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 Post subject: Is it OK to use NOS Electroltyic Capacitors ?
PostPosted: Apr Sun 05, 2020 12:58 am 
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Joined: Jan Thu 16, 2020 12:29 am
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This question will have come up before. Since I am in the process of re-building some FP style twist lock types, I thought I would share some experiences that shed some light on this question.

In the attached photo, right hand side, the is an NOS dual section 100uF + 100 uF 50V Sprague type (that I bought as donors for their housings). They are interesting in that:

1) The date code suggests 1975.
2) The capacity reads 3uF per section.
3) The ESR is so high its off the scale of my meter (Reads open on the ESR meter)
4) Inside the capacitor is totally dried out, the paper is like parchment paper.
5) There is latex rubber there as a space filler between the capacitor body and the top of the inside of the aluminium canister. Where the latex has melted on the the aluminium, there is severe corrosion.

So despite being NOS the capacitor is useless.

On the right hand side is an NOS capacitor , Aerovox type 30uF 450V, I bought on ebay and fitted experimentally to a radio. It is interesting in that:

1) its capacitance reads 33uF on the meter
2) the ESR reads 0.9 Ohms, a modern 33uF 450V cap in my stock read 1 Ohm.
3) The leakage current in operation settles on 0.1mA with 250V applied. For the modern cap it settles on 0.05mA.
4) This capcitor used a different narrow seal system to the sprague (which has a wider phenolic/rubber phenolic seal.
5) It is not known by me currently if this brand contains the latex rubber or not, probably it doesn't.
6) The date code/s suggests early 1960's.

So what can be concluded from this, a number of things I think.

Firstly the Aerovox capacitor that is 15 years older than the Sprague, still, from all exterior tests, appears perfectly normal electrically. It cannot have dried out or the capacity would have dropped and the ESR elevated. It must have a much better seal at the base.

So the answer about NOS electrolytic caps I think comes down to the design & construction of the original capacitor, how good the seals were at keeping in the water and its vapour and likely whether it is a type that contains latex rubber or not.

I have attached a photo showing the latex rubber damage inside other sprague capacitors of 1970's vintage. It was interesting that these ones had not dried out, they went O/C because the interconnects were corroded through by melted latex.


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aero.jpg
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 Post subject: Re: Is it OK to use NOS Electroltyic Capacitors ?
PostPosted: Apr Sun 05, 2020 1:09 am 
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Location: Near Brandon, Iowa
I think that your sample size is too small to justify drawing any conclusions.


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 Post subject: Re: Is it OK to use NOS Electroltyic Capacitors ?
PostPosted: Apr Sun 05, 2020 1:28 am 
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I regularly reuse old electrolytics (including ones salvaged from CFLs) PROVIDED that they test good on my Eico 950B, including having low power factor and I reform them. I haven't had any problems with them.

In one ongoing project, I used 2 electrolytics, one of which had a paper label taped on saying that it had been reformed in 1956. I also tried two modern capacitors in their place. The old ones gave lower ripple.

I also have many bad electrolytics, both old and newer.

I don't do repairs or sell to others so I am willing to take the risk. So far, nothing bad has happened.

Paper capacitors are another matter; they are ALWAYS bad.

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 Post subject: Re: Is it OK to use NOS Electroltyic Capacitors ?
PostPosted: Apr Sun 05, 2020 1:32 am 
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Location: Capon Bridge, WV
With hundreds and hundreds of millions of capacitors out there it stands to reason that some vintage units will work and others will not. I have a Philco cathedral that still has an original liquid filled electrolytic in place and functioning. I've always chalked it up to luck of the draw. Kudos to you for your investigation :D .

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Last edited by badwaxcaps on Apr Sun 05, 2020 3:11 am, edited 1 time in total.

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 Post subject: Re: Is it OK to use NOS Electroltyic Capacitors ?
PostPosted: Apr Sun 05, 2020 1:38 am 
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Location: Fulton missouri
What about storage conditions? If one was in a controlled environment and the other stored in an attic that had extreme heat and cold wouldn’t that make a difference?


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 Post subject: Re: Is it OK to use NOS Electroltyic Capacitors ?
PostPosted: Apr Sun 05, 2020 1:54 am 
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lorenz200w wrote:
I think that your sample size is too small to justify drawing any conclusions.


I a sense agree with that remark, about these particular ones, however, given that I have seen latex cause this exact same problem, not only in capacitors, but vintage radio vibrators, I think it is very likely that observation is solid. Also, I have opened up many types of electrolytics over the years, invariably the ones that have lost their capacity have dried out. So these ones on the post are just current examples of what I'm working with right now and they do represent what I have seen many times before, so its not really a cross sectional study, of just these few parts, its a retrospective, with many cases of these dilemmas seen before.


