Restoration Commences on 1947 RCA Victor 721TCS

[Kevin Kuehn]

I guess that just goes to show how history is changing, and I'm Old

[Electronic M]

Originally Posted by Kevin Kuehn

I guess that just goes to show how history is changing, and I'm Old

Technically Canada broadcasts in North America making their transmissions a North American broadsact. So Titan1 must think the USA is in South America...

[vortalexfan]

I think what was being meant by the comment is that Canadian broadcasts and US Broadcasts while they are North American broadcasts, Canadian Broadcasts aren't "American" Broadcasts, as in USA broadcasts, (when one uses the word "American" generically like like what Kevin did in his post, you're not specifying which part of North America, because US broadcasts would be referred to as "American Broadcasts" whereas broadcasts in Canada would be referred to as "Canadian Broadcasts".

That's why you shouldn't use such broad sweeping terms when talking about something like that, because you can easily misidentify things (or countries or broadcast standards) by using such generic terminology like that.

What should of been said was: "Aren't Canadian broadcasts technically "North American Broadcasts"? rather than "Aren't Canadian broadcasts technically "American Broadcasts"?

It removes any ambiguity that could be there, especially when you have a country like the US that has the word "America" in its name ("United States of America") and the occupants of said country are called "Americans", and anything associated with said country is called "American", including its television broadcasts.

I hope that explanation was helpful.

[Penthode]

The set and it's electrolytic capacitors are celebrating their 75th anniversary this year. This past week I sadly had to restuff the last wet electrolytic in my 1935 Scott AllWave 23. The wet electrolytic dried up and lost all its capacitance!

I am running the 721TS about five hours a day on weekdays and about four hours overall on weekends. That is about 30 hours per week. No sign of any problem with the original electrolytics.

Incidentally, CHCH TV in Hamilton Ontario is running Andy Griffith, I Love Lucy, Danny Thomas Show, My Three Sons and Bonanza between 10am and 1pm weekdays and the 721TS is on in the background as I work in my office.

Here is Bonanza photographed off air just now.

[kvflyer]

Looks good of course. I have a 630TS that still has one half of the can electrolytics original. The other half of them were leaky and were rebuilt (stuffed). I found that the ones that are still original were manufactured by the same company; the ones that were leaky were manufactured by a different company. I don't know who the companies were, only that I could tell by construction materials, technique etc. were the same.

Thanks for sharing!

[Penthode]

That is what I found with RCA CTC5 Canadian chassis. The Camden installed Mallory's remained all good. But the Canadian Sprague capacitors mounted on the auxillary 25Hz chassis were bad and refused to reform without appreciable leakage.

Recall I spend a few days slowly reforming the capacitors after the TV sets and remained dorment and unused for many years. Most would come up fine but there are a few that will have a higher leakage. The Spragues becan with a leakage of about 1mA and that current leads to heat dissipation which propagates eventual catastrophic failure. I waited to see what would happen to the Spragues and they were warm in operation. If the capacitor is warm, it will go!

So far the 77 year old units in the 721TS still run cool after an hours operation. So my suggestion before even plugging the set in is to do an assessment and dielectric refomation to ensure leakage is 100uA or less and then give them a try.

[kvflyer]

Yes, it is interesting.

I know that it's a PITA but if there are not a lot of connections on the electrolytic capacitor, I disconnect every lead and test the capacitor for value first and leakage at the working voltage next. If it passes, I put everything back and then monitor the temperature. Sometimes you win, sometimes you lose.

[Penthode]

Originally Posted by kvflyer

Yes, it is interesting.

I know that it's a PITA but if there are not a lot of connections on the electrolytic capacitor, I disconnect every lead and test the capacitor for value first and leakage at the working voltage next. If it passes, I put everything back and then monitor the temperature. Sometimes you win, sometimes you lose.

When I bought this set about 6 years ago, it had sat in an attic for nearly 60 years unpowered. Apart from a mouse nest, it was a pretty clean and intact set. When I began the restoration, I decided to first evaluate the electrolytics. As it had not been powered on for many years, the filter capacitors were extremely leaky. I believe had it been powered as I found it, the capacitors would have been most likely destroyed and the rectifier destroyed.

