with our Boatanchors running on 
higher than designed line voltages.  The  B+ in my HT-32B in standby when I 
first received it was over 900 volts.  This is definitely a case where a 
pair of commonly available 450v caps in series would not be a good choice 
for replacing that oil filled unit even though the manual sez the B+ should 
be 750v.

Series cap note: The Heath Apache used, depending on production runs, a 
series pair of 125 uf at either 475v or 525v ratings for the B+ supply.  As 
I have a shorted pair of these in my parts Apache, I may take one of the 
525v caps apart to determine if it is a single or pair in series. I suspect 
it is a single unit, and 525v may be quite close to the maximum rating 
available for a electrolytic of this type of construction per Ken's 
observations.

73! - Mark K9TR
http://www.qsl.net/k9tr