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 Post subject: Re: Is it OK to use NOS Electroltyic Capacitors ?
PostPosted: Apr Sun 05, 2020 1:55 am 
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no

steve

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 Post subject: Re: Is it OK to use NOS Electroltyic Capacitors ?
PostPosted: Apr Sun 05, 2020 2:02 am 
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Clint wrote:
What about storage conditions? If one was in a controlled environment and the other stored in an attic that had extreme heat and cold wouldn’t that make a difference?


I think the storage would make a big difference, especially temperature & humidity, especially if the seals at the base or ends of the capacitor were not perfect. Likely the rubber there degrades over time and may become porous.

As an experiment I dropped a dried out capacitor (that I had removed from its canister) into a glass of de-ionised water. By the following day, its uF value and ESR had returned to normal. So It was a case that over 40 years, the H20 had "left the building". Yet looking at the capacitor (which was an axial type) the seal looked normal at the end, the rubber looked normal and there was no evidence of leaked electrolyte, the rubber was not conductive either. So the leak was small enough over the years, just to let H20 molecules leave. One interesting thing, (I did not formally weigh it) the capacitor felt very light in the palm of the hand.


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 Post subject: Re: Is it OK to use NOS Electroltyic Capacitors ?
PostPosted: Apr Sun 05, 2020 2:06 am 
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badwaxcaps wrote:
With hundreds and hundreds of millions of capacitors out there it stands to reason that some vintage units will work and others will not. I have a Philco tombstone that still has an original liquid filled electrolytic in place and functioning. I've always chalked it up to luck of the draw. Kudos to you for your investigation :D .


I've always thought those capacitors should be intrinsically reliable, that is if they are not let down by the natural rubber seals around the pin that exists through the threaded base. It makes one wonder if the seal material was better, something like Silicone Rubber, they might have lasted a hundred years or more.


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 Post subject: Re: Is it OK to use NOS Electroltyic Capacitors ?
PostPosted: Apr Sun 05, 2020 2:11 am 
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i have a big box full of nos sprague twist lock lytics. they are 1980s era.

i use them to stuff the chassis hole if the original can is missing. (individual new capacitors under the hood)

that is all they are good for in my book. they are not worth a power transformer and/or rectifier tubes.

let the pizzing contest begin...

steve

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 Post subject: Re: Is it OK to use NOS Electroltyic Capacitors ?
PostPosted: Apr Sun 05, 2020 2:15 am 
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Jim Mueller wrote:
I don't do repairs or sell to others so I am willing to take the risk. So far, nothing bad has happened.

Paper capacitors are another matter; they are ALWAYS bad.


I agree.

If its your own gear you can assess the component yourself, for your own use. If you are repairing/selling gear its another matter and a NOS capacitor should never be used in my view, as you don't really know what is going on inside them until you open them up, and it can be a disaster in there. The external tests are merely an estimate of the internal condition.

It might be possible to detect the presense of or see the effects of Latex related corrosion on X-ray, I have not attempted this.

What I'm interested in though is to find out if Sprague was the only company to use latex in their electrolytics, I have not found it yet in any other brand, but since I had been replacing twist locks with NNS types from AES, I'm less familiar with them compared to other chassis mount or axial electros.

So the questions that others might answer could be:

1) has anyone seen latex inside any other electrolytic brand, if so which ones.
2) Does anybody know if the new twist lock caps being manufactured contain latex ?

When electros fail, most technicians just throw them in the bin, I have always opened them up for inspection to find out what went wrong.


Last edited by ACORNVALVE on Apr Sun 05, 2020 2:24 am, edited 1 time in total.

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 Post subject: Re: Is it OK to use NOS Electroltyic Capacitors ?
PostPosted: Apr Sun 05, 2020 2:22 am 
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Dutch Rabbit wrote:
i have a big box full of nos sprague twist lock lytics. they are 1980s era.

steve


Steve,

Are you willing to to check 3 or 4 types or as many as you have different brands and check if they contain the latex rubber. If it is there it is just under the top of the canister, so you could cut parts of the top off with some sharp cutters. That is if you are prepared to sacrifice any that you have.


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 Post subject: Re: Is it OK to use NOS Electroltyic Capacitors ?
PostPosted: Apr Sun 05, 2020 2:44 am 
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my shop is two counties over.

i am not planning to go there for a while...

also, i paid some money years ago to have these on hand for chassis hole stuffers, so i don't want to ruin any.

steve

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Last edited by Dutch Rabbit on Apr Sun 05, 2020 3:55 am, edited 1 time in total.

