Restoration Commences on 1947 RCA Victor 721TCS

[Penthode]

It is up to 45 hours now. I investigated the picture width problem. I just performed routine voltage measurement and found the horizontal oscillator plate voltage a little low. The 120kohm plate dropping resistor had drifted upward to 150kohm. I replaced it with another 120 kohm 1 watt carbon composition resistor (originality of course) and the width was restored.

I saw the width control adjustment was screwed all the way in to maximum before the set was allegedly retired to the attic 60 years ago. So this must have been an old fault.

I have reverted testing with an older expiring 10BP4 to continue waiting for the anticipated expiry of the electrolytics. I want no more hours than necessary on the CRT.

Somehow I don't think there is going to be a failure. The electrolytics are running cool. And this hasn't been luck or good fortune: my two other pre-1950 RCA tv's have all their original electrolytics and run fine. It is running now and has done another 10 hours continuous running today.

The key is patience reforming the capacitors. That is leaving them attached to a light trickle current 24 hours and slowly reaching the rated maximum voltage. If you do not hurry the process, the capacitors should survive. And I am only speaking for RCA sets: I cannot speak for other manufacturer's sets designed to a budget.

Will aim for 55 hours running time tomorrow.

[JohnCT]

Originally Posted by Penthode

And I am only speaking for RCA sets: I cannot speak for other manufacturer's sets designed to a budget.

When I started in the TV biz in the early 70s, I replaced many hundreds of can electrics in all brands, RCAs included. Some were from the 50s but most were from the 60s.

Recently, I've restuffed cans that were fine, and every time a little investigation reveals decay in both the foil and the paper. It's actually amazing they work at all at this age.

No amount of reforming will improve the deterioration of the paper or foil or reconstitute dried electrolyte.

John

[Penthode]

Originally Posted by JohnCT

When I started in the TV biz in the early 70s, I replaced many hundreds of can electrics in all brands, RCAs included. Some were from the 50s but most were from the 60s.

Recently, I've restuffed cans that were fine, and every time a little investigation reveals decay in both the foil and the paper. It's actually amazing they work at all at this age.

No amount of reforming will improve the deterioration of the paper or foil or reconstitute dried electrolyte.

John

Can you quantify the decay you have seen? I mean, what specifically quantifies the intenal degradation of a capacitor that deems it unservicable to you?

Do you replace the resistors and full tube compliment as well, even though they function out of tolerance? The curious thing here is that these reformed old electrolytics after dozens of hours test within original tolerance for leakage and capacity. The vacuum tubes from day one lead a downward spiral and after 13 years of heavy use have degraded.

Is it not of interest that after 43 hours continuous operation the capacitors still run cool and are within the original specifications? This is not loose speculation.

Have you tried to patiently reform the capacitors as I have outlined here? Surely old chassis's are available to try. And if it is your own personal set, what is there to lose? Worried about the power transformer or rectifier? You can always insert a slow blow fuse.

I will reitterate that the capacitors remain healthy after 43 hours continuous operation. How many hours operation will it take to convince?

[JohnCT]

Originally Posted by Penthode

Can you quantify the decay you have seen? I mean, what specifically quantifies the intenal degradation of a capacitor that deems it unservicable to you?

Yes. The foil as it's unwrapped is generally full of pin holes or outright disintegrates when unwrapped. The paper was mostly just falling apart. How these filters worked at all is amazing.

Do you replace the resistors and full tube compliment as well, even though they function out of tolerance?

No. Resistors, tubes, inductors etc. are different animals.

The curious thing here is that these reformed old electrolytics after dozens of hours test within original tolerance for leakage and capacity.

Which is still higher than a new electrolytic when it comes to leakage readings, and you are talking about a capacitor that is working right now. What happens six months from now?

The vacuum tubes from day one lead a downward spiral and after 13 years of heavy use have degraded.

Tubes wear out faster than other parts yes, which is why they were put in sockets in most cases. But a worn out tube doesn't generally destroy a transformer when it wears out. Sure, certain tube failures cause collateral damage, but even a brand new tube can do that.

Is it not of interest that after 43 hours continuous operation the capacitors still run cool and are within the original specifications?

In the interest of discussion perhaps, but I have no interest in using this single case anecdotal evidence to change what I know as fact.

Have you tried to patiently reform the capacitors as I have outlined here?

Yes. I used to try to save a buck like anyone else. When I first started screwing around with tube radios for my customers in the 80s I would do this. I got tired of seeing the same radio back months or a year later with a bad electrolytic or bad paper cap.

