Help for Newbie on measuring capacitance

[Flux_Cap]

I need help with measuring capacitance on vintage paper in oil, paper in wax, or Mylar film capacitors. I am using these vintage capacitors on my guitars. There are many sellers on eBay that offer these. Guitars generally have a very low operational voltage values; we are talking millivolts at most over a frequency range which is probably the same as the frequency range for the human ear. Most of the eBay sellers that I get my capacitors from are using different types of meters then I use; such as the PEAK ESR 70 or some cheap capacitance or transistor meter they got on Amazon. These old capacitors usually drift up in capacitance with age. I recently ordered a couple .02 microfarad Sprague black beauties that the seller claims read at .025 on his 30$ capacitance meter. When I got them, they read .033 microfarads on my Fluke 115 True RMS mm on capacitance setting. I have checked other known good brand new caps with my Fluke and the measurements are spot on. So I am hoping someone can explain why there is a difference and which meter I should believe and how to avoid this problem in the future. Thanks in advance for any help clarifying this.

[stj]

Re: Help for Newbie on measuring capacitance

capacitance mat vary with frequency of the tester slightly.
you should be more concerned with ESR and leakage if your using them as signal filters.

[Flux_Cap]

Re: Help for Newbie on measuring capacitance

I thought leakage was only an issue at higher voltages. I don't see how leakage would be a problem. I really don't have a good understanding of ESR.

[stj]

Re: Help for Newbie on measuring capacitance

leakage is a problem if your trying to block dc from an amplifier.
esr is resistance at a specific frequency.
in audio filters lower esr = more signal getting through, often with a wider frequency range.
(better bass/top-end)

[Flux_Cap]

Re: Help for Newbie on measuring capacitance

leakage is a problem if your trying to block dc from an amplifier.
esr is resistance at a specific frequency.
in audio filters lower esr = more signal getting through, often with a wider frequency range.
(better bass/top-end)

ESR sounds like capacitive reactance Xc that I remember from my Navy electronics training. I have read many books on electric guitars and have never seen the term ESR when capacitor values are discussed. These ESR meters give the value of capacitance in farads not ohms. I would think that measuring a capacitor at a specific frequency would not be an effective way to test a capacitor that operates over a wide frequency range. Well, I appreciate your taking the time to respond. This does not seem.like an enticing topic for the rest of the forum. I'm not going to give until I understand this better. Perhaps I did not post this in the right forum topic.

[Flux_Cap]

Re: Help for Newbie on measuring capacitance

In my last post I meant to say that some ESR meters read capacitance in farads and some give a reading in ohms.

[stj]

Re: Help for Newbie on measuring capacitance

good ones give all 3 values.

pics later.

[CapLeaker]

Re: Help for Newbie on measuring capacitance

good LCR meters aren't cheap either... on the other hand... what is cheap these days?

[stj]

Re: Help for Newbie on measuring capacitance

component testers are 5-15 and work well, 99% of the magic is the software.

[Radio Fox]

Re: Help for Newbie on measuring capacitance

In my last post I meant to say that some ESR meters read capacitance in farads and some give a reading in ohms.

All ESR meters give a reading in Ohms (Equivalent Series Resistance). Some also give a capacitance reading.

[redwire]

Re: Help for Newbie on measuring capacitance

A leaky capacitor can fool some capacitance meters because it takes longer to charge up due to current loss in the dielectric.
So a leaky cap can read higher in capacitance on some equipment. Some days I get a different reading from every meter I own which drives me nuts.
Many capacitance meters are single-slope and only measure charge time to ramp up and calculate a value.

What you will find with old paper/wax caps is some leakage current supposedly due to the paper absorbing moisture.

ESR is not a useful measurement for low value film capacitors. These capacitors are too small in value and circuit impedances too high for it to matter. ESR is very important for wet capacitors, such as electrolytic capacitors.

Best to use a good DMM and check the dielectric insulation resistance through the megohms.
A perfect capacitor has no leakage current, but some is perfectly fine in a guitar as it is AC signal and would just soften the tone.

[Flux_Cap]

Re: Help for Newbie on measuring capacitance

component testers are 5-15 and work well, 99% of the magic is the software.

I think most of the ESR meters I've seen only test down to 0.1 microfarad. What is the best meter to use for these old and small (.015 to .047 )caps?

[Per Hansson]

Re: Help for Newbie on measuring capacitance

Flux_Cap, do you mean old caps like these?
https://www.patreon.com/posts/20834648

If so the component tester that stj recommended above is what I've used to measure those.
But also like redwire says it's likely that leaky caps can fool an ESR meter.
The little transistor tester is pretty smart though: it tests for leakage too!
If you look at the hand written text, within parenthesis that is what the meter read them as.
A value with a percentage is how leaky it was.
So for example the first cap, 100nF read as 330nF with 8% leakage and ESR of 3.3.
If you want I can test it with some DMM's too, and see what they say.
But all in all I have to question why not just replace these old crap capacitors?

