Restoration Commences on 1947 RCA Victor 721TCS

[init4fun]

Originally Posted by dtvmcdonald

I have always been of the impression that electrolytics that are bone dry
cannot out damn bug! OUT! you damn cockroach get out of my keyboard reform.
Reforming is supposed to take solvent.

I have seen caps that were bone dry and had normal capacitance and
took rated voltage, but I assumed that they were that way before going dry.
What think you people.

I hope you fry, damn bug ... wait, no, that might hurt the keyboard. OUT!
Damn coronavirus, keeping the exterminators away!

Not fair to be drinking and not share with your old TV buddies .....

[Electronic M]

Originally Posted by init4fun

Not fair to be drinking and not share with your old TV buddies .....

Yeah!

[old_coot88]

https://www.youtube.com/results?sear...ry=i+like+beer

[Penthode]

I ran the 721TS another 5 hours today. Ran three movies and film shorts from a TCM DVD.

Electrolytics still fine. Each running cool. Rest of the wax capacitors I chose to reprieve okay. Yesterday when I tested the resistors in the video amplifier, all were within tolerance.

When I obtained this set the width adjustment was set for maximum width. As is, the image on the 10BP4 just fills the mask. Might look around the sweep section to investigate. Certainly the width and height have remained constant over the period of my bench test.

Consider this set sat in a partially insulated attic for over 50 years and the sat in storage for a further seven. I am fortunate it had a quiet existence which may partially explain why much of the original componentry has survived.

Will keep it running to determine if anything will fail. I suppose 35 hours is insufficient to prove that original electrolytics aren't salvageable. So let's give it another 35 hours. I am curious to see myself.

Here are another couple of screenshots from a few minutes ago.

[Penthode]

The set has been on for six hours today. Finished off the Judy Garland - Mickey Rooney DVDs. Looking at some late 20's Vitaphone shorts. Here is Blossom Seeley in 1927.

The original electrolytics are still running cool and fine after over 41 hours. Still waiting for them to fail.

[Penthode]

Finished off another 8 hours running DVDs on the 721TS now reaching 43 hours since reforming the original electrolytic capacitors. I am impressed with the performance of this set with only 21 tubes. Lots of audio volume, no buzz likely because of its full split sound design. The video is sharp but the resolution above 3MHz is missing since the design has only three IF stages. The lack of any AGC is not a problem with no analog over the air available. Would have been curious how it would have been necessary to adjust the contrast control when switching between local and fringe stations.

I recall using my RCA 8T243 (kcs28 chassis) for analog over the air. This is the set I have kept the longest, having been given it in 1970. (It incidentally still runs on its ordinal elwctrolytics). The high class RCA design for 1948-49 sets feature full 4 MHz resolution, a more sophisticated sync separator and RCA's first television AGC solution using peak sync detection. But most impressive were the dual adjacent channel traps. Despite the wider bandwidth, the adjacent channel rejection was so good, you were able to receive deep fringe signals immediately adjacent to strong local stations. The 721TS had no adjacent channel traps. No problem with a modulator now feeding the set.

But the RCA sets in the late forties were built like tanks. Later design sets, especially with larger screens and with larger deflection angle CRTs put a stress on all of the components which would result in reduced reliability.

So tomorrow we should hopefully be able to reach 50 hours on the original 73 year old electrolytic capacitors.

[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.

[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

[Kevin Kuehn]

Originally Posted by Penthode

But the RCA sets in the late forties were built like tanks. Later design sets, especially with larger screens and with larger deflection angle CRTs put a stress on all of the components which would result in reduced reliability.

What are your thoughts on the air core high voltage transformer that RCA started using around 1950? I'm assuming it had something to do with the new wider deflection CRT's, although other manufactures seemed to be using something like a ferrite core flyback transformer with good success. It appears that they used that air core on everything from a 12" to 19" CRT.

[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

[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.