LabGuy's World: The Chief, A 1939 Television Monoscope Project


The monoscope is A TV camera that produces a fixed TV test pattern

       A television monoscope tube is a magic bottle that, when stroked correctly, will make a Dignified Indian Chief appear on yout TV screen! (and some other useful stuff too) I find myself in possession of a pair of authentic RCA monoscope tubes. The 2F21 with the famous Indian Chief test pattern of 1939 and the 1699 station ID card from WEHT, TV channel 50 in Henderson, Kentucky*, 1953. Let's see if we can make these tubes work again. By the way, if you have one of these tubes for sale, feel free to contact me.

       (20190526) Thanks to Greg Stevens for pointing this out to me in the first episode of the YouTube videos. I originally misstated the state as Illinois.

       The monoscope tube is a type of television camera tube. It contains a fixed image, printed on a metal plate, which is read out by a low velocity scanned electron beam in a manner similar to the iconoscope, image orthicon or vidicon tubes. The direct signal from the plate is amplified for use by a normal series of video amplifiers as in any other TV camera.

       The pattern electrode is a thin sheet of aluminum with the image screen printed onto it with a India ink. (Indian ink, anyone? Coincidence? Hmmmm?) The image is very much like a newsprint image in that it contains no actual analog gray values. These are obtained by the frequency produced when the beam scans over the screened printing, in much the same way a playing card used to buzz in our bicycle spokes when we were kids! Think of it as the Class D audio of video! The analog signal is reconstructed by the natural low pass action of the following video amplifier chain.

       During manufacturing, this printed organic ink is baked off at high temperature with the tube filled with hydrogen. After bake off, the tube is evacuated in the normal manner. What remains on the surface of the signal plate is almost perfectly pure carbon. When the scanning beam is striking bare metal, a strong signal is produced on the output. When scanning on the carbonized ink, which is almost an insulator, the electrons are mostly blocked from the metal and weak output will be produced. Many electrons accumulate on the insulator and eventually fly off into the surrounding space. Unchecked, these would fall back to the signal plate and create spurious signals, called shading. Another electrode, a carbon paint coating on the inside of the tube, called the collector, is held to a slightly more positive charge (about 25 to 50 volts) above the signal plate to collect the unwanted electrons.

       A test pattern contains many specialized sub patterns used to measure the performance of a video system. Things like spatial resolution, geometric linearity and signal linearity. With a monoscope, one can accurately align a CRT television monitor. I am not aiming for that type of performance here. This project's first order is to simply display the contents of the tubes in my possession. Improvements can then be introduced incrementally as needed.

       Follow the development of this project on Youtube by visiting: [The Chief videos playlist here]



The nearly completed and fully operational unit in early April 2019

       Work progressed, off and on, on The Chief for two years. I worked my way through many circuits, particularly related to magnetic deflection, which were areas in where my expertise was weak. Thanks to my good friend, Howard Katz, we worked on one issue after another. I refused to move on until I understood each section far better than I had before. This was a very educational time and I am grateful for Howard's incredible patience.

       The following index of stages will walk you through the highlights of the project from start to finish. Go through in order as there is a wonderful surprise at the end. Well worth the time it takes to read through the process. You'll laugh. You'll cry. You'll kiss an hour of your life good bye! You're welcome.

       ~Labguy~


Publicity and other Public Appreciation of The Chief

       Twitter: Tube Time

       Hackaday: Vintage Monoscope Tubes Generate Classic TV Test Patterns Once Again


       If you know of other pages about any of my projects please let me know by dropping me a line at this address (click the picture below for a larger view):



THE CHIEF - PROJECT INDEX:

  • 1. Mechanical Construction. Main chassis and support shielding of the monoscope tube and surprise ending

  • 2. Low and High Voltage Power Supplies. Its not much of a project without the proper voltages

  • 3. Sync Generator, The central source of master system timing

  • 4. Deflection. Horizontal and vertical scanning yoke drivers

  • 5. Video Amplifier Chain. Video signal path from the target plate to output jack

  • 6. References:. What resources were used in the construcion of this device?


  •        This is a completed project. 20190408


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            Created: April 2, 2017 Last updated: May 26, 2019