RCA TC-127 restoration nearly complete!!

[Tubejunke]

I decided to make a new thread concerning this project. The original thread was named for my original power transformer problems.

In short everything went well with this set. I can rest and play the set with confidence as the ENTIRE power supply was replaced. Also I replaced ALL electrolytic capacitors and 95% of the paper caps. The rest are coming. The remaining caps check OK but I'm still replacing them.

Heres where I stand. The set powers up and dispalys a good picture with low audio output. After about 2 minutes the horizontal lock kind of intermitently comes and goes. When it comes in it is not real stable and may display some horizontal roll and then lock. The adjustment on the back is cranked as far as it can go and so is the hold control. Obviously some component has changed value. I hope it is that mean, ugly, 1000 volt black beauty paper cap that remains. Now the sound problem is a bit more of a mystery as ALL of the caps in that section are new. I found a 150 ohm resistor that had doubled in value. A small improvement maybe but still no cigar. Very low volume..

If I can lick these last small issues I will have one beautiful old RCA to watch for years to come.

I can get more enjoyment out of watching this kind of set than one of these crazy wide/flat things at Wa-Fart that everyone is so worried about.

Kind of A** backward to people I know. Thats the fun of it!

[sean]

If that last black beauty isn't it, check for leaky mica caps in the horizontal oscillator and AFC circuits. I had a set with a horizontal lock problem that turned out being a leaky mica coupling the sync separator to the AFC diode. It put something like 100V on to the 6AL5 that was supposed to only have about 1V on it.

[Tubejunke]

Wow! Come to think of it there is a funny looking mica cap that goes to a 6SN7 that is a sync tube. By funny I mean it is kind of slimy looking where as the others are dry. It does not get hot during use so I left it alone. It seems like there is a theory that ceramics and mica's seldom go bad. Maybe true but that doesent mean that they DONT go bad. I need to remember that.

Here's a good question (or two) that I think we all could use clarity on. Does it matter if you replace say a paper cap with a ceramic disc? Or can you replace the mica cap with an orange drop? I have never understood why old sets have so many different types. There must be a reason. Its seems like this topic has come up before.

I can think of some areas under a chassis where I would like to replace a big paper cap with a modern ceramic disc type.

[ohohyodafarted]

As long as capacitance is the same and the voltage is equal to or greater you should be able to use anything you have. In the past paper was used for larger values and mica or ceramic disc for smaller values. Lots of different voltage ratings were used because higher voltage ratings made the cap so much larger physically that using a lower voltage rating, when possible, meant the component would be much smaller. With the insulation materials used in todays caps, any 2 caps of equal value, todays cap will be smaller than the counterpart of yesteryear.

[John Folsom]

Paper capacitors were used for coupling and bypass where value, stability, and high frequency response were not so critical. Mica caps were used where initial value and/or long term stability with time and temperature were important (such as in timing circuits). Ceramic disc caps were used mostly where high frequency performance is important, such as IF screen bypass. Of course, there are exceptions to these general guidelines, sometimes for reasons which are not obvious. I suspect the choice of capacitor type was sometimes driven by reasons which had little to do with electrical performance considerations, such as availability, cost, or size.

While one could probably substitute disc or mica caps for paper, I would be hesitant to go the other way. Many versions of disc capacitors have large temperature coefficents, which might make them unsuitable for mica replacements.

Given the performance of modern "mylar" type capacitors, there are probably places where mica caps could be replaced with mylar types. But for most of the less than 1000pf values of micas, mylar typer are not available.

Well, that is my 2 cents worth.

[bgadow]

I have read, somewhere online, that discs should not be used in some applications where paper was normally used. I wish I knew the details. One famous example is the high voltage caps in electrostatic deflection circuits.

[Tubejunke]

Good info everyone. Today I ordered a 100 and a 390 mmfd ceramic disc to replace the equal value molded mica caps in the sync section. I hope this will do the trick. I didnt see orange drops of such a small value at high voltage. Luckily there are only 2 or 3 of these to worry with. I think there is another strange kind of cap that I will discuss upon further investigation.

[Tubejunke]

I am going to conclude this long thread with a big thanks for all the help. I will say that every person out there interested in this hobby should do what I call basically a rebuild. I have been toying around with old radios and TVs for 25 years. I feel as if this ONE project taught me more about what is going on in not just a television, but more so a vintage television. There is a big difference.

Through the years I stuck for a long time with thorough cleaning, tube testing, and wire repair for what was mostly a radio collection. My regular use TV sets in the 80's were from the fifties. If I couldnt fix them with new tubes or a CRT I would have to send them to the repair shop. Then I progressed to jumping across to locate bad electrolytic capacitors and checking/replacing resistors which was a big step. I had a lot more working pieces in my collection at that point.

Now I feel I have crossed a new threshold restoring this RCA. All the confusion with color coding of the factory and replacement power transformers taught me a lot about tracing circuits and understanding what makes things tick. I definitly refined my soldering technique to the hilt. It was kind of neat changing maybe 3 to 5 caps a night and watching the set slowly come back to life. Its really amazing and satisfying to see what was a smoking piece of junk once again working nearly as good as the day it came out of the store. Its like raising the Titanic!! A good feeling.

By the way my set was viewable by New Years. I missed my original goal of Christmas and someone suggested going for New Years. So I made it! There are some minor adjustments and the volume is still low, but the picture is VERY chrisp with great sync and size. I should have a very reliable set now. The other working sets that I have never get played longer than maybe 45 minutes at a time. They are all original. No recaps. I can watch this set all afternoon if I want. Great stuff!!

