Restoration Commences on 1947 RCA Victor 721TCS

[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.

[Penthode]

Last night an electrolytic died in my RCA CTC-5 Whitby shortly after switching it on. I had reformed all the electrolytics and replaced all the paper capacitors when i restored the set in 2012.

The capacitor that died was a Canadian made Mallory on the 25Hz subchassis! The additional subchassis weighs about 35 lbs And contains a massive B supply power transformer, choke and two 80ufd 450v capacitors. The additional filtering was to help minimize the 25 Hz ripple.

The set itself was manufactured in Camden NJ and must have gone by Montreal for the modification. I found that the modification was not well done initially: I found the power lead to the chassis interlock socket was never soldered. It had been like that for over 55 years and there was signs of arcing. Amazing as it must have been bothersome although the set had low hours and I expect the original owners gave up on it.

The Camden capacitors are all Sprague and were very healthy when reformed: the leakage after careful reforming was below 100 uA at full rated voltage. The Mallories were much more leaky at about 1 mA at full voltage. I was tempted to replace them in 2012 but as they did not get warm in operation, I decided to give them a chance. The set subsequently has had a fair bit of use over the last 9 years so I won't complain.

The short took out one of the 5U4 rectifiers and a 15 amp household fuse and nothing else. As you can see the auxillary B supply and the replacement chassis mounted filament transformers are massive and escaped unscathed.

From the photo, the replacement capacitor is in the short can (the old can cut open and restuffed) and it's original companio for testing. After running the set for an hour, it is fine. However I think I will restuff the other Mallory as I have now no trust in it and it may fail in the next 5 to 10 years.

[Penthode]

The 1947 RCA 721 TS is still soldiering on with it's original chassis mount electrolytics. It is coming up to a year and 7 months since my minimal rehabilitation. The axial lead 20ufd electrolytic used for audio output plate and screen bypassing was replaced as it failed my leakage test after reforming. To remind all, two resistors, three tubes, fourteen paper capacitors. Recall I left some of the paper capacitors in if they did not upset any DC levels.

I expect it has close to 1400 hours now.

CHCH TV channel 11 went on air in 1954 and their daytime peogramming in HD are retro programs from the 50's thru the 70's. Oddly, the stations do not multiplex up here probably due to the Canadian media monopoly which favors cable and satellite over terrestrial television. Even the CBC tried to abandon terrestrial TV but failed and only run minimal services over the air.

Anyhow CHCH which appears to be about the last independent terrestrial broadcaster in Canada uses the original 1950's logo mascot. I captured a snapshot off air on the 721TS a few minutes ago with a snapshot from the web.

[Kevin Kuehn]

That is pretty cool to have that old station broadcasting vintage shows. Are you feeding the TV with luma only from a converter box?

[Penthode]

Originally Posted by Kevin Kuehn

That is pretty cool to have that old station broadcasting vintage shows. Are you feeding the TV with luma only from a converter box?

No the box unfortunately has composite video out. Even though this was a cheaper line RCA set with only three video IF stages, you can still make out the color dots on saturated colors.

The tubes are doing well. I never actually tested them but I see no appreciable aging. The CRT was a replacement CBS Hytron from around 1957 and has low hours. I bought the set from just outside Schenectady (it must have received first WRGB which claims to be the oldest TV station in the U.S.) from the original owners. I mentioned earlier in this thread how the family retired the set to the attic around 1960 where it sat for 55 years. It was in remarkably good shape apart the laquer finish flaking and from mice nesting under the chassis. (When I pulled the chassis, it was filled with cotten. Only the focus wire was partially nibbled). Most of the tubes are original RCA and so this set must have had a fairly light life.

[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.

[Jeffhs]

Originally Posted by Penthode

The 1947 RCA 721 TS is still soldiering on with it's original chassis mount electrolytics. It is coming up to a year and 7 months since my minimal rehabilitation. The axial lead 20ufd electrolytic used for audio output plate and screen bypassing was replaced as it failed my leakage test after reforming. To remind all, two resistors, three tubes, fourteen paper capacitors. Recall I left some of the paper capacitors in if they did not upset any DC levels.

I expect it has close to 1400 hours now.

CHCH TV channel 11 went on air in 1954 and their daytime peogramming in HD are retro programs from the 50's thru the 70's. Oddly, the stations do not multiplex up here probably due to the Canadian media monopoly which favors cable and satellite over terrestrial television. Even the CBC tried to abandon terrestrial TV but failed and only run minimal services over the air.

Anyhow CHCH which appears to be about the last independent terrestrial broadcaster in Canada uses the original 1950's logo mascot. I captured a snapshot off air on the 721TS a few minutes ago with a snapshot from the web.

Do you get any American TV stations OTA (or are such stations available on cable) where you are, or is it all Canadian? I would think you would get a few American stations there, as most American cities close to Canada will receive at least one U.S. station (for example, in Detroit, Michigan, viewers can get CBET-TV channel 9, formerly CKLW-TV). I mention CBET because it can be received in my area near Cleveland, when the atmospheric conditions are right; the station is also available in Detroit, which has channels 2 (Fox, formerly CBS), 4 (NBC), 7 (ABC), 50, 56 and 62 (the last being CBS; this station took the CBS affiliation from channel 2 some time ago, in the same manner as CBS-TV in Cleveland was moved from channel 8 to channel 19 (!) in the late 1980s; this was a very stupid move, in my opinion, since channel 19 is a UHF station which is not received well in some parts of northeastern Ohio unless you have cable, satellite or YouTube TV).

[Penthode]

In the analog tv days, it was relatively easy to receive OTA from Buffalo NY from the Toronto area. I am to the west of Toronto on the Niagara escarpment and from here you could receive Buffalo NY, Erie PA and Cleveland OH. witha 50 foot tower and a good antenna.

Those were the VHF days. Now that most of the stations have moved to UHF, reception is more difficult. But can still pick up a few US stations but not as before.

It is frustrating because the Canadian media monopolies of Rogers-Bell-Shaw have no interest in OTA television as their primary interest is the ever diminishing revenue from their cable and satellite monopolies.