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 Post subject: Re: Is it OK to use NOS Electroltyic Capacitors ?
PostPosted: Apr Sun 05, 2020 2:20 pm 
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Location: Capon Bridge, WV
Then why does the liquid filled cap in my Philco still work? And no I didn't just plug it in and run it. This is the chassis I completely rebuilt/rewired after a total disassembly. That cap sat hooked up to my 950B for over 24 hours at 350V without even a hint of a problem. Its the one in the middle, on the tuner deck. That was a couple years ago and its still fine. Again, I only power this on once a month for a few minutes. Risky, I know :roll: but I see it as a testament to how some old caps do still work.

I can hear Leigh right now... "until they don't" :lol: .


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 Post subject: Re: Is it OK to use NOS Electroltyic Capacitors ?
PostPosted: Apr Sun 05, 2020 2:26 pm 
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Yes, SOME old caps are still good---all you have to do is figure out which ones.......

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 Post subject: Re: Is it OK to use NOS Electroltyic Capacitors ?
PostPosted: Apr Sun 05, 2020 4:39 pm 
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I can confirm Acornvalve's conclusions. Some old electrolytic capacitors are still good and it is possible to find 50 and 60 year old samples that have better specs in some regards than the ones you find today. Years ago manufacturers were concerned with low noise in analog circuits, which requires a low power supply impedance (= ultra low ESR) to control. They also optimized ripple current for 60/120 Hz and 50/100 Hz in keeping with linear power supplies which are now pretty much in the rear-view mirror. Today most electronic products are digital, with switching supplies, and low noise linear design is in the back seat. No capacitor manufacturer really gives a hoot about ultra low ESR or high ripple current at low frequencies these days as those are niche markets now. What's more, I have found that if a capacitor is within spec all three ways: DC leakage, AC loss (ESR, dissipation, power factor, or tan-delta) and capacitance, then there's no reason not to use it. Statistically it is less likely to fail than a new capacitor, and may in fact have better specs than anything you can find new.

Back in the late 1960s and early '70s, room temperature vulcanizing rubber and latex products were all the rage for sealing and potting things. What was not realized initially is that those products contained acetic acid which would outgas and prove highly corrosive to surrounding metals. I've seen some which tested completely open because the terminals were still attached to the phenolic disks, but had completely corroded away behind the disks. Also some which developed leakage from one section to another through the latex behind the phenolic. The materials were also subject to eventual shrinkage and cracking, so it is not a surprise that capacitors made with them are found hopelessly dried out today. Electronic grade potting and sealing compounds free of acetic acid, with controlled shrinkage have been developed since, but some "bad 'uns" got into the field before people realized what was going on. On the other hand, capacitors made with good neoprene rubber seals seem to have held up a lot better.

Paper capacitors are much trickier and far less likely to be salvageable, but some are. I've been studying the subject and have tentatively concluded that the problem is that most of the capacitor paper used from the 1930s through the 1960s was impregnated with oil or paraffin wax before the capacitors were wound and cased. These "filler" materials were used to fill voids in the paper fibers and to increase the dielectric constant. They may have also served a mechanical purpose, ensuring a tighter, more uniform wind and better running machinery! Unfortunately, most types of oils oxidize and break down over time, releasing water molecules and losing their dielectric properties, and then there is no going back from there.

The key to understanding it is that the old filter packs in 1920s radios are often still perfectly okay nearly a hundred years after they were made, as are some of the other large paper capacitors from that era. Disassembling some of them has revealed that the paper was apparently not impregnated with oil or wax, or they used beeswax in some cases. Also, Solar Sealdtite capacitors from the early 1940s are often still good today. It appears possible they used a very early form of silicone oil which does not break down like ordinary mineral or petroleum oils.

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Last edited by Chris108 on Apr Sun 05, 2020 5:10 pm, 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 4:43 pm 
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pixellany wrote:
Yes, SOME old caps are still good---all you have to do is figure out which ones.......

or we could allow the transformer, field coil, and rectifier decide.

