RCA CTC-7 Color Television (1958)

              

              

This RCA CTC-7 color television makes a fine companion to my other two "roundies," the 1954 CT-100 and a 1962 CTC-11. It was built in 1958, four years after the path breaking CT-100 and four years before the CTC-11.

Meet the RCA CTC-7

RCA offered its CTC-7 color TVs with many cabinet styles, colors, and options. My set has a mahogany Pensbury cabinet. This 1958 ad shows a Pensbury with a blonde finish.

The ten (!) other cabinet styles were named Abington, Anderson, Brandywine, Grenoble, Meredith, Sanford, Southbridge, Townsend, Whitmore, and Worthington. Remote control and UHF tuning were extra-cost options.

Color TVs were very expensive in 1958. My CTC-7 in a Pensbury cabinet, with manual VHF tuner, sold for $795. By comparison, $2300 would buy you a new 1958 Chevrolet Biscayne auto. As with cars, financing plans were offered to let you pay for your new color TV over a period of years.

The model number of my CTC-7 is 21-CD-8910M, seen on the back cover:

RCA sold the CTC-7 under 46 different model numbers. All of them start with 21-C, which means 21-inch color television. The 8910 identifies my cabinet and M means manual tuning. Optional UHF tuners and remote controls were denoted by U and R in model numbers.

Scoring a Seven

Finding this desirable early color set was a stroke of luck. I happened to notice the seller's ad in the local craigslist only minutes after it was posted. The asking price was $55, quite a bargain. A quick phone call confirmed that it was a model CTC-7 and soon I was speeding down the freeway with cash in my jeans.

The seller met me in front of a big old apartment building. As we walked to the door, I looked up and joked, "I hope you're not gonna tell me it's located on the top floor." Just my luck—it was! However, the building had an elevator and the seller had a sturdy, padded moving dolly, so getting it down to street level was no problem.

Muscling this heavy console into the back of my little SUV was trickier. The top of the TV only cleared the truck's ceiling by about half an inch. When I got home, all of my helpers were AWOL, so I had to leave it in the truck overnight.

First Look

By the next morning, the CTC-7 was safely stowed in the garage and I could get a better look at my new find. The cabinet was in excellent shape. I hauled out my trusty panther lamp to take an "as found" photo.

The Pensbury cabinet is a quality piece of work. The lacquer finish is deep and lustrous and much of the cabinet is solid wood rather than veneer. Here are two rear views:

The interior was dusty but not caked with layers of old cooking grease and tobacco tar, as many old TVs are. Cleanup will be easy. Like my CTC-11, the chassis stands vertically along one side with a small convergence board on the top rear edge.

In this photo you'll see a welcome feature: triple speakers, with a big woofer and two angle-mounted tweeters. This deluxe CTC-7 has high-fidelity audio!

Next is a view of the knobs and control cover on the side of the cabinet. Notice the wear circle around the fine tuner. Early color TVs demanded careful fine tuning and this set was no exception. It won't be difficult to touch up this area. Behind a small tilt panel are the less often used controls: Tone, Contrast, Vertical, and Horizontal.

  

A rubber stamp identifies this as a CTC-7AC. Stamped into the chassis metal is serial number B5018582. The same number appears on a tag on the picture tube shield.

While cleaning up, I found a repair tag dated 1977 (I blurred out the owner's name and address to protect her privacy). No work is listed, so perhaps the serviceman lost this tag and filled out another one, or possibly the owners decided not to repair the set after they got a price estimate.

Electronic Design

The CTC-7 design clearly evolved from the seminal CT-100, yet it shares many features with later color sets like my CTC-11. Here is the unrestored chassis:

The overall CTC-7 chassis layout is very similar to the CT-100. Major components such as the tuner and power supplies are in the same places, although some sections have migrated onto printed circuit boards.

The chassis is mounted sideways rather than flat in the cabinet. This simple change from the CT-100 cost little to implement and it gave the customer an obvious ergonomic benefit. Flipping the chassis on its side moved the tuner and other user controls near the top of the cabinet rather than under the screen. The same configuration was carried forward in my CTC-11 and many other televisions.

