Restoration Commences on 1947 RCA Victor 721TCS

[Yamamaya42]

Originally Posted by bandersen

Here's what I found when I unrolled a cap from an RCA 630TS. Rotting aluminum and pinholes through the insulating layer. I've restuffed quite a few and often they look like this or worse.

what cap #is that in the RCA 630TS, if I may ask?

[Penthode]

Originally Posted by bandersen

Here's what I found when I unrolled a cap from an RCA 630TS. Rotting aluminum and pinholes through the insulating layer.

Interesting and I have seen the same. Notice the foil is very thin and exposing the corroded outer layer you tore the foil.

My question is that if only on the outer exposed foil, the thin aluminum foil has degraded, how about inside? And why how would the minor corrosion materially affect operation if the dielectric maintains low leakage and the capacity remains unaffected?

I disconnected the input filter from the 721TS to measure leakage and capacity this morning. This is after "patient"reforming after the 73 year old capacitor which had not been used for 60 years. The leakage had actually dropped in the 45 hours use from 500uA to 100uA at 400v for the 80uF capacitor. At the high line voltage around here (123vac) the input voltage across this capacitor runs at about 330VDC. The rule of thumb absolute maximum leakage from two sources online suggest 1mA leakage for every 50uf for a 450v capacitor.

One thing I noticed is that the 60 Hz Power Factor is not as good as a new capacitor.

Anyhow here are some meter readings from this morning. The Sprague meter is on the 0.6mA full scale range and reads 0.1mA at the 400v on the VTVM.

Meanwhile try opening up that 630TS capacitor to see if the corrosion permeated the internals. Somehow I don't think it did. Otherwise, the capacitance would have been noticeably reduced.

[Electronic M]

Originally Posted by Penthode

That suggests another study which is to reform an old capacitor and then take it apart to analyse it. I still do not understand your reasoning that if the capacitor fuctio n's within original s specifications how it could function at all with pinholes? How can you be sure that unless you disassemble a new capacitor, it doesn't haved pinholes as well?

I've disassembled New and old capacitors. New ones do NOT have pinholes or rot like bandersons picture illustrates.

I have seen plenty of old caps like bandersons picture that were rotten inside the foil roll.

[Electronic M]

Originally Posted by Eric H

Cool, I've never even put 50 hours on any of my old sets.

Closest thing would be a cheap 19" RCA from 1970 that I have been using the last couple months to watch old shows on DVD.
Recapped the films but not the Filter, got a dozen or so hours so far but the rejuvenated CRT is likely to die before the caps do.

Some of my color sets get that much use in a week some weeks. And those sets usually get around that much run time in a month.

My monochrome sets usually see fewer hours.

[Penthode]

Originally Posted by Electronic M

I have seen plenty of old caps like bandersons picture that were rotten inside the foil roll.

So tell me how that materially affect the operation of the capacitor? I am sure you know if you live in the north, your car can still show rust and still be fully operational.

My point is that you are not scientifically assessing the damage and whether it impairs the operation of the capacitor. I am now inclined to take an old capacitor (I have a parts 630TS with rusty chassis) send it through my reform school, confirm it first measures okay then dismantle it to have a closer examination.

[bandersen]

Here's another from the 630TS. Different cap much deeper into the roll.

These caps showed as shorted in my vintage Solar tester.

I routinely test caps before opening them up. Ones that showed shorts or excessive leakage that would not reform often look like this.

I've had many that showed little leakage, but also very little capacitance. Gone open in other words. I see this more often than shorts.

[Yamamaya42]

Originally Posted by bandersen

Here's another from the 630TS. Different cap much deeper into the roll.

These caps showed as shorted in my vintage Solar tester.

I routinely test caps before opening them up. Ones that showed shorts or excessive leakage that would not reform often look like this.

I've had many that showed little leakage, but also very little capacitance. Gone open in other words. I see this more often than shorts.

By the look of it, it seems to be c224 RCA (C5 SAMS) or c220 RCA(c1 SAMS).

