Easy to build capacitor checker A must for checking parts .

[Michael Simos]

I recently built one of these testers. It works great and I've found it very useful as I work on a lot of vintage guitar amps and Leslie amps where the owners get upset if you recap the "tonestack". This way I simply unsolder one lead off the tagboards and check for leakage.

It also confirmed what I've always suspected--virtually every paper and wax cap leaks like a sieve as well as just about every Sprague "Black Beauty". Thank you all for a great circuit and a very, very, useful piece of test equipment.

Mike

[Norm Leal]

Hi

I built something like this only using a meter instead of neon lamp. You can just about read capacitor value by how far the meter deflects. With a good cap meter drops back to zero. A leaky cap continues to give a reading.
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Norm

[Mike Toon]

Not to hijack but....I see you have a description on the outside of the box. Can't tell you how many times I've picked up a project with a plug on one end and wires coming out the other and have to take it apart to find out what I built. I now use a silver Sharpie on those black boxes.

[amptramp]

I added something similar to my Heathkit VTVM several years ago. I added a tip jack on the back (there is sufficient space in the circular cutout on the back around the line cord to add small components) and connected it to the internal +70 VDC supply. I connected a test lead with an alligator clip to it and clipped the capacitor to this lead and the volts probe and measured the voltage on the DC volts scale.

The meter would deflect up to +70 briefly then decay back down. Since the input resistance is known (11 megohms), I could translate the meter reading directly into leakage current.

Some capacitors would decay down to zero or so close to zero that I could not see any deflection even on the lowest (1.5 volt) scale. Some capacitors hovered near ground but never quite made it. And shorted capacitors read +70 volts continuously.

[KyMike]

In the variable voltage tester circuit #2, why is the voltage adjusting pot connected across the ac line instead of in series?


Mike

[Curt Reed]

Because you want a voltage divider. Otherwise with nothing hooked to it, there would be full voltage at the terminals at all times, as there is no current being drawn to create a voltage drop.
Curt
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Curt, N7AH
(Connoisseur of the cold 807) CW forever!

[KyMike]

Ok, just curious. Thanks.


Mike

[Homer1952]

This looks like the ticket for me. I am rebuilding an old Sherwood tuner & am wondering about all the small caps. I did not see any comments about in/out of circuit testing. Must you disconnect at least one leg of the cap from the circuit? Thanx- Bob

[Homer1952]

Thoughtless question. It will be circuit dependent.

[Renslipevol]

Very nice thread! I have to build myself one.

Makes me wonder how many megaohms it would be before the neon light starts to break down. The neon bulbs I was looking at online don't show what the current is at breakdown; just design current.

I would have to be more than 59.999 Mohms for me to make it, my fluke can getem, although it won't test them at 300v
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