Off-screen photo from Cliff's friend's Colordaptor
Cliff's scope tells the story. Top: Blue tritch plate waveform. Bottom: Servo phase detector waveform. |
Color Wheel SyncJim: Is that Wizard of Oz picture you sent a Col-R-Tel shot, or a Colordaptor shot? Cliff: That shot is the Colordaptor making a color picture on the 12-inch Philco screen. The Philco is a model 50T. The source video is a still-framed DVD playback into a VCR. The VCR's channel-4 modulator feeds the Philco tuner. Jim: What type of wheel wedge pickup do you use? Two magnetic pickup coils, as on your solid-state Col-R-Tel? Cliff: I only have one working color wheel (my original Col-R-Tel wheel). The wheel is missing the printed circuit switch and brushes. Without those parts, I had no way to make the wheel work with Col-R-Tel. I decided to use the Col-R-Tel wheel to test Colordaptor. Inside the wheel hub, I added two small magnets. My magnet sensor is the head from an audio cassette deck. To position the magnets and tape head, I followed instructions in the Colordaptor article. The pulse occurs just as the blue filter starts traveling down across the picture tube. With the Colordaptor servo circuit, this setup works perfectly. Colordaptor vs. Col-R-TelJim: How does Colordaptor compare to Col-R-Tel? |
Cliff: Hmm. Not an easy question to answer. Remember that the Col-R-Tel is a manufactured product. Colordaptor is at best a kit of essential parts. At worst, Colordaptor's a 10-page how-to article. One column of corrections came out three months later. Colordaptor is more complex than Col-R-Tel. During alignment, Colordaptor's more touchy than Col-R-Tel. Colordaptor setup is more difficult, too.
The picture quality of the two units is similar. Col-R-Tel's hue and color adjustments work better. Col-R-Tel adjustments are more reliable than Colordaptor adjustments.
The scope shot shows the blue tritch plate waveform. Below that trace is the voltage ramp output of the phase detector. This ramp drives the grid of the 6AQ5 wheel servo.
Delay Lines
Jim: What type of delay lines did you settle on?
Cliff: For testing and experiments, I use 75-ohm, broadcast-quality delay lines. I got these lines on eBay. To my complete surprise, all the lines worked! I haven't attempted using 75-ohm video cable delay lines. These entail coiling 500 or 600 feet of cable under the TV set!
All 75-ohm delay lines require standard video distribution amplifiers. The amplifiers drive the lines with a 75-ohm sending and receiving impedance. This impedance prevents reflections and ghosts. I designed a 75-ohm output driver amplifier with a very high-impedance input. This amplifier serves as a buffer between the Philco TV and the delay line. With this amplifier, video from the Philco drives a delay line without loading the detector.
For good pictures, Colordaptor needs some 1.2 microseconds of delay in the TV video path. The TV in a Col-R-Tel installation needs 800 nanoseconds of delay.
I'm trying to find some vintage delay lines like those from 1960s TVs. The 75-ohm delays require solid-state interface circuitry. The solid-state buffers are from the wrong period. For that reason, I don't want to install the 75-ohm delays permanently. If I can't find some old-style delay lines, I'll try building some. I'll refer to the excellent instructions from the Col-R- Tel area of your Web site.
Jim.Thanks for the compliment, Cliff. The delay line page was a lot of work and a lot of fun. Here's a link to it. Click... Wind Delay Lines
If anyone has a delay line for Cliff, drop me a line. My contact data is at the bottom of this page. I'll connect you with Cliff, and you two can cut a deal.
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