[Penthode]

Okay, unwrapping a shorted capacitor or one that had failed I would expect the appearance you depicted! My point is if the capacitor reforms with low leakage and an even lower leakage is observed after 100 hours, the capacitor should have no problem in service for 1000 hours.

Again I am inclined to open a good capacitor of this vintage and not one that has failed. The key is that the leakage remains low over time.

And do you honestly intend to run your sets hundreds of hours?

[Electronic M]

Originally Posted by Penthode

And do you honestly intend to run your sets hundreds of hours?

Some of us do. I have a couple of color sets that I've used 3-50 hours a week every week for 6-8 years.

[Yamamaya42]

I really fail to see what the point of all this discussion / contention is all about.
When it has been shown over and over again, (and there are many sites dedicated to this. ) that in the restoration of vintage electronics, decades old capacitors, electrolytic and paper, are inherently unreliable due to entropic degradation, and even though they may seem to work, they are like a time bomb waiting to go off, and best replaced with more modern ones which are smaller, and often will preform better and last longer than what is being replaced, especially if high tolerance long life type is used, and of slightly higher voltage range than the original.
And, as it has been pointed out more than once, these new caps can be stuffed into cans of the old, leaving the visual aesthetics unaffected, or, as in the case of my CTC-16XL, I just unhooked the old caps on the bottom, and placed the new ones various places under the chassis, from the top, you can't tell anything was replaced, and I chose the new caps very carefully, all high tolerance long life, if replacing 80uf @ 450v, I put in a 500v one, 20uf @ 250v = 300v , and so on.

It's MY choice not to risk things on old caps, and I'm sure others feel the same, but if you want to run your stuff with them, go right ahead!

[init4fun]

I think the bottom line here is this ;

old capacitors are kinda like old people , some live a perfectly healthy life well into their 90s and some begin to seriously degrade starting in their 60s and don't make 70 . And when those people were young there really was no telling which would see the near century mark VS who'd be worm food by 60 . I'm sure there are those caps that'll live to a ripe old age performing their capacitor duties just fine without missing a beat just as there are plenty of them that are right now going to crap in 5 year old TVs , all the while their antique counterparts are still happily doing the cap thing without a whimper . It's luck of the draw , nothing more , and while I think it's great that those particular caps reformed well and came back to life I don't believe every , or maybe even every other , antique cap can be revived in such manner . As a cool experiment I think it's great that you had success but with the destructive nature of a shorted Ecap in mind I do systematically replace every one in any "daily driver" sets I run , just so that I can feel somewhat comfortable leaving them to run while I do things in other parts of the house without having to keep a literal eye on them

I , for one , am hoping to see your experiment run well into the hundreds of hours .....

[Penthode]

Originally Posted by Yamamaya42

I really fail to see what the point of all this discussion / contention is all about.
When it has been shown over and over again, (and there are many sites dedicated to this. ) that in the restoration of vintage electronics, decades old capacitors, electrolytic and paper, are inherently unreliable due to entropic degradation..


It's MY choice not to risk things on old caps, and I'm sure others feel the same, but if you want to run your stuff with them, go right ahead!

Entropic degradation? I am curious what this is.

I am amused bt your comment "when it is shown over and over again". There is a lot of stuff on the internet by many self proclaimed experts. You have not attempted to test the process and I see you are not willing to accept the evidence I has provided. The set has been on now continuously for over six hours reaching a total of 50 hours and the electrolytic capacitors remain fine.

I am not disputing anyone who chooses to replace the electrolytics. However I am disconcerted by reading here that all capacitors including electrolytic, paper and mica should be blindly replaced.

It is amusing to see defensive reaction to my hobby specific activities. I do not disagree with you if yo prefer to replace the capacitors. I have refilled many electrolytic cans myself, most recently my HP DC power supply. I am only posting this information here to demonstrate to all how the capacitors can survive more than seven decades and still work.

I am going to look inside a reformed good capacitor to see what degradation has occurred. I would also suggest you try reforming an old capacitor properly and then testing it for yourself.

