by Peter Yanczer

If one mentions mechanical television, most readers will 24 line pix, Felix the Catimmediately have a mental image of a large disk rotating at high speed and providing a dim, small and coarse 24 to 60 line picture. Television began with scanning disks like one patented in Germany by Paul Nipkow in 1884. As work toward developing practical forms of television began in earnest, it was soon became obvious that the scanning holes passed very little light. Even in full sunlight, early television cameras would not operate outdoors. There just wasn't enough light. The same was true at the receiver, where the light source was a flat plate neon lamp. The tiny holes in the disk allowed much less than one percent of the light from the lamp to pass through. It was really "lights out time" when a televisor was switched on.


A bright picture would have been very welcome because it could then be enlarged by projection lenses and any added brightness would have increased the apparent resolution. By increasing the diameter of the Nipkow disk, larger scanning holes could be used. This explains why disks tended to be from two to four feet in diameter. An early improvement over the Nipkow was the lens disk. Lenses were added because they could pass much more Jenkin's lens disklight than the scanning holes. When lenses were used, their optical centers were located in the same place as the scanning holes in a Nipkow disk. John Logie Baird of Scotland had built lens disks as much as eight feet in diameter, ( think about that for a moment! )with 30 lenses as large as bowling balls. He was once almost killed when some lenses came loose while one of these large disks was in operation, throwing everything out of balance. The lenses were flying around the room like large boulders and he wisely took cover.

One good thing about using Nipkow disks was that the receivers Scanning Disk Receiverwere simple and easy to build by the experimenters and many did. Numerous magazine articles were published for those interested in building their own and kits were available too. Most of the radio amateurs of the day could readily "scrounge up" the necessary parts to build one. The one pictured here used an electric fan for the motor and a 16 inch transcription record for the scanning disk. The light shield was a small megaphone.

As photo cell sensitivity and light sources improved, scanning hole size or lens diameters could be reduced. Reducing the disk size resulted in a more45 line lens disk compact scanning assembly. As an example, Western Television of Chicago produced a televisor with a 17 inch aperture disk and a flat plate neon lamp. It provided a 45 line, 1 1/8 by 1 1/2 inch picture. The following year (1931) they developed this new 45 line model (rear view) with an 8 inch diameter lens disk. It provided a much larger and brighter picture, measuring about 4 by 4 inches. The improvement was due to the use of both the lens disk and a more efficient light source, a crater arc neon lamp. This new model included an 8 tube receiver, which the previous model did not and the complete receiver occupied only about half the table space as before.


On to the Mirror Drum