Operators at a Mullard factory using welding tweezers to secure the electrode structures of miniature valves.
A visit to the Mullard factory at Whyteleafe, Surrey, by C L Boltz, Science Correspondent of the BBC European Service, resulted in a talk broadcast on 30th July, 1953. With kind permission of the European Service we now publish extracts from the broadcast script.6>
Mr Boltz began his talk by explaining its title.
I really ought to say the touch of womenbs hands, in the plural, because Ibm really concerned not with romance but technology. The delicacy of the feminine touch has been known and made use of in industry for a century or so, but the modern trend is to create complicated machines that do automatically what women used to do at the production bench - some products are even advertised as being untouched by hand.
Now, therebs one industry at any rate in which this does not apply. It is the manufacture of thermionic valves. These valves are everywhere to-day - not only in the radio receivers used by millions of people like yourself, but in the thousands of electronic devices from deaf-aids to electronic computers, each of which may have a thousand or more thermionic valves in it.
After telling his listeners what there is inside a valve, Mr Boltz explained that the component parts are assembled by hand.
This is very delicate work, even in the valves of ordinary size, and when they are deaf-aid valves, so small that three of them will go into a thimble, you can imagine the degree of delicacy required, for the metal filament used in such a valve is about a tenth of the diameter of a human hair - as one observer put it, watching the girls at work, he saw a girl picking up nothing and putting it into a space that didnbt exist - and I must say that this amusing description is hardly exaggerated. I saw girls doing it.
Naturally, the more an industry depends on the skill of thousands of hand workers, the greater is the possibility of a big variation in quality, a big departure from what is acceptable. And this used to be the case in the valve industry; the percentage of rejections, by industrial standards, was enormous. It has been considerably reduced by careful attention to details of the processes and by better designing of the assembly of electrodes. But it is still too high to be tolerated by any firm that cannot afford wastage, and certainly no firm in Britain at the present time can afford it.
New manufacturing techniques.
This has led one well-known firm to introduce new methods into the manufacture of sub- miniature valves, totally new methods that have aroused great interest in visitors from many countries. I saw the methods in use. The wastage is reduced so far to less than 2 per cent, even 1 per cent with a few star performers, and this order of wastage is very low even for any sort of manufacture.
The first part of the technique so applied is to design gadgets that reduce the error in assembly, jigs as the engineer calls them, so made that at the final assembly the electrodes can be put together in one way only and in no other. And here I must emphasize that the aim is to produce the valves in large quantities - mass production, not just a few special valves. The jig for the sub-miniature valve is the result of highly ingenious designing by engineers.
New training methods.
The next part of the technique is the preliminary training of the girls, a totally new departure. The girls are not accepted for training over the age of 25. Before acceptance they have a stringent eye test to make sure not only that the sight is perfect but also that there is no likelihood of fatigue and eyestrain.
The novel training methods make use of devices that train hand-and-eye co-ordination. One of them is simply a bent wire standing up from a wooden base. The task is to thread over this wire a metal disc, and thread it over quickly and accurately so that it does not touch the wire during the threading. When it does touch, a bell rings, and training is not satisfactory until a girl can thread a certain number of discs every minute with a minimum of touches. Another gadget trains the touch without sight to help. The task is to thread over three upright rods, a disc with three holes in it, the job being done behind a screen so that the girl must feel the correct action. Yet another, more complicated, device is to train independent finger control. Every mistake lights up a red light.
Mr Boltz told how each girl keeps a record of her progress, thus becoming her own inspector, and continued by describing a new welding technique.
The welding of the tiny electrode to the connecting wires is done by electricity - and herebs another novel point, the welding is taken to the job, not as in the past, the job is taken to a rather clumsy welding machine. Itbs done by having a plugged electricity supply at every workerbs position and a pair of insulated tweezers for the actual welding. All components are covered up by plastic sheeting when not actually being handled. A powerful magnifying lens is at each position so that the tiny assembly can be inspected by the girl herself. She has a position of her own complete with jig, lens, welding forceps, trays of components and assembly stand.
Cleanliness is supremely important - a tiny speck of dust on a grid would make the valve useless. So the girls wear nylon overalls and hair shields because nylon does not produce fluff, and the factory - cleaner and lighter than many a laboratory Ibve seen - is cleaned by vacuum cleaner every day.
Naturally, Ibve left out a lot of the technique, such as the ingenious devices used in the evacuation of the glass bulb and the like. But Ibve told you enough to show you that here at the new Mullard factory in the Surrey countryside near London, a system is being evolved that may revolutionise the manufacture of the thermionic valves needed nowadays all over the world, under the sea, on it, on land, and in the air. As for the girls - I judge as a mere man of course - they are a happy crowd, and I know there is no shortage of applicants, for jobs.