I have various piles of old caps, many NOS, etc. I'm interested in doing a simple go/no-go type of test for leakage.
Have power supplies that can do 0 to 3kV DC.
Is it practical to put the cap in series with a microammeter (mechanical, to not risk damage to a DVM) and a current-limit resistor, then just dial up the voltage up to the rating of the cap (or beyond)?
One part of my question is: When (for example) a paper coupling cap goes leaky, just how leaky is it?

If a (for example) 20uA full-scale meter would not be sensitive enough, perhaps I set up a triode tube with a rather high-value grid R, and see if a leaky cap is able to change the bias.

Thanks for any comments!
Pete

On 2022-11-29 9:29 p.m., saipan59 (Pete) wrote:

I have various piles of old caps, many NOS, etc. I'm interested in doing a simple go/no-go type of test for leakage.
Have power supplies that can do 0 to 3kV DC.
Is it practical to put the cap in series with a microammeter (mechanical, to not risk damage to a DVM) and a current-limit resistor, then just dial up the voltage up to the rating of the cap (or beyond)?
One part of my question is: When (for example) a paper coupling cap goes leaky, just how leaky is it?
If a (for example) 20uA full-scale meter would not be sensitive enough, perhaps I set up a triode tube with a rather high-value grid R, and see if a leaky cap is able to change the bias.

Mr Carlson's Lab has published a design for a device for making this test that seems to work well (based on his videos).



--T

Thanks for any comments!
Pete

Hi Pete & All

I, too, am interested in this and have been thinking about building a leakage tester.? I had one years ago, back in the days of valves, that used a 'magic eye' as the leakage detector, although I often suspected that test equipment might have been leakier than the things it was testing!? I shall follow this with interest.
--
All the best

Richard M0RBF

On Wed, Nov 30, 2022 at 07:06 AM, Toby wrote:

Mr Carlson's Lab has published a design for a device for making this test that seems to work well (based on his videos).

?Mikek

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Unless you want to repair early tube equipment you should hardly need a leakage tester. If you do deal with early tube equipment then replacing all paper capacitors with plastic film types is a sensible start. A regular 20K/V meter on a voltage range will indicate 0-50uA leakage and have series protection. Most bench DMM's are 10M ohm Rin with a basic 200mV FSD.

If you put a suspect cap in series with a DVM and a power source you can start on a suitable V range then switch to current if needed. On a voltage range with 10Mohm input you are also seeing 0.1uA/Volt. Putting 1.1 Mohm across the terminals as a shunt gives 1uA/Volt, 100K gives 10uA/Volt. So I don't think a leakage tester is very useful apart from mains leakage which is another matter.

What is FAR more useful is an ESR meter. Most electronic equipment made in the last 20 years? fails because of electrolytics loosing capacity through loosing water, often the can ruptures or detaches. Many PC motherboards kill CPU's because of cooked electrolytics. The ESR meter allow very fast testing of electrolytics and the detection of failing parts before they do extensive damage. Many CCFL's fail because their reservoir capacitors fail, many wall warts fail for the same reason, the result is pulsing the equipment at double line frequency which will often cause a processor to be reset very rapidly.

ESR meters measure impedance with a low voltage but relatively high current signal around 10-50KHz,? Testing is mostly in-place i.e. mostly no de-soldering is needed, with a good tester it should be possible to check a capacitor in a few seconds.

Regards, Alan G8LCO

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Thanks for the comments/links so far.

The "Mr. Carlson" stuff: I watched his very 'wordy' video, where he repeatedly says how awesome his tester is, how carefully he has tested his design, and he demonstrates it over and over, and shows us how the old magic-eye-based testers are dangerous and inferior. I went to the Patreon page to find out how it works, but found nothing but buttons to click to send $money$. Annoying. I don't care about seeing his Top-Secret schematic, but would anyone be able to explain how his design works? In particular the "forecast" mode - is he doing something very special/clever?

Anyway, I gather that the two methods I proposed in the first post are fine. Alan's suggestion of using a VOM sounds practical and easy.

