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Blog posts of '2013' 'April'

GLASS ENGINEERING FOR CATHODE RAY TUBE MANUFACTURE (ii)

Today we'll look at the CRT neck production and their joining to the cone to make a complete CRT bulb.  The neck was the only glass part of the CRT to be made at Mullard Blackburn as the site glass plant was well versed in dealing with tubing which was also used to manufacture valve envelopes as well as tube necks.  In the glass making machine, molten glass flows on the outer surface of a hollow refractory mandrel so that a tube of molten glass is forced vertically through an air blast venturi.  At the top of the mandrel was a series of air jets which cool the produced tube such that it solidified sufficiently to be grabbed and drawn upwards by pairs of friction wheels which lifted the tube two floors to a work station where it was cut to length.

Each length was gauged for external diameter and weighed to check both internal and outside diameter.  Any variation from mean specification was controlled by adjusting the speed at which the tubing was drawn.  The tubing required for CRT necks was cut to the required length and then fed into a glass lathe where it was heated with gas jets to soften the glass which was then formed into a conical bell which corresponded to the end of the CRT bulb.

The shaped neck was then transferred to another machine and held in a jig which held it approximately 40mm from the bulb aperture.  The jig moved around a carousel where gas jets were applied radially whilst turning the jig until the glass on both parts softened at which point the jig moved downwards until the plastic glass touched.  Continued heat and downward pressure ensured a perfect join.   The completed bulb continued to move around the machine with it's temperature being reduced at successive stations.  At one point of the rotation, an operator fused a hole in the side of the bulb into which an EHT lead-in connection was fused.   The EHT connection was a number of lengths of wire sealed into a glass bead ready for fusing into the bulb.  

Bulbs were then removed to an annealing furnace where they were slowly cooled to relax heat induced stresses, the most critical of these being at the bulb and tube joint area.  To ensure a no stress product with minimal risk of implosion, the join area was scrutinised under polarised light to show up any inherant weakness which had not been normalised by the annealing process.   The completed bulbs were at this time in the early 1950s transported by road to the Mitcham factory where the final processes to turn them into finished CRT were undertaken. 

We shall leave this story today with a nice photograph of the individual glass components of a Mullard Rectangular Tube: - 

GLASS ENGINEERING FOR CATHODE RAY TUBE MANUFACTURE (i)

In the very early days of television, the bulbs for cathode ray tubes (CRT) were blown by hand, however, due to volume requirements, most CRT bulbs were moulded, being made in two parts with the flattened end termed the face-plate and the pear shaped body termed the cone.  As the separate parts were delivered to the Mullard factory, at this stage in the early 1950s that means the Blackburn works, the first stage after inspection for blemishes was to join the parts.  Any components marred by blemishing were returned to the glass moulders for re-melting - waste not want not!

Joining was carried out using a multi stage joining machine with the face-plate and cone being held on a loading jig whilst touching each other, the fixture then commences to revolve and was moved to successive stations where gas blowpipe flames of increasing intensity played on all areas of the join until the individual parts were welded together, successive stations then reduced the glass temperature gradually with the bulbs finally being placed into an annealing furnace where they were left to cool to ambient temperature slowly hence  relieving any heat induced stresses.

So,  that's the cone and faceplate sorted, next time we'll look at the manufacture and attachment of the CRT necks.

 

AN INTRODUCTION TO CATHODE RAY TUBE (CRT) MANUFACTURE

Well, a CRT is a thermionic electron tube so I thought we would follow our popular blog series on how valves were made with a similar one detailing the manufacturing process for CRT employed by Mullard.

Let's start with the basics, we can list the CRT main component parts as the envelope, the electron gun and the screen.

The envelope, consists of a funnel shaped glass bulb which was either round or rectangular in section and closed at it's widest end with a flat glass faceplate and terminated at the other end by a narrow tubular neck.

The electron gun, produced a narrow beam of high velocity electrons that move toward the screen, the intensity of this beam being proportional to that part of the picture being transmitted.  It was made up of an indirectly heated cathode, a grid which modulated the beam with picture information and two high potential anodes which accelerated the electrons towards the screen.  Final focussing of the electron beam and it's deflection such that it sweeps the entire screen area was influenced by a focussing magnet and deflection coil combination located coaxially with the tube neck.

The screen, was coated with a fluorescent material which had the property of emitting light when bombarded by high velocity electrons.  The amount of light produced depended upon electron velocity (a function of EHT potential)  and the rate of electron flow ( a function of grid modulation and cathode emission).