[Flux_Cap]

Re: Help for Newbie on measuring capacitance

Flux_Cap, do you mean old caps like these?
https://www.patreon.com/posts/20834648

If so the component tester that stj recommended above is what I've used to measure those.
But also like redwire says it's likely that leaky caps can fool an ESR meter.
The little transistor tester is pretty smart though: it tests for leakage too!
If you look at the hand written text, within parenthesis that is what the meter read them as.
A value with a percentage is how leaky it was.
So for example the first cap, 100nF read as 330nF with 8% leakage and ESR of 3.3.
If you want I can test it with some DMM's too, and see what they say.
But all in all I have to question why not just replace these old crap capacitors?

Yes, these are similar to the caps Im interested in. I need to talk to Mr. Carlson too, thanks for posting that link. In the late 50's to early 60's, Gibson guitars used black beauty's, bumble bees and some paper and wax type caps, usually .02 microfarad. Guitar aficionados, luthiers building replicas, and hobbyists, like to try to use the same components used back in the 50's in order to chase that vintage tone. I totally agree with you. If you are restoring an old radio or amp or some other than a guitar, these old caps should be the first to go. For a guitar which sees only millivolts at most, Im not sure leakage would be a concern. A guitar tone circuit is just a frequency filter. The value of the cap changes the response curve which affects the tone. It would be nice to see how your DMM compared to that transistor tester though. I think Im going to have to buy anbokd vintage tester to test these old caps, I' don't know.

[Flux_Cap]

Re: Help for Newbie on measuring capacitance

Flux_Cap, do you mean old caps like these?
https://www.patreon.com/posts/20834648

If so the component tester that stj recommended above is what I've used to measure those.

Did I miss something? What tester did he recommend?

Thank you Redwire. I have been going nuts myself trying to buy these from sellers on eBay only to find out that they read way different on my Fluke 115. I've head to return several because they didn't read what the seller for using his meter. I'm not making friends on eBay this way!

[Per Hansson]

Re: Help for Newbie on measuring capacitance

The tester exists in a thousand variants.
If you want a recent one you should buy this one I link to here:
https://www.eevblog.com/forum/testge...31/#msg1730831
But the older meter exists in a cased variant, also shown there (which I also have, and like).

The first one I bought, it's this one (not recommending you buy it now, better variants exists today): https://www.ebay.com/itm/2016-EZM328...a/201663141755

Yes, these are similar to the caps Im interested in. I need to talk to Mr. Carlson too, thanks for posting that link. In the late 50's to early 60's, Gibson guitars used black beauty's, bumble bees and some paper and wax type caps, usually .02 microfarad. Guitar aficionados, luthiers building replicas, and hobbyists, like to try to use the same components used back in the 50's in order to chase that vintage tone.

This I'm sorry is called audiophoolery!
You seriously can't think that a 70 year old capacitor sounds the same today, with how much it has degraded, compared to how it sounded when it was new?

[stj]

Re: Help for Newbie on measuring capacitance

I think most of the ESR meters I've seen only test down to 0.1 microfarad. What is the best meter to use for these old and small (.015 to .047 )caps?

the new software can read fractions of a Picofarad afaik.

[redwire]

Re: Help for Newbie on measuring capacitance

I say be careful with Mr. Carlson and his capacitor leakage tester and his reasoning. Some of it is incorrect, from my point of view.

He seems to be confusing wet capacitor increased leakage current with that of failing film capacitors.
A few uA of leakage current at low test voltages and he says the film cap is bad.

Vintage capacitors have different dielectric absorption and ESL that seems to be the Holy Grail for old gear. Modern dielectric plastics in film caps are different (RoHs, SMT temperatures etc.) and do sound different depending on the circuit. Guitars are high-impedance so DA has a stronger effect.

[Per Hansson]

Re: Help for Newbie on measuring capacitance

It would be nice to see how your DMM compared to that transistor tester though.

Thanks for asking me to do this test: it was quite revealing:
My UNI-T UT61E reported pretty much spot on for all caps vs the "transistor tester"
With exception for the caps that the transistor tester showed a leakage percentage on:
Those it could not test properly: it would flash a value, then go back to zero, and flash a value, like it was getting overloaded (probably exactly what happens)

When tested on my useless Fluke 113 the resolution is only 1nF, so it can't show pF values.
It's behavior was different though: the first capacitor in my previous example that the transistor tester read as 330nF with 8% leakage and ESR of 3.3:
The Fluke 113 read that as 500nF, so it confirms the point made by others: cheap meters are fooled by leaky caps: they read them too high.
Well, maybe not cheap meters then, since I paid a grand total of $15 for my transistor tester kit back in 2016

I say be careful with Mr. Carlson and his capacitor leakage tester and his reasoning. Some of it is incorrect, from my point of view.

Agreed to some extent, but realize that he has allot of traditional high voltage capacitor leakage testers that he has compared it with.
But yes sure, some faults are bound to only be found with proper high voltage.

the new software can read fractions of a Picofarad afaik.

Indeed, it can go really really low.
It's discussed a bit here how to do it:
http://www.eevblog.com/forum/testgea...92/#msg1753292

[Radio Fox]

Re: Help for Newbie on measuring capacitance

...the first capacitor in my previous example that the transistor tester read as 330nF with 8% leakage and ESR of 3.3:
The Fluke 113 read that as 500nF, so it confirms the point made by others: cheap meters are fooled by leaky caps: they read them too high...

...and an expensive Fluke meter reads them even higher.