(just being silly)

steve

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 Post subject: Re: Is it OK to use NOS Electroltyic Capacitors ?
PostPosted: Apr Sun 05, 2020 4:57 pm 
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Hello ACORNVALVE,
nice job on that cap you stuffed and I also will use small machine screws for connects .
Yes John I a with you far repairing I would never use a nos electrolytic cap I used other parts thou and tested them before use.

Sincerely Ric
P.S. like the older philco and zenith sets from the 30s to 50s I find they have dried out as a cause of the seals .


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 Post subject: Re: Is it OK to use NOS Electroltyic Capacitors ?
PostPosted: Apr Sun 05, 2020 5:32 pm 
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ACORNVALVE wrote:
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...
IMHO that is a lot of labor and pricey tooling to accomplish what a bit cost that new builds of these caps can be purchased for. I often leave the can in place, disconnected, populate with caps under the deck. Or, Hayseed it. Could it be that simple? Yes :D Will I charge just as much for the repair, Yes! Will it be just as easy for the tech in 2030 or 2040? Yes, but that tech may have a hard time finding the parts :roll:

YMMV

Chas

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 Post subject: Re: Is it OK to use NOS Electroltyic Capacitors ?
PostPosted: Apr Sun 05, 2020 7:35 pm 
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:) The resurfacing of this discussion reminds me of YouTube videos of the guy opening up old army field rations/MRE's. He would find some decades old field rations that's still (sort of) edible, but that doesn't mean all/most of them are still good.

Why take a chance with a 50-year old can of beans when I can buy a new one at the store, cheap.


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 Post subject: Re: Is it OK to use NOS Electroltyic Capacitors ?
PostPosted: Apr Sun 05, 2020 9:35 pm 
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Because thats the answer for everything these days. Its old? Throw it out and buy a new one :lol: :wink: . Just being silly. I know caps go bad and get tossed.

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 Post subject: Re: Is it OK to use NOS Electroltyic Capacitors ?
PostPosted: Apr Sun 05, 2020 10:19 pm 
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UV201 wrote:
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.
R/ John

John,

I have at least 10 TM 500 style Tek mainframes, most are TM501's amd TM503's.

In all but one unit, the capacitors in the power supplies are still perfect.

It was one NOS TM501, never used, which contained the Sprague capacitors, which were open circuit due to the internal latex corrosion. Oddly, none of the other TM units I have, use the Sprague, they are a different brands, none have failed.

I'm pretty confident that its only the Spragues that have the latex in them, but not 100% sure. That is why it would be good for others to open up defunct caps to look. It this is case, the sprague twists locks from this era should be replaced on sight I think.

So we are looking at sprague twist lock caps that go open circuit, with no use at all, NOS. So I have seen this in the NOS dual 100uF units on the post and in the TM501 mainframe now, both sprague . But the ones in the main frame had corroded through internal terminals, and the dual 100uF ones simply dried out, but they still had internal latex related corrosion.


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 Post subject: Re: Is it OK to use NOS Electroltyic Capacitors ?
PostPosted: Apr Mon 06, 2020 12:40 am 
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Interesting, and my experiences with my TM503 and TM504 are the same ... original electrolytics that are good. I don't actually use them all that much, but I faithfully power them up for a while every month (including installing all the various plug-ins I have, and running them through their paces).
R/ John


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 Post subject: Re: Is it OK to use NOS Electroltyic Capacitors ?
PostPosted: Apr Mon 06, 2020 2:14 am 
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Quote:
it is possible to find 50 and 60 year old samples that have better specs in some regards than the ones you find today. Years ago manufacturers were concerned with low noise in analog circuits, which requires a low power supply impedance (= ultra low ESR) to control.

The old capacitors are considerably larger than modern ones. They had thicker foil so less resistance.

