[ARC5] Cap Test

[Kenneth G. Gordon]

On 8 Feb 2011 at 11:55, Robert  Eleazer wrote:

> And moving on now to less philosophical, and one would hope, less
> controversial realms, I wonder if anyone can recommend a quick and
> dirty test for electrolytic caps.

Hello, Wayne: I can recommend several different ways, from ancient to 
more modern. 

There were several different companies which made effective cap testers. 

Among them, Heathkit (several models), Knight, Sprague. I have two 
Heathkit C-3s which I rebuilt and wrote an article on which was published 
in Electric Radio magazine some time ago.

The Sprague Tel-Ohm-Mike is among the best, the TO5 being the best of 
the bunch. I think Aerovox made a similar unit.

All of these can test caps at their rated voltage.

I also have an article on my website detailing "Reforming Electroylic 
Caps" from an older military manual. See that here:

http://www.w7ekb.com/glowbugs/Military/Military__and__Surplus.html

at the bottom of that page.

> Last night I turned not one, but two, 5Y3GT's into momentary night
> lights.

One of my BC-221 power supplies is doing that: in fact, it has ruined two 
5U4s. I have not dug into it yet, but I suspect an intermittant short in a 
cap.

> I am trying to figure out why and I'm trying to decide if the
> previously satisfactory replacement electrolytic filter cap has turned
> violent.

Although that could be, I would suspect something in the attached 
equipment instead, or an intermittant short in the power transformer.

> Normally I charge up a cap, remove the power and see how long it takes
> for the charge to dissipate. Instantaneous loss of voltage is bad. If
> it lingers on a while, slowly decaying at a steady rate, that's good.

Well, IMHO, that is a rather crude way of doing it, and is fraught with error 
possibilities.

One of the newer ESR meters would be an excellent choice. There are 
several small companies that make kits for those. I have one of those 
here, but cannot remember the name at this point.

The Heathkit IT-28 or IT-11 are excellent too, available on eBay at regular 
intervals.

Ken Gordon W7EKB