Restoration Commences on 1947 RCA Victor 721TCS

[irext]

My method for reforming electrolytics is to use a low current high voltage supply and place a 10K resistor in series with the cap being reformed. I monitor the voltage across the cap which will slowly rise if the cap is a good candidate. I'll monitor the voltage as it rises to the cap's rated voltage then remove and gently discharge the cap and reconnect to the test rig. If the cap is decent it will much more quickly charge to it's rated voltage the second and subsequent times. Interestingly if the process is stopped before the cap reaches it's rated voltage, discharged and reconnected to the rig it will quickly rise to the voltage it got to when it was disconnected and then proceed slowly to it's rated voltage, sort of behaving like a zener diode! I have a 1956 B&W PYE set I've restored and managed to reform all of the multi electrolytic cans. The set has done countless hours with these but it is only used by me. If I was restoring it for someone else I would definitely re stuff the can's. I still have a healthy disrespect of all old electrolytics.

[Polaraligned]

Well, kudos to whatever electrolytics RCA used. Personally, I just want my sets to run reliably, so I just replace the electrolytics seeing as though they may not be whatever brand/spec that RCA used. Not all electrolytics are this marvelous.

It seems like during the course of this you have had a number of resistors fail. Maybe I should be replacing all the resistors for reliability, LOL.

[Penthode]

Curious I found RCA electrolytics have been vey reliable. I had a 1949 9TC275 set with a slew of bad electrolytics it was stored in a wet basement in Chicago which may account for it. I have four other late '40's RCAs and all have original electrolytics. As I pointed out, the slow reforming did the trick: limiting the maximum current during reforming to no more than 10mA. And never applying power to the set until it has first been thoroughly vetted. Variacs and direct power application after sitting dormant for 50 years is a sure killer.

As for overall reliability over the last 6 months, the little 721TS has only had the one resistor failure in service. It just suddenly opened up.

[Tube TV]

I don't know how I've missed this thread this long. It's been a good read though.

My 1954 Crosley is running on the original electrolytic cans. I tested them in 2006 and they all sections checked out fine so I never bothered to change them. I have no idea how many hours I have on that set, but it was used daily fom fall of 2006 to around 2011 and less frequently after that, and have had no issues with the electrolytic can. I tested it in the winter of 2015 while I had the chassis out working on a intermittent lose of horizontal oscillation and it still tested out fine. It's also running on the original selenium rectifiers too.

[Jeffhs]

Originally Posted by Tube TV

I don't know how I've missed this thread this long. It's been a good read though.

My 1954 Crosley is running on the original electrolytic cans. I tested them in 2006 and they all sections checked out fine so I never bothered to change them. I have no idea how many hours I have on that set, but it was used daily fom fall of 2006 to around 2011 and less frequently after that, and have had no issues with the electrolytic can. I tested it in the winter of 2015 while I had the chassis out working on a intermittent lose of horizontal oscillation and it still tested out fine. It's also running on the original selenium rectifiers too.

The electrolytics in your TV are nothing short of amazing, if they have lasted 67 years and are still going strong -- especially if the set was used daily from 2006 to 2011. In most TVs, these capacitors would have failed (shorted, leaky, etc.) by now. What is the secret, if any, to your set's original electrolytics having lasted this long?

That your TV itself is still working is amazing as well, especially after 67 years. Are you using this set as a video monitor for games, a computer, etc., or, if you are still watching TV with it, are you using a DTV converter or a cable box?

[Penthode]

It may appear unusual that the Crosley or RCA electrolytics have survived 70 years. I think it should be less surprising if the electrolytics are made by Sprague or Mallory.

[Tube TV]

Originally Posted by Jeffhs

The electrolytics in your TV are nothing short of amazing, if they have lasted 67 years and are still going strong -- especially if the set was used daily from 2006 to 2011. In most TVs, these capacitors would have failed (shorted, leaky, etc.) by now. What is the secret, if any, to your set's original electrolytics having lasted this long?

That your TV itself is still working is amazing as well, especially after 67 years. Are you using this set as a video monitor for games, a computer, etc., or, if you are still watching TV with it, are you using a DTV converter or a cable box?

I used to use it for OTA TV back when analog was still on, then I switched over to just the VCR and DVD. I don't know what the secret is, I just let them charge on a capactor tester and bump the voltage up when they test no leakage at that voltage.


Most of my test equipment is running the original electrlytic cans as well and it's all 1950's early 60's gear.
The newest gear on my bench is a B&K Television Analyst 1076.

Sets I've pulled out of damp garages and basements seem to be the ones that have bad electolytic cans. They'll start gassing around the terminal pins. I guess the moisture gets in there with time.

[marcel]

Wrong message, how to delete this message?

[Penthode]

Well it is over a thousand hours now. I have the set in my work office and leave it running through the day. The electrolytics show no sign of failing.