I abhor the practise of applying power or even use of a Variac on a set that has not been thoroughly vetted and corrected. It is fraught with danger and because these electronic devices rely upon oscillators to generated grid bias, will lead to other component failures.

Note in this case, I reformed the capacitors and made all the required component replacements after detailed analysis of the circuit before applying full power. This set came up immediately and worked without issues.

[JohnCT]

Originally Posted by Penthode

I would also suggest you try reforming an old capacitor properly and then testing it for yourself.

I think you're assuming members of this forum haven't tried this. I won't speak for any other old timer here, but I have tried it as I mentioned in an earlier comment. What I discovered was that it was hit or miss, and therefore a waste of time when your name goes on a repair. Your example, although very interesting, won't change my experiences.

The Andrea I'm working on has a lot more hours than yours (I'd guess it's well over a hundred twenty five hours since February) and 5 of the cans are still good and operating fine, but history tells me that they're on bonus time. Using my own TV as an example, two cans were dead immediately, and two failed some 20-30 plus hours after it was running perfectly. The remaining 5 are still running fine at over a hundred hours. They're still coming out.

Sure, you can have capacitors work after 70 or more years, but proving a capacitor can work at 70 years and proving a capacitor can work for 15 hours a week for the next 10 years is another thing entirely.

I mentioned earlier that I'm restoring an 1850s reed organ melodeon. The leather exhauster is still working, but if don't replace the leather, how long will my wife be able to play the melodeon before the leather tears? 10 hours, 100 hours? Maybe she'll never put enough hours on it, but I'm replacing the leather anyway. Once this melodeon is finished, I don't want to ever take it apart again.

That's the point we're trying to make on this subject.

John

[Electronic M]

Originally Posted by JohnCT

I think you're assuming members of this forum haven't tried this. I won't speak for any other old timer here, but I have tried it as I mentioned in an earlier comment. What I discovered was that it was hit or miss, and therefore a waste of time when your name goes on a repair. Your example, although very interesting, won't sway me at all.

The Andrea I'm working on has a lot more hours than yours (I'd guess it's well over a hundred twenty five hours since February) and 5 of the cans are still good operating fine, but history tells me that they're on bonus time. Using my own TV as an example, two cans were dead immediately, and two failed some 20-30 plus hours after it was running perfectly. The remaining 5 are still running fine at over a hundred hours. They're still coming out.

Sure, you can have capacitors work after 70 or more years, but proving a capacitor can work at 70 years and proving a capacitor can work for 15 hours a week for the next 10 years is another thing entirely.

I mentioned earlier that I'm restoring an 1850s reed organ melodeon. The leather exhauster is still working, but if don't replace the leather, how long will my wife be able to play the melodeon before the leather tears? 10 hours, 100 hours? Maybe she'll never put enough hours on it, but I'm replacing the leather anyway. Once this melodeon is finished, I don't want to ever take it apart again.

That's the point we're trying to make on this subject.

John

+1
I've also reformed and vetted lytics with my Heathkit and watched them fail after dozzens of hours of operation.

I've seen TVs and radios run on original caps and even keep a few that way as shelf queens that rarely get powered. Though even that isn't common since if I power on a display set and it dies on me it could be an embarrassment, and even if it isn't I rather feel confident I can grab anything off my shelf and run it as if I just bought it new without worry.

I put enough hours on my sets to go through certain tubes multiple times. Anything that will help put the next repair farther out into the future and let me tackle repairing something else or let me live my life away from the bench is worth doing.

[Penthode]

Originally Posted by JohnCT

Sure, you can have capacitors work after 70 or more years, but proving a capacitor can work at 70 years and proving a capacitor can work for 15 hours a week for the next 10 years is another thing entirely.

John

I did mention I have a 1949 RCA 8T243 I acquired in 1970 and still runs on its original electrolytics. If I am fortunate to still be alive in 20 years, I will let you know if the capacitors are still okay.

And I generally do not watch 15 hours of TV. I the 721TS case, I simply left it running while going about other things.

I find it very amusing however how some members of this forum take the subject of electrolytic capacitor replacement so very seriously.