Pete

Just tried a few. Using an HP power supply that does 0-320V, with the current limit set low, and a Simpson 260 VOM on the 50V or 10V scale.
Seems to work well.
Here's a pic - good on the left, bad on the right.
Some of the 'bad' ones are perhaps marginal - a very small deflection on the meter.

BTW, I hope I didn't offend with my criticism of Carlson. He has every right to protect his I.P., to "sell himself", etc. I just exercise my right to ignore his content.

Pete

BTW, one of the worst ones of this bunch was equivalent to a 6M resistor (tested at 300V, cap rated for 400V).

Pete

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I used to supervise a service team of 14 guys and other things. Carlson would not have been one.? Servicing is about probability, experience and logical inference but it all needs to be based on sound theory, you also need to take less than a month to fix things, glacial is not an acceptable speed setting. Droning? on and on about outer foil? again and again and again shows a lack of focus on what matters at AF & LF in the crap he deals with. But it must impress someone.

Capacitors are usualy very reliable but 60 year old paper dielectrics are often way beyond their use by date, there's not much point in NOT replacing such parts unless you have a stationary exhibit in a museum. Any old electrolytic also qualifies for retirement. Why would you leave a part known to fail in place only to have to change it some time soon? For a lot of Tube gear the big issue is with AF coupling caps, there are not that many, replacing old paper caps with modern plastic film types is a no-brainer providing that you can get decent replacements. If you speak to people used to servicing particular gear they may let you know particular liable to fail parts. Stock faults are common to all kinds of electronics, there used to be particular brands which were more liable to cause problems. Long time back there were some electrolytics in plastic cases that were very unreliable. One of the causes of electrolytics failing was sweat, one trace on a foil or paper would condem the part eventually. Bead tantalum capacitors are another "Replace on Sight" part, they fail to a very short circuit. On the other hand mil spec tantalums in cans are very reliable, the flat disk "acid" types are possably the best electrolytics ever made, now at ransome price levels.

An ESR meter needs to deal with series resistances? under 0.2 ohms for larger caps ( e.g. 220-4700 uF). The failure is mainly due to ripple current at high operating temps or running cheap electrolytics where higher rated parts are needed. So a useful ESR meter needs to read down to 0.1 ohms or lower.? It also needs to be fast settling in a pro setting, waiting more than a second or two is as useful as toothache when you want to check every at risk part. I used an Electronic Design Specialists EDS 88A when I was doing it for real, that was a very effective tool. ESR meters are absolutely vital when working on switch mode supplies. Now for a True Story about ESR.

There was one product that failed after 6-18 months, we had about 800 in the field. It was a CRT monitor. It would fail with extensive damage to the Flyback Transformer and shorted Horizontal Output transistor.? If you replaced all of the failed parts it would work again then 1-30 days later you needed to replace all of the parts again. The ESR meter found a small 22uF cap in the switching supply that had high ESR. When I checked the part it turned out that the manufacturer had changed the part, the new part had a smaller can.? Smaller can = lower ripple current rating. After a while the capacitor ESR went higher when the product was warm causing the rail to the Horizontal output to increase and do extensive damage. Turns out that some "Value Study" had saved a few cents on one cap without checking the consequences. That cost the Company it's reputation that had developed in 50 years of manufacturing.

I still use the EDS88A, but also have a? Vanwell Chinese multi-function tester, it's surprisingly good for many semiconductors and will indicate ESR for electrolytics down to 0.1 0hms. It's? too slow for pro use but much better than toothache, good for hobby users and very inexpensive.But a lot of dirt cheap Chinese RCL meters that I have seen are very inaccurate. For RCL indications for rough work? I use a Peak LCR45, that has a good wide autorange for AF and RF use and is accurate.

Regards,

Alan G8LCO

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Hello Jeff,
I understood "bumble bee" capacitors to be a style of capacitor made
by Mullard, certain values have colours which are similar to? those
of a bumble bee. I see them on ebay advertised as "tropical fish"
capacitors, probably for the same reason.? One advertiser is asking ?250
for 4 of them !!? In the hi fi section of course.
If he sells them I stand to be a millionaire as I've got 100s NOS.
Regards Ken g8beq