The KRK2 tuner has however a problem with the fine tuning capacitor. The rotating capacitor shaft is loose making it awkward yo find tune. Purely a mechanical problem I will investigate next week.

[Kevin Kuehn]

Originally Posted by Penthode

Well it is over a thousand hours now. I have the set in my work office and leave it running through the day. The electrolytics show no sign of failing.

The KRK2 tuner has however a problem with the fine tuning capacitor. The rotating capacitor shaft is loose making it awkward yo find tune. Purely a mechanical problem I will investigate next week.

How are the CRT and receiving tubes faring after 1000 hours? Just putting this into perspective, we've put 1000 hours on a riding lawnmower over a period of 8 years and consider that it's fully depreciated. Likewise it's a remarkable amount of TV time and quite a testament to late 40's electronic technology. In so many ways this has been one remarkable TV.

[Penthode]

Originally Posted by Kevin Kuehn

How are the CRT and receiving tubes faring after 1000 hours? Just putting this into perspective, we've put 1000 hours on a riding lawnmower over a period of 8 years and consider that it's fully depreciated. Likewise it's a remarkable amount of TV time and quite a testament to late 40's electronic technology. In so many ways this has been one remarkable TV.

That is a good question. I tested the tubes on my AVO MkIII tranconductance tester when I was resusitating this set. The set has required a touch up of vertical height and linearity. Curiously I had to reduce width slightly. As far as RF sensitivity or the quality of video and audio, no noticeable degradation.

A few carbon resistors discovered drifted when initial restoration and troubleshooting were replaced. I only tested and changed resistors which obviously would affect performance. An example was insufficient horizontal drive due to the oscillator plate supply resistor drifting upward. I intentionally replaced the resistors with period new old stock carbon resistors.

Recall I only changed the paper capacitors for which leakage would cause bias problems. That is if leakage was acceptable in the circuit, I left it in. That accounts for about a quarter of the original paper caps remaining. All of the original electrolytic chassis mounted cans after 1000 hours remain healthy which is remarkable after 75 years.

The CRT was a late 50's replacement shortly before the set was put into storage and so the emission remains good. Typical of late 40's CRTs, the focus isn't perfect across the entire CRT but the set does provide a decent picture.

In summary, I think the greatest concern for reliability back then and now is the paper capacitors. In order to make a reliable yet as original as possible set, a lot of thought was given to the restoration strategy. This included understanding how the circuits functioned and anticipating problems. Certainly during the initial extensive bench test monitoring a close eye was kept on the original electrolytics for failure. After 1000 hours they are still fine.

It is a daily runner: I had the set on today for about 5 hours. It will probably be on for about 10 hours this weekend.

[Penthode]

The RCA 721TS has been running continuously for 10 hours today. I switched it on at 8:30am and it is now past 6:30pm. It keeps me company while I work at home.

It is still running on it's original electrolytics and I am still waiting for them to fail after 1000 hrs plus.

[DavGoodlin]

I have four TVs using this chassis I haven't gotten to restore. a 721 I just picked up, two 8T241s and a 9T240.

This thread is encouraging because I dread replacing the dozen or more electro's these particular RCAs use.

Among my 21" sets, whatever Zenith used in '66 and 67' had reformed well.
BUT the two CTC-11's, 12's, 16x and 20c ALL needed the electrolytics replaced just to get rid of all the lingering issues caused.

I suspect the common ground fails and other things happen to these cans, creating high impedance connections internally due to corrosion from humidity, freezing and other factors.

[Penthode]

Originally Posted by DavGoodlin

.

Among my 21" sets, whatever Zenith used in '66 and 67' had reformed well.
BUT the two CTC-11's, 12's, 16x and 20c ALL needed the electrolytics replaced just to get rid of all the lingering issues caused.

I suspect the common ground fails and other things happen to these cans, creating high impedance connections internally due to corrosion from humidity, freezing and other factors.

Interesting as I have found similar. Mt RCA CTC-11 all of the original electrolytics were bad and had to be replaced. I replaced all apart from one supplying the B+ to the Vertical output and after a month it failed. The failure mode was opening up rather than shorting.

I have besides the 721TCS, an 8T243, 8TC271 and 9TC275. Each of the chassis mount capacitors reformed okay except for the 9TC275 under chassis mount capacitor. And my CTC5 had one electrolytic fail at turn on. But is was on the 25Hz subchassis added by RCA Montreal. The Camden mounted capacitors were excellent. (I suspected the Canadian electrolytics would fail as the leakage approached 1mA after reforming at full rated voltage whereas the Camden capacitors were at or under 100uA.

I think the takeaway here is after reforming, testing at full rated voltage or 10 % above, leaving it connected for aat least 30 minutes at this state (to check for thermal runaway) and ensuring the leakage remains no higher than 200uA. And of course after this it retains it's specified capacitance. If it can survive this punishment, then it will be okay in service.

[Titan1a]

No.