Early Color Television
The Colordaptor kit consists of three parts: the television receiver, the converter chassis, and the color wheel.
The Receiver: The receiver is a standard early 50s 12 inch black and white TV set. It is modified in several ways:
- A preamplifier is mounted on the chassis to boost the output from the video detector to feed signal to the converter chassis
- A connection is made to the vertical and horizontal sweep sections to provide timing signals for the converter chassis
- A delay line is added in the video amplifier circuit
- A resistor is added in series with the picture tube grid to allow insertion of color information from the converter chassis.
Fortunately, the capacitors had been replaced by the previous owner, and the set works perfectly.
The Color Wheel: (pictures). The color wheel is made of 6 color filters (2 each of red, green and blue), and is about 4 feet in diameter. It is connected to a small drive motor with a belt. The wheel is mounted inside a wooden and cardboard housing.
A magnetic sensor sends one pulse per revolution of the wheel to the Converter Chassis.
The color wheel appears to work perfectly.
The Converter Chassis: This is a home made chassis with 7 tubes on it. It takes the chroma information from the Receiver chassis and derives red, blue and green video information. Using the vertical sweep pulse, it alternately applies the R, G and B video to the picture tube, changing the color every frame.
A servo circuit takes pulses from the color wheel magnetic sensor and compares them to the vertical scan rate, adjusting the color wheel motor speed to keep the wheel turning in synchronization with the vertical rate. A phase adjustment locks make sure the proper color filter is in front of the picture tube as that color's video information is displayed.
I have started to work my way through the circuitry. The first problem is with the "triitch", a three way electronic stepping switch that routes the color information to the picture tube. After finding several bad resistors, I got the switch to step properly. However, it won't work with the vertical pulse as the switching signal. All the voltages and waveforms appear correct. The switch now steps properly, but only by modifying the circuit somewhat. I will explore this later.
Next, I connected the chassis to the wheel and tried to get a picture. I was successful, but much remains to be done. The motor sync is very touchy, and the motor doesn't rotate fast enough. I had to add a transformer to boost the AC voltage to the motor. And, the color is very smeared, indicating that the chroma amplifier alignment is wrong.
After replacing a couple of capacitors the color wheel sync is better, but still touchy. It could be related to the fact that the motor doesn't turn the wheel quite fast enough.
The set came with an extra motor, which is 1650 rpm instead of the 1500 rpm one on the wheel. I have checked the ratio of the pulleys used in driving the wheel, and 1500 rpm doesn't turn the wheel fast enough. So, I am in the process of replacing the motor. I am beginning to wonder if this unit worked when it was built.
Today I talked with the daughter and son in law of the engineer who built the Colordaptor. They both assure me that it did work, but that the sync was very touchy. They describe the picture as "you could tell it was color, but it wasn't very clear".
I tried the new motor today, but it isn't large enough to turn the wheel. So, I'm back to the original motor. The motor turns at 1500 rpm, the drive wheels are 2 inches in diameter on the motor and 5 inches in diameter on the wheel. The speed of the wheel therefore should be 600 rpm. It turns almost that fast, but not quite. It probably did turn fast enough 48 years ago! I've added a 24 vac transformer in series with the motor to boost the speed.
I also did an alignment of the color circuitry, and made some improvement to the color smearing. I now have a reasonably good color picture which holds more or less still for minutes at a time.
When I moved the set to the museum, the wheel turned at too high a speed. I removed the 24 vac transformer, and it worked normally. The AC voltage at the museum is about 2 volts higher than at my shop, and apparently that was enough to bring the wheel speed up. The adaptor now works nicely, though the color is not very vivid. The wheel sync works well.