This diagram shows the chassis layout in detail (click for an expanded view):

Here is a list of the CTC-7's 24 tubes:

Tube Type Function
V1 6BZ6 1st Video IF Amplifier
V2 6BZ6 2nd Video IF Amplifier
V3 6AW8A 3rd Video IF / Sync. Sep.
V4 6AW8A Video Amp. / AGC Keying
V5 12BY7A Video Output
V6 6U8A Audio IF Amp. / Noise Inverter
V7 6DT6 Audio Detector
V8 6AQ5A Audio Output
V9 6CG7 Sync. Amp. / Vert. Mult.
V10 6AQ5A Vert. Mult. / Vert. Output
V11 6CG7 Horizontal AFC / Horiz. Osc.
V12 6DQ5 Horizontal Output
V13 6AU4GTA Damper
V14 3A3 High Voltage Rectifier
V15 1V2 Focus Rectifier
V16 6BK4 High Voltage Regulator
V17 6U8A 1st Chroma Band. / Color Killer
V18 6AW8A 2nd Chroma Band. / Burst Amp.
V19 6BN8 Chroma Sync. Phase Detector
V20 6U8A Chroma Ref. Osc. & Control
V21 12AZ7 X Demodulator / Z Demod.
V22 12BH7A R-Y Amplifier / B-Y Amplifier
V23 6CG7 G-Y Amp. / Horiz. Blank. Amp.
V24 21CYP22 Picture Tube
V201 6BC8 RF Amplifier
V202 6CQ8 Mixer / Oscillator

The CTC-7 uses solid state audio and video detectors as well as rectifiers. My set has the VHF tuner with two tubes. The optional UHF/VHF tuner had three tubes and a crystal mixer. Two versions of remote control were offered, using either eight or nine tubes on a separate chassis. Transistors were employed in the wireless remote transmitters.

My TV is a CTC-7AC. The "original recipe" CTC-7 (no AC) had some significant differences, including two rectifier tubes.

In my article on CT-100 Electronic Design, I described the so-called I-Q method of color demodulation and noted that some later receivers used a simpler scheme known as Z-X. The CTC-7 uses Z-X demodulation, as does my newer CTC-11.

The Sams service manual for this TV is set 433, folder 2. This article refers to components by their Sams part numbers.

Another essential reference for CTC-7 owners is the RCA Television Service Clinic manual. It's fifty pages long and written for engineers and servicemen who attended RCA technical lectures. In addition to the usual service information, it discusses the theory of operation for every major circuit.

Click the icon below to download the complete RCA manual (a 21-megabyte PDF file):

The RCA manual depicts the original CTC-7 design with dual rectifier tubes and other differences from later versions. For version-specific information, use the Sams manual.

Electronic Restoration

Only days after finding this TV, I got my wife a Philco Miss America console as a Valentine's present. I spent two weeks restoring that TV and writing an article about it. Finally, I was able to turn my attention to the CTC-7.

Checking and Cleaning Tubes

A critical question for every early color TV is the condition of its picture tube. If this CRT is a dud, I could spend much more than $55 finding a good one to replace it!

My Sencore CR70 showed that this tube has strong emission. This photo shows the test result for the Red gun; the Blue and Green guns also passed with flying colors.

A tedious but important initial chore is to test all 23 of the small tubes and clean their pins. As frequently happens, almost all of them were good. Only the 6DT6 audio demodulator looked too weak to work properly.

A side benefit of methodical tube testing is that you can clean the chassis as you go and inspect each area for obvious trouble signs. Everything looked nice, even the precious flyback transformer, which showed no dripping wax or evidence of overheating.

Removing the Chassis

Removing the chassis is straightforward, following the directions in the Sams manual. The knobs on my CTC-7 were stuck on very tightly. At first, I was unable to pull any of them off. Rather than break them or gouge the cabinet by trying to pry them off, I heated each one gently with a heat gun. This expanded the plastic enough to let me slowly ease it off.

On many TVs, the high-voltage anode lead is detachable at the picture tube bell. On this set, you detach the other end of the lead from a tube socket inside the high-voltage cage. After swiveling the round cage cover open, you pull the lead straight out.

In this photo, I have removed the knobs and chassis mounting bolts and disconnected all of the necessary cables and leads from the chassis. The little parts are bagged for safekeeping and all wires are safely stowed.

Notice the red anode lead lying next to the high-voltage cage. Its other end remains attached to the picture tube.

Kneeling behind the cabinet, I slid out the heavy chassis. Here is my first close look at this set, which I'll come to know well in the upcoming project.

Let's note some major landmarks. In a black enameled box at upper left is the massive power transformer. Three big cans immediately to its right contain the electrolytic capacitors for the power supply. At upper right is the shielded tuner.

At the bottom is the big, black high-voltage compartment. In the center of the chassis we see four of the CTC-7's six printed circuit boards: Horizontal, Vertical/Sync, Audio/Noise inverter, Video/AGC. The convergence board is still mounted on the cabinet above the neck of the picture tube and the video IF board is concealed in a shield on the opposite side of the chassis.

Restuffing Electrolytic Capacitor Cans on Undisturbed Bases

The CTC-7's primary electrolytic capacitors are contained in three cans, like my CTC-11. I'll "restuff" them by putting new caps in the original cans. It's possible to put the new electrolytics in the narrow channel under the cans, as I did with my CTC-11, but that's a very tight fit.