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 Post subject: Re: Is it OK to use NOS Electroltyic Capacitors ?
PostPosted: Apr Sun 05, 2020 2:51 am 
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nope, did that once with a 30 yr old NOS can. "Reformed and checked", pretty cheap, worth a try, played about 12 hours nicely, then the hum started to grow louder...

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 Post subject: Re: Is it OK to use NOS Electroltyic Capacitors ?
PostPosted: Apr Sun 05, 2020 3:10 am 
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I'd like to add that that Philco 'lytic isn't in daily use. I power it (37-60) up maybe once a month. Not even a smidge of hum.

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 Post subject: Re: Is it OK to use NOS Electroltyic Capacitors ?
PostPosted: Apr Sun 05, 2020 3:52 am 
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With any old capacitor, you are taking your chances. As most old radios and early TV sets did not have AC line fuses, a shorted capacitor could be disastrous. That said, the later low voltage caps do seem to hold up better.

Much depends on the quality and type of materials used in the original construction.

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 Post subject: Re: Is it OK to use NOS Electroltyic Capacitors ?
PostPosted: Apr Sun 05, 2020 8:31 am 
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Tim Tress wrote:

Much depends on the quality and type of materials used in the original construction.


That seems to be my experience with them too. I have attached a photo of a very large sized cap I re-built for a Bush TV22 TV set. Because these are AC/DC sets, there was no escaping rebuilding it. For this one I made a screw & nut terminal arrangement and left the original canister largely intact. I do not believe in sawing through their wall as some do for re-builds.


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 Post subject: Re: Is it OK to use NOS Electroltyic Capacitors ?
PostPosted: Apr Sun 05, 2020 9:32 am 
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This is an interesting investigation, but I think a larger sample size would be appropriate before solid conclusions can be drawn. I will admit that (for personal projects only) I sometimes have reused HV electrolytics I've salvaged from a few 500-series tube type Tektronix scopes (note, these scopes had already been partly scrapped by someone else, sort of a sad story by itself, and the remains then were given to me for whatever else I could glean). All of those electrolytics (so far) have reformed with ease and exhibit very low ESR; no question, Tek used high quality parts. I also have tested NOS Sprague and Mallory "replacement-grade" electrolytics I've accumulated over the years, unused and many still in their original boxes from the 1960s/1970s; these are rated 300 WVDC and higher, and fully 2/3 of them have refused to reform and have had high ESRs. My experience with old electrolytics having ratings lower than about 200 WVDC is that they are almost always bad, and I now don't even bother to test them. I do save the electrolytics from Tek scopes, and I also save a selection of old (bad) caps for restuffing when the package size is uniquely right for a restoration and above-chassis cosmetics matter.
R/ John


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 Post subject: Re: Is it OK to use NOS Electroltyic Capacitors ?
PostPosted: Apr Sun 05, 2020 11:38 am 
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Sample Size:
With well over 100 restorations in the last 10 years, I'm not sure that I have proved anything.

Here are some pretty much unrelated data points:

1. My 70s Tek scope is still running on the original electrolytics. In my simple brain, that proves exactly nothing.

2. In some '70s "popular-priced" stereos, there were enough bad electrolytics to motivate me to replace them all. That proves that some '70s popular priced stereos might need some new electrolytics.

3. In over a hundred "plain old radios", I've just shotgunned the electrolytics. Almost all the replacements were Miec brand from JustRadios. To my knowledge, none have failed.
While it's tempting to conclude something from this, people who make their living from understanding statistics might say I've just been lucky......

A practical observation that applies to many situations, including the work I do for customers:
Parts are cheap.

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"Even if you don't understand Ohm's Law, you are still required to obey it."


Last edited by pixellany on Apr Sun 05, 2020 1:04 pm, edited 2 times in total.

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 Post subject: Re: Is it OK to use NOS Electroltyic Capacitors ?
PostPosted: Apr Sun 05, 2020 1:01 pm 
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pixellany wrote:
Parts are cheap.


A big DITTO

I am well past 3,000 restorations over the last 35 years. Consider the "COSTS" of one return under one year warranty.
$50 or so shipping two ways = $100.
My time to walk customer through how to get the chassis out and how to pack it for safe shipping. My time to fix the problem. Aggravation of customer for having to take it apart ship it unpack and reinstall it into the cabinet. Price is beyond calculation. I have been known to warranty a couple that had been out there for close to twenty years because when I found the problem I felt that I should have replaced that part the first time around.

vs Parts cost for a few more parts. Way less than ZERO COST

The only Good Sounds are Any Old Capacitor hitting the bottom of the trash can.
John k9uwa

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