[Test-Equipment] Sprague TO-6A question

[Ken Kaplan]

Yes, I checked the old C16. It measures 50K which I think means 50K 
megohms or 50 gigohms. Seems like enough but I guess not for the 
circuit. The new replacement indicates infinity. I know the other tests 
are not of much value but I wanted to gather as much info as I could. My 
new replacements are Mallory metalized polyester. You think polyethylene 
film would be better?

Ken

k4pf at juno.com wrote:
>
> Hi, Ken
>
> Glad to help!
>
> Did you try measuring the insulation resistance
> of the removed C-16 cap with the fixed Sprague TO-6?
>
> An ESR meter isn't a good check 
> for a small paper capacitor, because everything except
> a shorted cap will show up as >99 Ohms.
>
> A digital capacitor tester is also not a good test
> to find leaky capacitors.  Try it with a good mica 
> or ceramic capacitor and see how little the reading will change
> with a parallel 1 Meg resistor added. 
> My B+K model 830 digital capacitance meter is useless in this regard.
>
> The Sprague tester does very well at spotting leaky paper capacitors:
> You will see that the eye tube doesn't indicate a sharp null,
> it is as if the null were diffuse, smeared around the dial
> when doing a capacitance measurement on a leaky paper capacitor.
>
> One hint: don't forget to renew the paper capacitors used
> as the "standard" capacitors C-9 and C-10 in your Sprague TO-6A,
> or even a perfect test capacitor may produce a diffuse null.
> Polyethylene film caps would be a good choice for the standards,
> and you can use your digital capacitance meter 
> to select the standards for high accuracy before installation.
>
> 73,
> Ed
>
>
>> Ken Kaplan <krkaplan at cox.net> wrote
>
> You got it! I should have looked at the schematic but I think I got a 
> bit lazy. Actually I was in the process of recapping a Hallicrafters 
> SX-100 & thought I'd test what I had just removed. Looks like I better 
> recap the TO6 first. If the test equipment isn't any good, there's no 
> point in digging into the radio.
>
> Funny thing is I tested C16 after installing its replacement and it 
> looked ok. I measured its value on a digital tester and it was within 
> 10%. I checked its ESR and found that it was > 99 ohms. 
> So I don't know what to think.
>