The first photo shows three new electrolytics that will go in the big aluminum can. Notice the narrow board placed under the chassis. When you lay a CTC-7 chassis flat, provide a support to keep its weight off the control shafts.

I masked the chassis to keep dirt out. Sawing the can takes only a few minutes.

  

The second can has a cardboard cover. I was able to pull it off after softening the tarry adhesive with a heat gun. The adhesive will clean up easily with mineral spirits. If you're in a hurry, you could leave the cover in place and saw through it, but this way the restuffed can will look completely original.

A cardboard cover is used to insulate a can whose exterior has a negative potential that is "floating," meaning that it is not connected to the chassis and thus presents a shock hazard. As seen in the photo, this can is mounted on a nonconductive base to isolate it from the chassis. My replacement capacitor will have no electrical connection to the can, but I'll put the cardboard cover back on to preserve its original appearance.

Let's proceed to the third can. For this one, I'll use a hacksaw blade because the hobby knife is too wide to fit the narrow space. Notice how I have drawn little temporary registration marks across the place where I'm making the cut. These will allow me to glue the can back exactly as before. It's hard to make an absolutely symmetrical cut. If I match up the marks, any wobbly edges will match up, too, and make a neat joint.

It's not always practical to saw a can. If it's mounted in the middle of a chassis and surrounded by other components, there may be no room to fit a saw blade or Dremel tool. In that case, you can either detach the can from underneath and restuff it, or leave the can in place (disconnected, of course) and install the new caps under the chassis. Those other methods are described in my capacitor replacement article.

The next photo shows why "re-forming" old electrolytics is often a losing game. The innards of the first two cans are not terribly dried out, but the third one is a complete fossil. The paste electrolyte dried and shrank long ago. In this condition, the capacitor may even have shorted and overheated, very dangerous for a power transformer.

Removing the cans' old contents is also done with a heat gun. Drive a big wood screw into the innards, get the can good and hot (wear gloves!) and then pull everything out with a pliers. You can use mineral spirits to clean residue inside the empty cans, if you like, but I don't get too obsessive about that. Nobody will ever look inside them again!

Next, I have drilled tiny holes in each base for the new capacitor leads, one hole for each positive lead and an extra for the shared negative lead. The holes are located inside the terminals (nearer the can center) rather than outside. This avoids running into outward-radiating leads under the chassis.

Behind the empty cans you can see my hand-drawn cheat sheet. It shows the can bases from above and below, indicating the location of every lead and the value (and Sams part number) of each capacitor. This took a few extra minutes, but it let me do the final hookup quickly, without a lot of head scratching and flipping back and forth between my work and the schematic.

In the following photo, I'm two-thirds finished. The middle can needs only one capacitor. In the first can, I have installed three, but the little low-voltage cap is obscured behind the black tuner lead.

The third can is too small to contain all three capacitors, so this assembly has only two caps. Insulate the hot leads carefully to avoid any chance of short circuits. Your assemblies don't have to look beautiful as long as they're safe and functional.

Finally, here's the orphan electrolytic that wouldn't fit in the third can, installed in the cramped space under the chassis. If you look closely, you can see some of the new cap leads snaking down through holes to be soldered to the old terminals.

A great advantage of this method is that it doesn't disturb the original electrolytic wiring. Look at all of the wires in the previous photo. When I restored my CTC-11s, all of the new electrolytics had to go into that narrow channel. It was hard to fit everything in and avoid mangling the old leads.

We're done! The new electrolytics are installed and the cans are polished and ready to put back on.

The new electrolytics are operational and I can proceed with restoring the electronics. When I get around to cosmetics, I'll glue the cans back on using JB Weld. The grey epoxy is a good color match for the aluminum and after I clean the finished joint, it will be almost invisible.

First Power-Up and Raster

With new filters in the power supply, it's safe to power up the television under controlled conditions. I'll keep a close eye on its power consumption with a wattmeter and use a variac to gradually increase the supply voltage.

When you switch on a CTC-7, you'll notice a delay before any sound or video is produced. The TV has a thermal switch, shown below. The switch lies between the power source and the B+ circuits. When you turn on the TV, power is supplied immediately to the filament circuits, allowing the tubes to warm up. Then the thermal switch kicks in and you have audio and video. The "soft start" is provided to prolong the life of tubes and other components, similar to the delay circuit in my DuMont RA-103.

I haven't taken the switch apart, but I suspect it's similar to a toaster switch with a bi-metallic strip, a much simpler alternative to DuMont's over-engineered delay circuit.

The first power-up was encouraging. As the next photo shows, the TV is producing a raster (screen illumination) with full horizontal deflection, although vertical deflection is insufficient. Sound from the speakers indicates life in the audio section and colored snow on the screen suggests that the color sections work. There is no hint of an image and the speakers produce only static, so clearly the signal is not getting through.