When I restore a radio for a customer, I guarantee it for a full year except for vacuum tubes.

I will reitterate that the capacitors remain healthy after 43 hours continuous operation. How many hours operation will it take to convince?

There is no amount of hours for this one TV that will change my mind on this. The 51 Andrea I'm finishing up has 5 of its original 9 can filters still installed. Two of them let go after dozens of hours of working perfectly.

The other two I restuffed for restoration sake were physically degrading in the manner I described in my first paragraph.

I'm not one to change every part because it's what is expected, I change parts that are either defective or have a history of failing. I have a 1929 Radiola in my living room that is running on all original parts, capacitors included with the exception of 5 of it's globe tubes. The Radiola was built in an era before electrolytics and the capacitors were made with rice paper instead of rag paper. Radiola experts say don't change them unless necessary and indeed, my Radiola has been running 15 years in the time I've had it on original caps.

John

[Penthode]

Originally Posted by JohnCT

Yes. The foil as it's unwrapped is generally full of pin holes or outright disintegrates when unwrapped. The paper was mostly just falling apart. How these filters worked at all is amazing.

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

Which is still higher than a new electrolytic when it comes to leakage readings, and you are talking about a capacitor that is working right now. What happens six months from now?

As pointed out, I have owned an RCA 8T243 from 1949 for 50 years and it retains its original electrolytics. And they remain fine.

In the interest of discussion perhaps, but I have no interest in using this single case anecdotal evidence to change what I know as fact.

Your statement points only to your anecdotal evidence. You are by rote used to changing the capacitors. And as this is supposed to be a hobby dealing with archaic artifacts (ancient TVs) and not with a NASA space project, what is the harm in attempting to retain the set's originality? I am the owner and I will maintain a watchful eye.

Yes. I used to try to save a buck like anyone else. When I first started screwing around with tube radios for my customers in the 80s I would do this. I got tired of seeing the same radio back months or a year later with a bad electrolytic or bad paper cap.

When I restore a radio for a customer, I guarantee it for a full year except for vacuum tubes.

But as I earlier pointed out, this is not for a customer. This is for myself. I would agree with you if the set was out of your control, yes the capacitors should be changed.

And it has nothing to do with saving a few bucks. It is the aspect beyond simply cabinet aesthetics, to retain the historical originality of the set and to make "intelligent" decisions what to retain and to replace. As a professional Electronics Engineer with an MSEE, I precisely know what I am doing.

There is no amount of hours for this one TV that will change my mind on this. The 51 Andrea I'm finishing up has 5 of its original 9 can filters still installed. Two of them let go after dozens of hours of working perfectly.

I cannot comment on the quality of the capacitors used or whether you reformed the capacitors properly. I contend that the capacitors you attempted to use did not reform properly as can be determined by properly applying a stress test of leakage measurement at full rated voltage. If determined that the capacitor is in anyway compromised it must be replaced. In my 721TS case, after reforming, the leakage was well within spec at full rated voltage, which encouraged me to run this test.

Anyhow I shall run the set for another 10 hours today. After it goes beyond 50 hours, I shall test some of the electrolytics and confirm whether or not the capacitors have degraded in capacity or leakage over the 50 hours running time.

[JohnCT]

Originally Posted by Penthode

But as I earlier pointed out, this is not for a customer. This is for myself. I would agree with you if the set was out of your control, yes the capacitors should be changed.

That's kind of the whole point, isn't it? Your RCA may never have those filters fail and I hope that's what the end result is.

But even when rebuilding something for myself, I do it with the expectation that any future failures will be minor in scope, and it will have a projected life as long or longer than when it was first made. In my store I have my 1936 Philco 60 cathedral that I restored 4 years ago. It's a great conversation piece and so many people are amazed it works. It plays every day from when I get there about 9AM until I close about 4PM. Sometimes I forget to turn it off and it runs overnight or over a weekend. In four years, it only has needed an output tube.

The Andrea 16" TV I'm restoring will go in my front living room with my Radiola and 1850s Smith reed melodeon, and it will be with the expectation that I won't have to repair it except for maybe vacuum tubes at some point. I'll keep my fingers crossed that "hard" parts like the transformers, yoke, CRT etc. will live a long life.

I put the Andrea aside for now as I'm trying to build an exhauster and bellows for the Smith melodeon, but when I get back to restuffing the rest of the cans in the Andrea, I'll take some pictures and post what the cans look like when unrolled.

John

[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.

[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.