[Chad Hauris]

There are also some types of paper caps that are made to look just like micas...brand name is Micamold. If the cap is a fairly large capacitance value but looks like mica it might actually be paper in disguise.

[Phil Nelson]

My website has a basic recapping article that illustrates the different kinds of old caps, including the paper Micamolds.

http://antiqueradio.org/recap.htm

At least one other company made the "micamold" type paper cap. I found a Solar cap like that once upon a time. It was rectangular, very much like a Micamold, but it had the value stamped in the case rather than using colored dots.

Regarding ceramic disc caps, I have been told to avoid them in frequency-critical applications. I got bitten when I used a ceramic to replace a small-value Black Beauty in the horizontal oscillator circuit of an RCA 21T227.

Teeny-weeny ceramics are easy to damage when soldering them in, and they may also change value as the set heats up. Not cool when you're trying to get your horizontal oscillator to run at the right frequency. When I substituted an orange drop for the ceramic disc, the TV magically started working again.

Ceramics are cheap, but when you consider the number of hours you spend restoring an old TV, I'd prefer not to cheap out on components. You get what you pay for, as the saying goes :-)

Phil Nelson

[Tubejunke]

I'm glad someone pointed out the whole Micamold issue. I was not going to worry about them because I did not know that they are paper. I did replace i because it was all gooey looking like it had been hot. I remember the set having a major improvement when I changed that one. I think there is still 2 or 3 others. I better yank them. Maybe that will take away the few small bugs left. Low sound and sometimes iffy horizontal hold. Sometimes it will lock and then unlock at random. It seems like after a good warm up this problem pretty much goes away.

[Phil Nelson]

Originally Posted by Tubejunke

I did replace i because it was all gooey looking like it had been hot.

You can't tell anything about a capacitor by looking at it, apart from the extreme case in which one has completely exploded.

Beautiful-looking vintage caps may be leaking or totally failed. Gooey-looking ones might test OK for the time being, but should also be replaced if you want your set to work.

Phil Nelson

[Tubejunke]

I found this old thread when I Google d my RCA's model # tonight and decided to revive it with an update as there was a ton of great input from some of the most knowledgeable people here at V-K that I think will be valuable to people who have come here in the 6 years since this restoration. WOW! 6 years really goes by fast!

Anyway, I still have the set and probably always will as it was my first true restoration although I had been buying and tinkering with sets since I was a kid in high school electronics trade class. Since this restoration I obtained an electronics degree at out local college and for now work as a tech in manufacturing which is about all that is left of electronics repair. I hope to move on to bench work repairing the equipment that I get paid to replace currently. Anyone who has worked around production will understand my endeavor to move on to bench work.

So, just last weekend I fired up the RCA and (as always) it came to life almost as if it were on a showroom floor. However, there were and are a couple of issues that came to light not long after the project. I just haven't gotten around to doing the work. First, the set had a relatively low sound level from the get go. I have another more current thread about battles I am fighting getting good performance out of sets that are working off of digital converters or whatnot. So if you look at that thread you will see that I have discovered that the sets antenna input oddly enough works best with one side disconnected. With that I had decent sound, but I have heard much louder. Good enough to fill the room and hear at the other end of my humble abode.

Second, and finally; the vertical circuitry needs something done to it. There is something that I missed as the top inch or so of the raster is shrunk. It's not progressive as the set warms and over time. It comes on that way and stays that way, but can't be adjusted through height and linearity adjustments. I'm thinking that a resistor has drifted out of tolerance, or perhaps one of the potentiometers has done the same.

Other than that all other aspects of the set are perfect and stable. I wouldn't hesitate to watch it for hours although I don't just out of consideration of its antiquity and to keep the 12LP4 going for a few more years. Heck, some of these old sets are gonna make it longer than we will if we treat them right. I hope this thread helps someone new once again, or is just a good read for us veterans of V-K.

[DavGoodlin]

RCA sets seem to present issues that the less-complex sets do not. I always attributed the higher quality of Zenith and RCA to more sophisticated circuits that can present strange symptoms when every component is not up to spec. I say this only after being able to get sets like GE and Muntz looking as good as new without nearly so much effort.

As someone who has started a few TV threads, I understand how subsequent acquisitions can really push back projects. I have wrapped up a few TV "restorations" and had them come back for the finishing touches. The more you stay on them, the more you learn.

[Tubejunke]

Well, as my Philco thread states, NOW I don't have to troubleshoot the sound circuit under false assumptions of the set being at fault, or my restoration. It's always been the way that my coaxial adapter was configured at the antenna inputs! YEAH!

On the topic of DavGoodlin's comparison of better sets with more ciruitry I have to say that I guess all those well paid engineers back in the early days of TV were scrambling to put together sets with any bell or whistle that was electronically possible, or impossible in some cases. Often I feel these "new & improved circuit designs were excuses for elevated retail prices and crafty advertisement to justify them.

So, like the crazy cars that now come standard with every ridiculous amenity that we not so long ago saw as the nice, but not necessarily necessary (LOL) additions that we could pay extra for if we wanted them, or most often just because of the flash value (ie. second paragraph) we Americans love so much we see that there is much more potential for problems with what we see as being a superior product.

So I will continue to drive a 69 Beetle (extra) and would probably choose my uber simple 56 Philco over my 50 RCA if I had to based on simplicity, =longevity, =serviceability.... The VW will get me there and a Muntz or Philco makes the same picture and sound. Well, the Philco will at least!