In the Good News department, a stable raster indicates health in the picture tube and flyback transformer. Either of those components would expensive to replace, if you could find one at all.

Curing the No-Signal Condition

Let's begin with something easy. Faced with a no-signal condition, you could try various strategies. One would be to connect a test signal at the antenna terminals and then walk forward along the signal path, tracing key points with an oscilloscope until the signal disappears. You could also start at the other end, injecting a signal at a forward point such as the video output tube; if a good image appeared there, you could walk backward along the path until, again, you found a stage that wouldn't pass a signal.

Before getting fancy, however, let's check the obvious. Although I had previously tested all of the small tubes, that's no guarantee that one of them hadn't just croaked after its first exposure to working voltage in decades.

Sure enough, tube V201, the 6BC8 RF amplifier, had failed. I substituted an equivalent 6BZ7 from my tube stash and powered up again.

Big improvement! The audio was excellent and I got a coherent (well, semi-coherent) image for the first time.

Vertical deflection is still lacking, but we already knew that. In addition, I can now see that the horizontal frequency is wrong. The image is repeated horizontally and overlapped. I was unable to correct this merely by turning the horizontal hold control, although I could make it stabilize, mostly.

The horizontal oscillator is running near a multiple or fraction of the correct frequency (15734.264 Hz). The hold circuit tries to lock onto that, keeping things somewhat stable, but the image is incorrect.

Recapping the Horizontal Deflection Board

Of all circuits in a television, the sweep circuits, and particularly the horizontal, are the most failure-prone. They require precise timing, so the mere aging of components, especially capacitors, can make problems.

We can see at a glance that the horizontal section had issues in the past. I have circled in yellow the capacitors most likely to fail. Only two of them are original. The other three (one aqua and two black with orange markings) are replacements.

     

Even though the replacements are somewhat newer, they are still the old, unreliable plastic-coated paper type, so I replaced all five caps, as seen in the third photo. The big uppermost cap had an unusual value (.0027 mfd/1 KV), so I piggybacked caps to make one that will work.

Yes, Dorothy, that's a color TV, all right!

I see real color for the first time and the horizontal problem is cured. The picture is rock solid and I can't make it go out of sync, even by turning the horizontal hold all the way in either direction.

Recapping the Vertical Deflection Board

It doesn't take a Wizard to tell me where to go next. The vertical/sync board has more caps than the horizontal board, but the result of replacing them is no less satisfying.

           

We have full deflection and the vertical hold is stable.

This project has gone smoothly so far, but we're still a long way from Kansas.

Recapping the Main Chassis

Although a number of the original "maroon drop" capacitors seem to be holding up, I decided to replace the rest of them. Those on the sweep boards had suffered a non-trivial failure rate, and there's nothing I hate more than "fixing" a TV, only to haul it back into the shop a week or two later because some marginal component finally gave out.

The remaining small capacitors were scattered around the chassis, including a couple of boards that I hadn't visited, but the majority were concentrated in the color sections. Here are before and after photos:

  

Mid-Course Status Check

My CTC-7 is shaping up! Here's a snapshot of the screen after I finished recapping:

The picture is pretty watchable and the audio is fantastic. (Why did so many TV companies skimp on audio?) The television is stable and the voltages at key points are normal.

Click the icon below to view a six-second video clip. Unfortunately, the pinhead-size microphone in my camera can't do justice to the audio.

It's a testament to RCA engineering that this 53-year old TV looks as good as it does, given that I haven't yet done any of the setup procedures that are standard for every vintage color set. Those include degaussing, purity, grayscale, and—my nemesis in other "roundie" restorations—static and dynamic convergence.

In fact, apart from taking a quick stab at vertical height and linearity, I haven't even gotten around to the screen geometry adjustments that normally precede color setup.

Some performance adjustments remain, too. In an early check, I found the high voltage somewhat low, around 18 KV rather than the 20+ KV given in the manual. This may explain why the picture brightness isn't outstanding, even though the CRT's emission looks strong on the tester.

Getting the high voltage right is a multi-step procedure that includes viewing the horizontal waveform on an oscilloscope and adjusting the horizontal output tube's cathode current to the minimum level that produces adequate HV. Setting the HOT cathode current is important to avoid overloading the flyback transformer, which could cause an expensive meltdown.

Other adjustments include the color killer, AGC . . . and the list goes on.

Tuner cleaning and lubrication is also on my list. The tuner works, but with scratchiness that typically indicates oxidation on its contacts. DeOxit and Q-tips should clear that up.

To Be Continued . . .

That's as far as I've gotten at this writing (March, 2011). I'll update this article after I've made more progress.

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