RCA Model CTC-11C Color Television (1961)

              

This is my third RCA CTC-11 color television. I usually try to avoid repeating projects, but the $30 price tag on this set was too good to resist. As I was soon to find, this TV required surprisingly little restoration.

The next photos show my two other TVs in the CTC-11 series. The first is another CTC-11C in a mahogany cabinet and the second is a CTC-11H in a black metal cabinet.

  

RCA produced dozens of model variations in the CTC-11 line, with different cabinets and a few optional features such as UHF tuning or remote control, but they are all essentially the same inside.

By the time it produced the CTC-11, RCA had worked out a lot of the kinks in color TV design. This television is both simpler and more reliable than my earlier sets, such as the CT-100 or CTC-4 or CTC-7. Technology had also produced some better-quality components by that time. Instead of paper wax capacitors, the CTC-11 mostly uses dipped mylar caps, a more reliable type. Consequently, all of my CTC-11s were able to produce a color picture without any restoration work. Here are initial screen shots from my other CTC-11C and my CTC-11H:

  

Those pictures aren't perfect—nobody should expect perfection from an untouched 50-year old television—but they show that those TVs were basically operational as found.

The challenge in restoring such a TV is not to bring it back from the dead, but to make it safe and reliable, and tune up its performance without degrading circuits that already work well.

Finding a CTC-11

I found this set in a craigslist ad. A local church had gotten it to use as an event prop and they simply wanted to get it out of their storage room. They had purchased it from the proverbial little old lady who always kept it indoors.

I took the following photos on the day when I brought the TV home. This cabinet style was called the "Cheltenham" and it has a light maple color. I removed the wooden legs to place it on my rolling work table.

  

The rear view shows the interior after I had brushed and vacuumed out some dust. A stamp on the chassis apron identifies this as a model CTC-11C.

These photos show more interior details. The chassis is quite clean and this TV features dual speakers, a woofer and tweeter.

  

Initial Tests and Cleaning

The first order of business with every vintage television is to test its picture tube. If the all-important CRT is dead, some TVs are not worth bringing home.

Before buying the TV, I made a quick initial check with my Sencore CR-70 tester. The emission needle hovered down in the Bad zone, but I knew enough not to be fooled by immediate results. Within a couple of minutes the needle began to creep slowly upward. That was enough to convince me to risk $30.

After I brought it home, I reconnected the tester and let the CRT "cook" longer under normal filament voltage. The needle continued to climb, well up into the Good emission zone.

I have seen the same results with many picture tubes that sat unused for years. The CRT looks dead at first, but it soon revives and gives normal emission after the filament bakes for a while. If you find a picture tube that seems dead at first glance, give it a chance to resuscitate naturally before you try any rejuvenation or restoration operations with your CRT tester, which may do more harm than good. As I was soon to see, this tube is still strong enough to produce a bright, vibrant color picture.

While cleaning the picture tube, I saw that its serial tag matches the number on the chassis serial tag. Not only is this a one-owner television, but it still has its original picture tube!

  

The CRT base shows that this is an original-recipe 21FB22 tube, with a date code that I can't decipher, although perhaps the 60 at the end indicates 1960. In any case, the presence of a strong original picture tube confirms that this is a low-mileage TV, indeed.

These photos show the chassis after I removed it from the cabinet. Having restored two CTC-11s already, this is very familiar territory.

  

I proceeded to test all of the TV's small tubes, cleaning their pins and sockets as I went. All of them tested good! The CTC-11's tubes are listed in my other CTC-11C article.

I also cleaned the TV's potentiometers and performed some basic safety checks of its power supply. You can read more about such preliminaries in my article, First Steps in Restoration.

While you are cleaning controls on a CTC-11, don't overlook the little Service Switch in back. As I learned in my second CTC-11 project, a dirty switch can result in a very strange picture—or even no picture at all.

A visual inspection didn't reveal any horrors, but I did notice this old service tag from February 19, 1963. I guess the owner lived in Seattle at the time.

