Capacitor Tester and Reformer Unit - Stefan Niewiadomski

[Radio Fixer]

Good cause too Alan.

Gary

[SurreyNick]

Thanks for the feedback and suggestions. The project is shelved as 'unnecessary' and I will instead re-stuff old cans with decent modern electrolytics.
Nick

[Yorkie]

The BVWS do some small insulated can type  single electrolytics for stuffing, but they're 25mm diam x 30mm long, so it would be a struggle to get two inside a double unit can, though I've not tried it. 

I've attached a pic of a single 16uF BVWS cap that I used. Otherwise, the Rubycon BXW ones illustrated in post #5  in the link below from Farnell will sometimes fit three to a can, side by side:

http://golbornevintageradio.co.uk/forum/...p?tid=3934

(The BVWS ones are of course only available to members, which not all restorers are).

It's worth adding that the (non electrolytic) BVWS metalised polyester film caps are physically small and ideal for stuffing old waxy paper caps for when appearance is considered important. There are those who - particularly on pre-war sets - understandably find bright yellow polyester caps offensive to the eye. OK perhaps on a bog standard commonplace post-war set of no particular value or merit such as the DAC90A, but not a rare 1930s classic set which has been totally stripped and painstakingly rebuilt in a 'nut and bolt' wire by wire restoration.

[Stevie342000]

I am looking for a leakage tester for capacitors (self-build) the schematic and article mentioned someway up this thread (near the beginning) first seen in Popular Electronics October 1970 which can be found on American Broadcast History website (along with lots of other magazines - be warned you may be lost in there for days, sorry weeks).

I am assuming that the person who had the original magazine penciled in some modifications of another switch contact, resistor (which looks like 120 - 130R) and what looks like a 0.5mA fsd Meter (dc), as well as a single pole switch (what is the purpose of that switch?).  Looks like he has modified the unit to measure capacitor leakage.

Am I right in my assumptions?

Why do I want one, well I want to make sure that what I am putting in as so called new is not leaky?

Can this unit be used to determine in the leakage setting be used to determine what it is the inner and outer foil?

As on modern capacitors that is not marked and it does make a difference to hum levels if the capacitor is not connected the right way around.

[Crackle]

This is an electrolytic capacitor tester and reformer I made a little while ago.
http://www.forum.radios-tv.co.uk/viewtopic.php?f=15&t=3879&p=40688&hilit=capacitor+reform#p40688
It has found to be useful in reforming many electrolytics from post war radio sets. It is not always possible to reform all electrolytic capacitors, and I agree there is little point in attempting to reform pre war capacitors.

I also use it to make leakage tests on old film capacitors, it gives a reliable measure of leakage down to about 100uA. If the capacitor being tested is in a critical position like audio coupling, then I insert the AVO in series to get a more accurate reading.
The important factor is the tests are carried out at or near the working voltage of circuit the capacitor is used in.
I made a modification to the on / off swich, it was a double pole change over type and it also discharged the capacitor when switched back off.
Yes I did redo the scale.
The meter is not calibrated precisely but is probably about within 10% and that is all I needed.

Mike

[Stevie342000]

Thanks that helped, I suppose I could bolt the meter section of the item you provided details to and use the Popular Electronics circuit as that provides more voltage ranges than this one. I am looking at flexibility here and it is likely that I will not use the reformer part much if at all. Other than to check that any new electrolytics are good for service.

I have seen how to use them, often when you test a 400 volts Hunts capacitor or bumblebee type they are leaky even at 50 volts but well well below their working volts. The testers I have seen all use an electric eye tube in them which is very sensitive and form what I have read pretty indestructible compared to a meter. Now I wonder hmm.....oh well I could always wait for one to come up on line in auction.

But loathe to pay the prices that some of the CR Bridges and leakage testers go for, the Avo Bridge 1 (I think it is - the 1955 version) looks really good.

What is the best way to determine which is the inner and outer foil on modern capacitor (other than electrolytic)?

[Terry]

What is the best way to determine which is the inner and outer foil on modern capacitor (other than electrolytic)?

This is pure guesswork but, if it is important, why not try wrapping some tinfoil round the cap and then measure the capacitance between each connection and the foil?

If the difference in the readings is too small for certainty, try injecting a signal into the capacitor, then look for a signal between the foil and the earthy side of the source. Repeat with the capacitor connections reversed to see which way round produces the lowest level. 

I don't know if either of these will work but it is worth trying them as an experiment. 

[pwdrive]

https://www.youtube.com/watch?v=1f-LdpJiAk4

Lawrence.

[Stevie342000]

Thanks that works for me, so just connecting it across any input should give the same results, as I do not a guitar amplifier?

This was how I first came across this, I did know about from way back but had not given thought to polarity of non polarised capacitors:

https://www.youtube.com/watch?v=BnR_DLd1PDI

[pwdrive]

Yes, you can use a 'scope or an amplifier with a high impedance input.

Lawrence.