The capacitance tolerance on old capacitors is looser than on new ones and when measured are frequently much higher capacitance than the marked value.

Both of these "features" would give better performance than newer capacitors in line operated power supplies.

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 Post subject: Re: Is it OK to use NOS Electroltyic Capacitors ?
PostPosted: Apr Mon 06, 2020 2:48 am 
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UV201 wrote:
Interesting, and my experiences with my TM503 and TM504 are the same ... original electrolytics that are good. I don't actually use them all that much, but I faithfully power them up for a while every month (including installing all the various plug-ins I have, and running them through their paces).
R/ John


John,

Here is the story about the open caps in the Tek power unit:

http://worldphaco.com/uploads/ELECTROLY ... FRAMES.pdf

I also added some notes about "self cracking resistors" found in a Telequipment scope.These were tricky and left g1 grids floating.

I think it is good idea, when we can, to try at least to figure why the components we replace have failed. One electro for example that had shorted out, I opened it up and unwound the foils and found a metallic fragment in the insulation that shorted the foils. So that was a manufacturing issue, just for that particular one perhaps or maybe the factory conditions were not as clean as they should have been.

There are a lot of components, such as epoxy cased semiconductors where it can be difficult to work out why the junction failed, while device was supposedly operating within its ratings.

I think with electros though, its worth trying to work out what happened, then it helps in the assessment of other similar ones as to what might likely be happening. With the rush of the modern world & time constraints, most defective parts are not investigated and go straight in the bin, but the technicians remain none the wiser as a result and lack a data base of the events that are taking out the components.


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 Post subject: Re: Is it OK to use NOS Electroltyic Capacitors ?
PostPosted: Apr Mon 06, 2020 4:10 am 
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Location: Phoenix, AZ
I also enjoy forensics of that sort ... trying to figure out and understand the "why's" of the failure mechanism is interesting.

A bit off-topic regarding capacitors, but a bit of useful trivia in reference to the Tektronix TM mainframes:
A few years ago I obtained a DC5009 counter plug-in from a surplus store for a very good price. All I have are TM500-series mainframes, and I wanted to use the counter. People say that one cannot use a 5000-series plug-in in a TM500-series mainframe, and they're right because the GPIB interface edge connector on the rear of a 5000-series plug-in collides with the sheet metal at the back wall in the TM-500 series mainframe cavity. I thought "I want to try this anyway," so I disassembled my TM504 mainframe and milled a small slot in the correct location to clear the unused edge connector. Presto, it fits, the unused edge connector does not extend too far back (e.g., it does not physically reach or short to the mainframe power supply board), and the DC5009 counter works perfectly ... I just don't have the GPIB interface.

Sorry for the tangent ... now back to our regularly-scheduled debate about capacitors.
R/ John


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 Post subject: Re: Is it OK to use NOS Electroltyic Capacitors ?
PostPosted: Apr Mon 06, 2020 5:50 pm 
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I will not use new old stock capacitors as it just is not worth the risk IMO. If I was to use NOS capacitors I would install a B+ fuse in-between the rectifier and first capacitor. Interesting that I never ran into a shorted electrolytic capacitor in the 50 years I have been playing with tube gear. I have found loss of capacitance though with large amounts of AC hum on the audio.


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 Post subject: Re: Is it OK to use NOS Electroltyic Capacitors ?
PostPosted: Apr Mon 06, 2020 8:16 pm 
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jimbenedict wrote:
Interesting that I never ran into a shorted electrolytic capacitor in the 50 years I have been playing with tube gear.

It is not haw many years you have been playing with tube gear, but the thousands of units you have repaired that makes a difference. Yes, electrolytics do develop excessive (shorts) and self distruct usually taking rectifier tubes and transformers with them.

