[ARC5] capacitor leakage

Wed, 05 Feb 2003 20:41:56 -0600

I looked at the schematic for my Eico 950B cap bridge.  From that circuit 
the eye needs -8V on the grid to completely close which shows a good amount 
of leakage.  In order to obtain this the capacitor would have to leak 18uA 
(yes that's micro) at about 500V.  This corresponds to an insulation 
resistance of 29 meg ohms.  This should give some sort of idea on what kind 
of currents and resistances we're looking at to determine if a cap is leaky.

Sean

>From: Jim Mandaville <[email protected]>
>To: [email protected]
>Subject: [ARC5] capacitor leakage
>Date: Wed, 5 Feb 2003 15:02:07 -0700
>
>Stew Beckley writes:
>
> >Now for the question I haven't seen answered: What IS the acceptable
> >leakage current per cap in those old triple-05's? I suppose there are two
> >values worth quoting: a)The "spec" value for that particular cap (if
> >anyone has the parchment on this), and b) an empirically derived value 
>for
> >proper and safe operation in a command Tx or Rx.
>
>I thought I would be able to contribute something on this from the manual
>for my Heathkit IT-28 capacitor checker.  But I can't find the manual for
>this (and perhaps never had one).  By the way, when I restored this very
>useful instrument (not  to be confused with some other Heath models with
>less capability) I found that the various voltages applied to capacitors
>for leakage checking were far out of specs due to resistors in the divider
>chain changing values; had to replace several resistors.  Anyway, the
>"magic eye" tube used in this instrument to show "unacceptable" leakage at
>rated voltages has different bias settings for different capacitor types,
>and the designer must have had some data on what was acceptable for each
>type.  This might have been in the manual for the IT-28, so anyone with the
>manual might have a look.  Or (if I were more ambitious) I could push a
>paper cap to the "unacceptable" leakage point and check that with a
>microammeter).
>
>By the way, when I put some of my ARC-5 ancient caps on the bridge of the
>IT-28 they generally showed MORE
>capacitance than their labels, often twice as much (I know from new caps
>that the IT-28  bridge is accurate).  Most of the caps showed " Heathkit
>unacceptable"  leakage when I got up to about the 100 v level.
>
>Jim
>
>
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