This TV was only about two years old in 1963, so I suppose the service was for something minor.

When cleaning inside the high-voltage cage, I found a few drips of melted wax under the flyback transformer. That's common in my experience, not a cause for immediate alarm.

I found two broken parts of a disc when cleaning up the empty cabinet, and one glance under the chassis showed me where they came from. Can you guess what's wrong in this photo?

The two disc fragments in my fingers are all that remains of the TV's power-supply thermistor (R188 in the Sams manual). Yellow arrows mark the spots where the part should be connected. After this thermistor failed and fell apart, the repairman simply twisted together its old leads to make a short circuit there. Definitely a service no-no! If this was the service that occasioned the repair tag, I hope the guy didn't charge much.

The thermistor is normally wired between the power switch and the power transformer and its purpose is to soften the powerful inrush of current when you switch on the TV, protecting the TV's other components. A thermistor is a special kind of resistor whose resistance decreases when it warms up; this one has a cold resistance of 79 ohms, which decreases to near zero in a few seconds.

Thermistors were a high-failure component in this design. None of my three CTC-11s still had its original thermistor. In my CTC-11H, the disc remained in one piece but one lead popped loose from overheating, creating a no-power condition:

I wrote "thermistor" in my list of replacement parts to order for this set. In the meantime, while I'm still judging the TV's reliability, I'll soft-start it manually with a variac.

First Power

Enough with the preliminaries! I placed the chassis behind the cabinet and reconnected its cables to the picture tube, convergence board, and speakers. This arrangement lets me operate the TV normally, with both sides of the chassis accessible for measurements. (Don't forget to run a ground line to the metal shroud that encloses the CRT bell, for proper aquadag grounding.)

The black cylindrical gizmo at lower left inside the cabinet is my 7.5-amp variac, which I used to slowly increase the line voltage when turning the TV on. Atop the cabinet is a test pattern generator and behind the chassis is my oscilloscope. If you look carefully past the left side of the cabinet, you'll see my little serviceman's mirror, set up on a chair so that I can view test patterns on the screen (at least, part of it) while standing at the chassis and adjusting controls.

At this stage, I was pretty confident that the screen would light up, but I crossed my fingers as I connected an ammeter and watched the TV's current draw while running up the line voltage. Sure enough, a picture appeared on the screen (here, the TV is receiving a cable broadcast via rabbit ears from my in-house TV transmitter).

That's a coherent screen image with decent contrast and brightness, solid horizontal lock, and semi-stable vertical lock. Not bad! Yes, the picture has a total absence of green, but there's plenty of red and blue, and the missing green is likely due to the fact that I turned all of the set's potentiometers while cleaning them.

The audio was outstanding: rich and full, without a trace of background hum. After some quick twiddling of controls I was able to get plenty of green. (Specifically, I worked through the Sams gray scale adjustment procedure, using the Bias and R-G-B Screen controls along with the Service Switch and the Red and Green Drive controls.)

I measured the B+ supply voltages and the voltages at a few other key spots, and they were all within reasonable bounds. Holding my fingers to the big electrolytic cans, I felt no heat at all. I didn't hear any ominous sounds except for a faint tick every now and then, as parts warmed up for the first time in decades.

Disregarding the misadjusted screen colors for the moment, I used the oscilloscope to check the horizontal and vertical waveforms. The next four images show the waveforms at the 6EM7 tube. The first pair shows the trace observed at the vertical oscillator grid, next to the model trace from the RCA Field Service Guide. The second pair shows the vertical output grid waveform next to its model from the manual.

        

What you want to see at these test points is a clean, stable waveform with approximately the right shape. My unrestored TV is producing waveforms close to the ideal.

The key horizontal waveforms also looked good, which was even more welcome news. The horizontal circuits are even more critical than the vertical sweep circuits. They run at a much higher frequency and, in addition to keeping the image coherent, they produce high voltage. They also generate a keying signal for this set's AGC (automatic gain control) circuit, which affects the TV's RF and IF sections.

