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Mullard 25" rectangular colour CRT available in 1965.

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Nuvistor
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This was reported in the Magazine Radio Electronics Oct 1961 page 6. If it had been the April issue I could have understood it.

http://www.americanradiohistory.com/Archive-Radio-Electronics/60s/1961/Radio-Electronics-1961-10.pdf

It would have been interesting fixing tv's fitted with one of these.

Quote.

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 simply a strip of phosphor 14 inch wide and 16 inches long. It is com- posed 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 pro- jected 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.

 

Frank

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Posted : 03/12/2016 9:25 pm
ntscuser
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nuvistor said
From memory the first CRT's used in the U.K. I was told that the shadow mask was more suited for 525 line sets and moire patterns were more pronounced. The A56-120X shadow mask was designed for 625 line sets, giving better pictures and less moire patterns.

How true that information is I cannot say, could be salesman talk or it could have come from the technical support people, too long ago.

It's true. I read quite recently (but can't remember where) the early rectangular shadowmask tubes had a vertical resolution of only 480 lines whereas the later ones could manage 575 lines. The horizontal resolution was slightly increased too.

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Posted : 03/12/2016 10:48 pm
Nuvistor
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ntscuser said

 

It's true. I read quite recently (but can't remember where) the early rectangular shadowmask tubes had a vertical resolution of only 480 lines whereas the later ones could manage 575 lines. The horizontal resolution was slightly increased too.  

There is a link in post #9 to a Mullard leaflet, it does not mention the resolution but I think that will be what it will be referring to.

That lead on to a brilliant post from Till about Telefunken and the A56-120X.

The Hansard report gives a good indication to the state of the UK TV and CRT industry in the middle 70's. Post #15.

I was a young man with a family to support at that time, my priority was paying the bills, the wider implications of the industry was not thought about. Looking back now I can see how bad a shape the UK TV industry was in. 

Frank

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Posted : 04/12/2016 10:30 am
malcscott
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I remember the quick heat A56-120X. Rediffusion aquired a batch of these which were fitted into the refurbished RT529/22, (Bush A823) This set (RT559/22) was fitted with a 6 button varicap tuner and the quick heat crt. The picture would appear within less than 5 seconds and the degause could be seen in operation. Anyone remember the A55-14X ? I think that was the number. It had rounded corners, Malc.

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Posted : 04/12/2016 10:45 am
Nuvistor
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Hi Malc,

Was the quick heat A56-120X directly heated or did it have a cathode? I don't remember them myself but that's nothing to go off.

Nothing about the A55-14X, again we only had a small range of sets, ITT, RBM, Pye, Toshiba and Hitachi. I suppose that's enough for a small shop.

Plus the fact it's 40 years ago and my working life was computing after the late 70's.

Frank

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Posted : 04/12/2016 11:14 am
Till Eulenspiegel
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Hi Malc, The quick heat A56-120X will have the low heater consumption heaters similar to later versions of the 110degree Philips/Mullard A56-410X, the heater current was reduced from 0.9 to 0.73amps.  The fact the quick heat A56-120X had a different gun assembly should have meant the type designation should been changed to say, A56-210X.   Perhaps Rediffusion had commissioned Mullard to make the special A56-120X.

BRC was lumbered with that awful round corner 22" A55-14X because Thorn Colour Tubes Ltd. was not privy to the Mullard/Philips patent for the square corner A56-120X although European company Telefunken was. 

Hi Frank,  I never came across the quick heat Hitachi CRT, however I do know the tube did have three directly heated cathodes, just like a battery radio valve.  The meant that three heater windings were added to the line output transformer, not nice if you think about it because of the added capacitances could spoil the HF response of the RGB amplifiers. Anyway, the tube was short lived and Hitachi replaced the quick heat tube  with a conventional indirectly heated tube.

I can agree with you about the later Japanese TVs, by the late eighties the sets were certainly not as reliable as the super reliable imported sets which were made in the seventies.  Some time ago I visited a customer who owned an early Mitsubishi Blue Diamond TV. This set had never had any service work done to it in twenty-six years. An easy repair but we had to take it outside to blow out the thick layer of dust. Late production Mitsi's weren't very good though.

Till Eulenspiegel. 

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Topic starter Posted : 04/12/2016 1:18 pm
Till Eulenspiegel
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Hi Malc,

             Was the refurbished RT529/22 still housed in the larger Bush CTV184 style of cabinet? Also, was the varicap tuner and station selector buttons taken from other Rediffusion models, no point buying in parts from Rank-Bush-Murphy when you can make your own bits.

Till Eulenspiegel.

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Topic starter Posted : 04/12/2016 1:26 pm
Nuvistor
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Hi Till,

That's an interesting thought about reduced HF response. I don't remember it being a problem, there were chokes in each heater to isolate the LOPTX, and if it had been really poor we would not have sold them.

However, the UK system had one of the higher video bandwidths, Germany had about half a meg less and the NTSC system going on for one and a half megs less. It's possible that the designers thought that they could get away with perhaps 4.5 to 5Mhz. There would be a trap for 4.4Mhz in the video anyway.

Frank

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Posted : 04/12/2016 1:40 pm
malcscott
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Hi David, the RT559/22 was fitted with a new cabinet with smart teak coloured veneer and the varicap tuner assy was a left over from the MK13 mono aerial sets. Every modification possible was carried out on these sets and they gave a good account for themselves. I think less than 100 were produced, they rented very well as de- controled sets, Malc.

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Posted : 04/12/2016 3:26 pm
ntscuser
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If you think about it, it would have been impossible to to display 819-lines on a shadowmask tube which may be why the French abandoned it in favour of 625-lines?

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Posted : 04/12/2016 6:11 pm
Terry
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Posted by: Nuvistor

This was reported in the Magazine Radio Electronics Oct 1961 page 6. If it had been the April issue I could have understood it.

It would have been interesting fixing tv's fitted with one of these.

Quote.

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 simply a strip of phosphor 14 inch wide and 16 inches long. It is com- posed 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 pro- jected 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.

Wow! This post is 12 years old!

Funnily enough, I came across article this and posted it over at GVR in a thread about mechanically scanned 405-line pictures. As I remembered that the banana tube had a mechanical component, it seemed appropriate to mention it.

I wonder, though, how many understood exactly how it worked because, quite frankly, that article is rubbish! This is what I said ao GVR:

Had I not remembered the original illustrated proposal published by Mullard (not available on line as far as I can tell) I wouldn't 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.

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Posted : 30/06/2018 11:49 am
Nuvistor
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No I didn’t really understand it, that’s why the comment about April. ? 

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Posted : 30/06/2018 12:06 pm
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