405 line Mechanical Television

[Geordie McBoyne]

Didn't they attempt to make a mechanical sync pulse generator for 405 lines?
A book was published, "The Story of Scophony" It describes the conception and development of mechanical 405 line TV receivers for home and public viewing. There was also collaboration with Ekco to produce the model ES104.
https://www.radiomuseum.org/r/ekco_scoph...er_es.html
The Scophony TV receiver employed the Jeffree cell which was the device to store the active video part of a scanning line.

Geordie McBoyne.

[Geordie McBoyne]

From the ETF: http://www.earlytelevision.org/yanczer_scoph.html

Geordie McBoyne.

[peter scott]

Yes, they did. Here's their measurement of the AP electronic jitter and their high inertia performance.

   

   

[ppppenguin]

I think the mechanical SPG used methods similar to Hammond tonewheel organs. As the picture shows, it would have very different jitter to an electronic SPG. A good electronic SPG should have extremely low jitter, set by a crystal oscillator plus any added by the divider chains. This should be near zero for modern logic but likely worse for synchornised multivibrators which were used as dividers in the old days.

[Terry]

A semi-mechanical system was proposed by Mullard in the early 60s

A badly worded description in the US Radio-Electronics magazine for October 1961 reads:

"New "Banana" Tube for Color

British Mullard has announced a type of tube using principles altogether different from the shadow mask, Lawrence or others now in development. The tube is a cylinder about 4 inches in diameter, with three equally spaced cylindrical rods running along its length. The screen is simply a strip of phosphor ¼ inch wide and 16 inches long. It is composed of three color phosphors. The beam is "wobbled" to strike the desired phosphor at any point along its scan. The gun is mounted at one end of the tube and the beam projected parallel to the phosphor strip, being bent down to it by a "bowing, magnet" that acts as the horizontal sweep. Vertical sweep is mechanical, by rotating the tube at about 1,000 rpm. Light from the phosphor strip is projected through cylindrical lenses to form the image on a mirror, from which it is viewed. Still in an early experimental stage, the tube is not far enough developed to make any predictions as to its ultimate feasibility possible."

Had I not remembered the original illustrated proposal published by Mullard (not available on line as far as I can tell) I would have had a clue as to what the Yanks were talking about!

'The tube is a cylinder' right at the beginning turns the rest into gobbledegook as it comprised both a cylinder - the mechanical part - and a tube - the electronic part.

The description of the banana tube is reasonable but it is the mechanical part that is confusing. The tube was at the centre of a cylinder which had the cylindrical rods in it. These were the cylindrical lenses referred to.

The cylinder rotated at a third of field rate, so 999.6 rpm for 50 Hz systems or 1200 rpm for 60 Hz systems.

Because of the rotating lenses, the mirror was parabolic rather than the plane mirror used in pre-war sets.

I don't recall a diameter for the tube but the Mullard drawing indicated a cylinder much bigger than 4 inches!

How they proposed to stop the phosphor strips from burning was not, as far as I recall, stated but must have been a major problem.

[Terry]

Had I not remembered the original illustrated proposal published by Mullard (not available on line as far as I can tell) I would have had a clue as to what the Yanks were talking about!

Oops! That should, of course, have said " I wouldn't have had a clue ..."

[davegsm82]

I can't help but note that it says the 'Light' is modulated by the Quartz relay, doesn't mention actual control of the filament current, could they be shining light at the crystal and using its resultant deformation under electrical tension (from the output of the video demodulator valve) to reflect the light up or down (or whatever orientation) to change it's intensity? it actually all sounds fairly feasible.

Dave.

[peter scott]