Recapping the Sweep Boards

Despite these encouraging signs, I replaced the tubular capacitors on the vertical and horizontal sweep boards. The vertical was not entirely stable, and the sweep circuits are often the most failure-prone parts of any television. Better safe than sorry!

The next photo shows the replaced capacitors, next to a well-thumbed Sams manual page from my previous CTC-11 projects:

I later replaced an electrolytic cap (C6 in Sams) on the vertical board, after the needed part came in the mail.

A Better Picture!

I retried the television after replacing those caps. The vertical stability was improved and the horizontal lock was as good as ever. I spent a little time adjusting some color controls and took this photo:

Close-up images like this are good for judging a color TV's performance. Flesh tones are a complex mix of colors, and all of us know exactly what a human face should look like. Unless the color rendering is pretty accurate, an image like this won't look right.

Testing Resistances and Voltages

I now embarked on a long round of testing, methodically checking the resistance at every pin of every tube in the TV and comparing the results to the resistance chart in the Sams manual.

What you're looking for in this tedious exercise are anomalies—readings significantly different than those recorded by the RCA engineers. Once again, I found nothing alarming.

The next phase was voltage readings. None of my service docs contained a full voltage chart, but I did have two versions of the schematic—one in the Sams Photofact and the other in the RCA Field Service Manual—and each version showed voltage readings at all of the important circuit points. I made my own chart and proceeded to check every test point under power, measuring the key voltages at every tube and comparing every result to the Sams and RCA sources.

In this photo, testing is underway:

Many voltages can be checked under the chassis, but sometimes it's more convenient to reach things from above. That's where these little test adapters come in handy:

  

Again, the results were encouraging. The TV seemed to be in good health.

Deciding When to Quit

Why do all of this laborious testing, when the TV already seemed to work well? I don't always do a complete resistance and voltage check; testing several key values is usually sufficient, along with observing the TV's performance. But I wanted to treat this set a little differently.

In most TV restorations, I'm aggressive about replacing electrolytic and tubular capacitors. That's unavoidable with a 1940s television if you want it to work at all; 1940s TVs used a lot of parts, compared to newer sets, and some of the capacitors available at the time simply weren't good enough to last for decades. During the 1950s, TVs were simplified and capacitors gradually improved in quality. By the time this set was made, in 1960 or 1961, RCA was using mostly dipped-mylar tubular caps in place of the old wax paper or plastic-coated types.

By this time, I had operated the TV for several hours in total, without any overheating or alarm signs from the electrolytics. The power supply was stable and the set performed surprisingly well. I decided to depart from my usual practice and leave all of the original power-supply electrolytics untouched.

Before doing that, I wanted to convince myself in some detail that that TV really did work as well as it appeared. Hence, the systematic resistance and voltage checks.

As an extra confirmation, I hauled out my EICO 950B capacitor checker and tested the few tubular caps that I had pulled out for replacement. A few were slightly leaky at their full operating voltage, but most of them tested within normal bounds. Ditto for the small electrolytic that I had replaced on the vertical sweep board. Finally, I temporarily disconnected a couple of power-supply electrolytics and tested them.

When those tested OK, as well, I decided it was time to quit fretting and declare victory. As far as I can make out, everything remaining in the TV is working normally.

Final Thoughts

This CTC-11 is a real peach. Its picture quality is at least as good as my first CTC-11, and I think its audio is significantly better. The audio circuitry looks identical, but who knows, perhaps this was a slightly pricier edition with better quality speakers.

In any case, it's a joy to watch, and I have watched this television for many hours in my workshop while I returned to my stubborn CTC-4 project. Now, if I could only find a place to put it in our house! After I figure that out, I'll put the legs back on and take a "now I'm really finished" photo for this article.

©1995-2017 Philip I. Nelson, all rights reserved