DM


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 Post subject: Re: Is it OK to use NOS Electroltyic Capacitors ?
PostPosted: Apr Mon 06, 2020 9:33 pm 
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badwaxcaps wrote:
Then why does the liquid filled cap in my Philco still work? And no I didn't just plug it in and run it. This is the chassis I completely rebuilt/rewired after a total disassembly. That cap sat hooked up to my 950B for over 24 hours at 350V without even a hint of a problem. Its the one in the middle, on the tuner deck. That was a couple years ago and its still fine. Again, I only power this on once a month for a few minutes. Risky, I know :roll: but I see it as a testament to how some old caps do still work.

Uh huh...And then hold your breath in hopes nothing happens? ALL of my tube radios, and most of my Transistor sets, have had their caps replaced. Consequently, I don't have to hold my breath when operating them... :wink:

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 Post subject: Re: Is it OK to use NOS Electroltyic Capacitors ?
PostPosted: Apr Mon 06, 2020 10:08 pm 
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I too have opened up many old electrolytic capacitors that tested bad. The most common thing I found is that the electrolyte had dried up. I did find one once that had a low constant resistance, though I did not open it to find out why.
I acquired a large stock of NOS electrolytics (old stock from the 60's through 80's) about 20 years ago. I have yet to find one that has low resistance, but I have found a few that show capacitance slightly below, or slightly above, their rating. Never found one that had abnormally low capacitance.
Before using any of those, I inspect them for leaks. Then, I apply a DC voltage, through a 10K resistor, (for lower values, I switch to a larger resistance), that is equal to the voltage that it will have applied to it in the circuit, and watch the voltage rise on my voltmeter. That is supposed to "form" the capacitor. Then, I allow the capacitor to discharge through the same resistor. I apply the same voltage again through the same resistance and watch the voltmeter. The time can be measured for both charge and discharge, and the forming charge time and post-forming charge time can be compared. For more accuracy, larger values resistor can be used, but the charge/discharge times increase.
Surprisingly, not very often is there a big difference between the two charge times. When there is, I repeat the test a third time and if there is no change from the second test, I call it good.
So far, only one of those NOS electrolytics have failed the test. I mostly use them to repair jukebox amplifiers from the about 1940 and up. Here is a Wurlitzer 501 amplifier that has two of them installed, and a few shown in the next picture as samples.


Attachments:
Wurlitzer503amp.jpg
Wurlitzer503amp.jpg [ 191.91 KiB | Viewed 202 times ]
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Electrolytics.jpg [ 203.02 KiB | Viewed 202 times ]


Last edited by startgroove on Apr Tue 07, 2020 1:02 am, edited 4 times in total.
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 Post subject: Re: Is it OK to use NOS Electroltyic Capacitors ?
PostPosted: Apr Mon 06, 2020 10:15 pm 
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Shelf life

https://passive-components.eu/get-the-l ... apacitors/

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 Post subject: Re: Is it OK to use NOS Electroltyic Capacitors ?
PostPosted: Apr Tue 07, 2020 2:36 am 
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There are a lot of components, such as epoxy cased semiconductors where it can be difficult to work out why the junction failed, while device was supposedly operating within its ratings.

I have heard, but have no way to confirm, that failure of early epoxy-cased semiconductors was caused by the epoxy having a different thermal coefficient of expansion from the silicon. This resulted in the bond wires being pulled off the chip with normal temperature cycling. The ones I have seen that I think have this problem have been intermittent. In a certain range of temperature, the wire touches the chip and the device works. At other temperatures, the wire lifts and it doesn't work. Devices made since the late '60s or early '70s have a blob of elastomeric substance over the chip to cushion the stresses.

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 Post subject: Re: Is it OK to use NOS Electroltyic Capacitors ?
PostPosted: Apr Tue 07, 2020 4:32 am 
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Pbpix wrote:

Quote:
Conclusion
For most capacitors, the shelf life is significantly determined by storage conditions.

So that really tells us little. The storage conditions in your climate are going to be different than in mine, and in either climate we still don't know the longevity.

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