More detail on the sequence of operations of production will be given in successive blog entries but for now, feast your eyes on the following photograph of 'modern' Mullard produced black and white cathode ray tubes - simply spiffing!

 

DRIVING LEXY AT VAST SPEED AND STILL POWER ON TAP!

Well, yesterday, my pal Greg, a classic car enthusiast and Bristol restorer let me drive his tricked up Bristol 603 at vast speeds.  As he exhorted me to go faster, I used the excuse of hellish fuel consumption by the 6.3l V8 rather than my own fear to ease off the loud pedal.

Here we see Greg perched on his shooting stick with Lexy, his sexy black beauty of a 1970s Bristol 603, once the property of Chris Serle - remember him from Windmill, That's Life and Points of View.   Lexy is available for immediate purchase at £39,500.

NEW HI TECH CLOTHES FOR MULLARD GIRLS!

In October 1952, Mullard made the headlines in that mainstream publication British Textiles!

"Spotless white nylon coveralls and coloured nylon headscarves are worn by all operatives in the assembly room of Mullard's new valve factory.  The well-founded reason is that the highest posiible standards of cleanliness must be maintained in an operation so delicate that the presence of lint or dust in the atmosphere could cause deterioration of the valves and nylon being non fibrous creates neither lint nor dust.  The girls are given a choice of four colours of headscarf: pink, light blue, green or lemon and it is interesting to note that the pink and the blue far exceed the other colours in popularity."

An interesting report, but I wonder what colour scarf the chaps wore.............

 

 

MULLARD LONG LIFE TINTED TELEVISION PICTURE TUBES

 

Today's evocative photo shows Mulard Long Life picture tubes undergoing life tests at the Mitcham plant sometime in mid 1952.    

On the test rig, applied voltages were regulated and the beam current was fixed.  The test card used closely simulated a screen raster.  Here we see Trevor Wibbley about to take voltage characteristc measurements, light output measurements and assess subjective picture quality.

What is special about the tubes pictured is that they were the first of those produced by Mullard with tinted glass faces.   The tinting was introduced as an attempt to boost contrast when viewing in daylight conditions.due to the tinting agent cutting down reflected light hence making the black  picture content appear much darker even though the tint did cut down the bright emitted light!

THE PYE W15FM/C WESTMINSTER, A FRANCIS-BARNETT FALCON AND THE LADYBIRD BOOK!

Ladybird books really bring back the golden days of childhood - learning to read, discovering the magic of books, and growing up.  It is more than sixty years since the first familiar pocket sized full colour Ladybird saw the light of day in 1940, during the Second World War with an animal series called Bunnikins and all for half a crown.

Ladybird books stayed at half a crown (2 shillings and sixpence = 12 pence today) for thirty years, because the 56 page standardised format (made from just one sheet size 40 inches by 30 inches) meant that quality books could be produced at a low price.

Those books of the 60s were so popular they were even affectionately jeered at. Michael Crawford in 'Some Mothers Do Have 'Em' had a book called 'Learn to Fly with Ladybird'.  And one noted politician asked in Parliament, 'Has the Right Honourable Member read the Ladybird Book on Politics? – I know that Ed Milliband reads his every evening and he has got to the stage where his lips no longer move as he reads!

In 1970-71 Wills & Hepworth, the manufacturer's of Ladybird books since 1915, moved to a new site in Loughborough, and the company name finally became Ladybird Books in 1971. Just one year later, the company was taken over by the Pearson Group in 1972, who at that time also owned Longmans, the Financial Times and Westminster Press, as well as diverse interests such as Madame Tussaud's, Royal Doulton (now you can see another Bunnikins link!) and a cross-channel ferry company.

The Learnabout books of the 60s were designed to help children to develop new interests whilst focussing on the factual side and this novel approach brought some unusual results.  Notably, the Ladybird book,  How it Works: The Motor Car (published in 1965) was used by Thames Valley police driving school as a general guide and today we have some quaint entries from a companion book  Your Career in the Police Force: - 

In the pages above, we see PC Blenkinsop calling for back up from his Francis Barnett Falcon F150 mounted Pye W15FM/C Westminster radio telephone whilst clearly anunciating his concerns to central despatch - stirring stuff.  We hope you are as impressed with the colour plate and incisive informative text as we are and for your further enjoyment, we show below a further two pages from this very interesting book. Ello, ello, ello, what's all this then...........: -