Early Electronic Television
Westinghouse WRT-703 Restoration
This set is a 12 inch mirror in lid model with a radio. The chassis were made by RCA, are identical to the TRK-12. Here is technical information.
Cabinet. (pictures) The cabinet is in fair condition, with many scratches and peeling veneer. It will need to be refinished.
Chassis. There are four chassis: TV power supply, TV receiver, radio power supply, and AM/SW Radio. Each will be cleaned with water and a mild detergent using soft brushes to get into small places. Then, all paper capacitors will be replaced with modern ones (see the procedure for this). Each electrolytic capacitor will be tested for leakage and capacity. If bad, new electrolytics will be installed inside the old ones.
TV Power Supply Chassis: (pictures) This chassis is in good condition with no rust. It contains the low voltage supplies for the TV chassis and the high voltage supply for the CRT. The HV (EHT) transformer was bad. I had a replica made by Ed Dinning in England to fit inside the old can.
First, the old transformer had to be removed by heating the can with a heat gun to melt the tar. Then, the old transformer was removed. Mineral spirits were used to clean the remaining tar. Then, the can was repainted, and the new transformer was installed.
TV Receiver Chassis: (pictures) This chassis is in good condition. It contains the RF, IF, video, audio and sweep circuits. This chassis is identical to the RCA TRK-12, except that there is no serial number stamped into it. Ours is in excellent condition, with no rust.
At one time it may have had a separate RF preamplifier, probably added after the war. Three wires ar soldered under the chassis, for 6.3 volts, ground, and B+ (HT). The wire is the type that was commonly used during World War Two.
I finished rebuilding the capacitors today, and applied power. The first problem is the vertical (frame) output transformer, which is open. Chuck Azzalina used one from a GE 800 as a replacement. I'll do that for now, but will get the transformer rewound. The horizontal (line) sweep is fine.
I set the local oscillator to 74 mHz and attempted to get 12.75 mHz IF at the video detector, but there was no trace of it. I discovered that the AGC voltage was -8, and did not change with signal level. I changed the 6F8 AGC tube (valve), the voltage dropped to -2.8, and I got a signal at the detector. I checked the video output and discovered that the waveform was badly distorted. Reducing the RF input to the set solved the problem, but there may still be something wrong with the AGC. Both of the 6F8 AGC tubes (valves) I have are bad, so I suspect that is the problem. For now I am operating the set with an external bias supply. I installed a good 6F8, but that didn't solve the problem. It turns out that I had installed a new electrolytic capacitor backwards inside an old shell. The AGC now works perfectly.
The image (just a line now until I get the vertical output transformer replaced) on the CRT is bright and nicely focused.
I borrowed a vertical (frame) output transformer from another set until I get the old one rewound. The vertical sweep is now fine.
However, the width is marginal. When I turn the width control up enough to fill the screen I get slight distortions in the horizontal sync. The best way to describe this is that if you look at what should be a vertical line in the picture it isn't vertical, but has a jagged appearance. When you reduce the width the picture is normal.Our RCA TRK-12 had the same problem.
I think it is due to the fact that these sets were designed for 441 lines (13,320 Hz) sweep, and operating them at 15,750 Hz makes the horizontal (line) sweep work too hard. I've found that putting a .005 or .01 from the plates of the damper tube to ground will increase the width so that you can turn down the width control enough to eliminate the distortion.
The picture is now stable and clear, and the sound section works. Now that I can see the entire raster, I realize that the tube is a little weak. However, the tube in our TRK-12 started out that way, and after a few hours of use it became much brighter.
Radio Power Supply Chassis: (pictures) This chassis is in good condition. It contains the power transformer and rectifier for the AM/SW radio.
The electrolytic is a wet type, and is overheating, so I will rebuild it.
AM/SW Radio: (pictures) This chassis is in good condition. It contains a high quality AM/Short Wave radio.
After rebuilding all the paper capacitors, the radio works perfectly.