Someone gave me this unit last week. I've got no idea who made it and have never even used a cap leak tester before but it looks pretty simple. It uses a 5881 tube that tests good. I did replace a large 470K , probalby 2 watt resistor since the original measured way low. Don't laugh that I had to use three separate resistors in series to hit 470K. I didn't change the 20mF 600V electrolytic since I couldn't justify the $15 price at Mouser.

In use, the DC volt meter is fairly accurate but does not reach much past 600V at max setting. Maybe that's all it was designed for. Testing an old crusty cap did show good movement on the leakage meter with a corresponding illumination of the lamp under the chassis. So I assume that's an indication of a leaky cap. I don't really know what amount of leakage if any, is acceptable when using a meter like this. Now to demonstrate my ignorance and ask a question: Should this type of tester work for electolytics? I see leakage currrent whenever I test even new electrolytics well before they reach their rated voltages.

Here are some pictures. I do like the green power ON lense, that's a nice touch.

From the looks of the chassis, it looks like something that was custom made by some company for QC or assembly line
testing. Some of my jobs were designing and building test equipment such as that one.

It's rare that a high wattage resistor would go down in value, generally they go up. The one component that I would have
changed right away is that electrolytic cap, as it might wake you up with a loud bang one of these days if it doesn't take
the power supply out first.

Looks like a well built piece of gear, enjoy it!

Opps, I should have said the 470K resistor went up, NOt down in value. It measures 620K. 20mF 600V elecrolytics are a bit pricey, that's why I heisitated to order one until I'm sure it's needed. So do you think this rig is designed to test electroylics as long as you follow polarity?

Considering the current range of the meter I would say it was made for testing electrolytics; 30 ma (or even 1 ma) would be way too high for mylar or poly caps today.

If the voltage output is fixed and goes to 600 on the 1000 volt range that would limit its use. You would not want to put 600 volts on a 450 volt cap. 100 volts would be too low for a proper test also, even for a 160 volt cap.

You could use a pair of 40 mfd. 450 v caps in series with about a 27.k 5 W resistor across each one to balance out the voltage drops. Those would be a lot cheaper than 750v or 600v caps.

Johnnysan, the voltage is controlled by a combination on/off switch (on the let) with rheostat so it can be gradually controlled to whatever voltage you desire depending on the range selected. So using the range, it can be dialed into any voltage starting at zero but on the top range it maxes out at about 600V with the knob turned all the way to the left.

Unusualdesigner, I guess I'll have to fiddle with it some more and pehaps sub in new electolytics per your suggestion.

When testing caps for leakage do you usually leave it on for a few minutes waiting for an indication to crop up or are faults found right away?

When testing new non electrolytic caps and limiting the voltage to the appropriate level, I see no leakage, but when testing new electrolytics I always see leakage, with a corresponding illumination of the bulb under the chassis, that's why I was wondering if perhaps this wasn't designed for them.

Your right about the the testing, JAN Spec C-62 is for "Dry Electrolytics, Polarized". Probably built for testing caps for a military project, if you look under the leakage meter it lists the leakage limit as ".04 x C +.5".

I don't think it's fixed voltage, the lower left control probably adjusts voltage across the cap under test, lamp under chassis maybe a fuse.

I would think that the lamp under the chassis is used as a current limiter similar in function to a dim bulb tester.

Alan,

Better idea....

Forgot to mention it does have a fuse.

Some interesting comments on C-62 here.
http://www.mail-archive.com/amradio@mai ... 21215.html
Hank

New electrolytics are usually down in the micro amp range. This must be a very sensitive tester. It must use the tube to amplify the leakage sensitivity. I would try some high ohm resistors to to see what it takes to move the meter to different points.

Wonder why it needs a 6L6?

If you have a leakage tester with just a meter and power supply it can be easy to zap the meter with a shorted cap. If the internal resistance is too high it can take a long time to charge up a large electrolytic. By using a tube to drive a meter you can limit the current and also increase the sensitivity. I like my Heathkit IT-28 because it has very good sensitivity with 3 ranges and there is no meter to burn out or act up with sticking and such.

The 5881 is probably a grid-controlled rectifier, a simple way of getting a variable DC voltage but the regulation is terrible. The switch is for meter range and has nothing to do with setting the voltage. If you can't see 10 microamps on the meter (and 1 microamp would be preferable) then this is pretty much useless for modern electrolytics. Any electrolytic that passes a milliamp goes straight into the trash. Actually any that passes a tenth of that (100µA) goes into the trash. That mil spec is fifty years out of date.

Edit: you beat me to it.

I think that thing was made for oil filled metalized paper capacitors used in an
industrial setting We made one up like that to test oil caps in induction heater
modules (there were 40 1.5 kW modules on a machine).

Occasionally one would one would trip on the fly and was swapped out.

After a while there would be a bunch of modules to be repaired and
returned as spares, and the capacitors were the leading cause, but tricky
to find because the modules would work fine on the test stand.

The leakage test gave an indication.


Eventually the capacitor maker said that series of caps needed to be all

changed out of service. Ours weren't paper, plastic of some sort.

I agree the tube is used as a grid controlled rectifier and the switch controls the range of the voltmeter. Although the milli-ammeter range is from 0 to 30 ma., an external micro-ammeter could be used in conjunction with this instrument to measure the leakage current of modern capacitors. However, care should be exercised to avoid overloading the micro-ammeter.

Interesting discussion, but I think many would agree that any "Antiques" involved on this forum have capacitors that are
either bad or time bombs.

Thant being said I still use an ancient bridge to test recent production caps before replacement.

Mostly what happens in a Pyranol capacitor stays inside a Pyranol capacitor.