I proceeded to reform the electrolytics by simply removing the 5U4 rectifier and with power off, connecting my Sprague TO6 supply across the B+ supply line. I limited the current to a maximum of 10mA and left the TO6 running all night. The voltage across the capacitors began to rise from less than 10 volts @ 10mA. I had taken into account any shunt resistance across the B supply and I recall removing some divider resistances.

The next morning the capacitor voltage had reached nearly 100 volts with minimal leakage. I raised the voltage and keeping maximum leakage less than 10mA. By the end of the day the total paralleled capacitor leakage was well under 1mA. I disconnected a few capacitors I could not readily access to ensure leakage was no more than 100uA at full rated voltage.

The point I am making here is that the capacitors will be destroyed unless a more gentle approach is made waking them up. I never use a variac to power up an old device. I will instead immediately look at the electrolytics and evaluate and see if they will reform. Then if the TV set dates prior to 1960, I will replace almost all the paper capacitors.

I have rebuilt a sizable number of electrolytics which will not reform. But with all 5 of my late 40's RCA Televisions, I have only replaced one chassis mount multiple section electrolytic. My CT100 had two bad chassis mount electrolytics and my CTC5 set has retained all the original electrolytics. Curiously, a 1961 CTC 11 RCA color I restored a decade ago required replacement of every chassis mount electrolytic. All but one the dielectric would not reform and the one that did suddenly failed in service. (The failure was not a short but went totally open.)

So there is no hard and fast rule. It is easy to reform the things and to test leakage and capacitance. And the experience I have had has been very good up to now.

[kvflyer]

Originally Posted by Penthode

When I bought this set about 6 years ago, ...

So there is no hard and fast rule. It is easy to reform the things and to test leakage and capacitance. And the experience I have had has been very good up to now.

And that's the key. No two are alike.

[old_tv_nut]

Gorgeous pics!

[Penthode]

Thanks.

[hardpanman]

"The Lady Vanishes".

[dtvmcdonald]

I notice this thread return today. I have a comment on electrolytics.

Earlier this year I opened up and checked the electrolytics on a ~1975 device I have that has run with no repairs for over 250000 hours. They check out fine, low leakage, low ESR, and within spec capacitance. This set ran continuously except for long vacations for over 30 years. It is a Hafler 280 watt audio amp. I also checked the amp's performance, and it meets specs.

Just to be sure, the words are "two hundred fifty thousand hours". The caps are mounted well away from the transformer and heat sinks, and it has been well ventilated.

[stuben]

I’ve had the same experience with equipment that used Sprague Atonms The blue aluminum electrolytics with axial leads. I used to own a dental laboratory which I opened in 1980. One furnace that I fire porcelain in heats a small chamber to 2000 degrees F. Since it was installed it’s never been turned off except for a week or two during vacations. It’s well ventilated with heat sinks to protect critical components. I’ve never bothered to check the capacitors as it still works the way it should nearly 50 years old now.

[Penthode]

Next month it is 6 years since I reformed the electrolytics. I still regularly use the set and all the chassis mount electrolytics remain fine.

Recall the set remained in an attic for over 50 years unpowered. I attribute this the electrolytic capacitor survival to slowly reforming the dielectric. When the capacitors have been reformed, the current should be no more that 200uA at full rated voltage.

Note when I began reforming the capacitors, each began as a near dead short. The initial 10 milliamperes was reached at about 15 volts! Over a period of about six hours, the current dropped slowly until after six hours, the current was 200 uA at the capacitor full rated voltage. Periodic testing showed that the current remained at around 200 uA which is normal for these types of electrolytic capacitors.

Here are some photos 721TS this morning on it's 79 year old electrolytics. The video source this time is a VHS tape of of the motion picture "Mr Smith Goes to Washington" played on my 1977 RCA VBT-200 VHS machine: the first VHS machine introduced to the US market.