INNOVATIVE
MECHANICAL TELEVISION
by
Peter Yanczer
If one
mentions mechanical television, most readers will 
immediately
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.
NIPKOW DISK
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 
light
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 
were
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 more
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.