29-06-2018, 06:52 PM
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.
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.
