Blog posts of '2013' 'August'



Today's blog entry shows a 1930s cartoon which I couldn't resist - it reminds me of the time I tried to resolder the wire on a roller-coaster - boing, disaster.   The cartoon is by Mabel Lucie-Atwell, a famous British illustrator who also went on to design and decorate for Shelley pottery and even invented a series of small green elvin characters called the Boo-Boos.


Today's blog entry shows a Whyteleafe Valve Assembly girl examining grids for lint and spacing errors some time in 1952.  She is using a projection epidiascope to view and manipulate the grid windings as necessary.



Hah,  I bet that title got your interest piqued and I'll bet it's not what you thought either.   The Touch of a Woman's Hand was the title of a BBC Eurpoean Service radio broadcast from 30th July 1953 by C. L. Bolz the then Science Correspondant of the BBC made describing a visit to Mullard Whyteleafe.

I have transcribed excerpts from the script drawn from Mullard archives with which to regale you with.  I do hope you will read this using your best Mr Cholmondley-Warner accent and inwardly cringe at the bloopers and non PC faux-pas as our modern day conventions would call them - for your delectation: -

After telling his listeners what was inside a valve, Mr Bolz 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 fit into a thimble, you can imagine the degree of delicacy required, for the metal filament used in such a valve is about one tenth 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 did not exist - and I must say that this amusing description was no exaggeration for I saw girls doing it!"

The problem hand jobs can cause - "Naturally, the more an industry depends upon the skills of thousands of hand workers, the greater is the possibility of quality variation and this used to be the case in the valve industry; the percentage of rejections was enormous but has now been reduced by attention to process detail and better design of electrodes for ease of assembly.   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 know firm (Mullard) to introduce new methods into the manufacture of sub miniature valves that have aroused great interest in visitors from many countries.  I saw the methods in use.  The wastage is reduced to far less than 2%, even 1% with a few star performers.   

New equipment too - "The first part of the technique so applied was to design gadgets that reduce the error in assembly, jigs as the engineer calls them, so made that at final assembly, the electrodes can be put together one way only and in no other way.  And here I must emphasize that the aim is to produce valves in large quantities."

Young girls are best at it - "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 or eye strain."

Novel, new training methods - "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 the minimum of bell rings.  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 compicated device is to train independant finger control.  Every mistake lights up a red light."

Give a girl a tool and she'll finish the job - "The welding of the tiny electrode to the connecting wires is done by electricity and the welding is taken to the job, not as in the past where the job was taken to a rather clumsy welding machine.  It's done by haviing a plugged electricity supply at every worker's station and a pair of insulated tweezers for the actual welding.  All components are covered with plastic sheeting when not actually being handled.  A powerful magnifying lens is at each station so that each tiny assembly may be minutely 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 a virtue - "Cleanliness is of supreme importance as a speck of dust on a grid would make the valve useless so the girls wear nylon overalls and hair shields as nylon does not produce fluff - and the factory, cleaner and lighter than many a laboratory I have seen - is cleaned by a vacuum cleaner every day."

In summary - "Naturally, I have left out much of the technique such as the ingenious devices used in the evacuation of the glass bulb and the like.  But, I have told you enough to show you that here at the new Mullard factory in the Surrey countryside near London, a system has evolved that may revolutionise manufacture of 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 that they are a happy crowd and I know there is no shortage of applicants for jobs."


Today's Mullard archive photograph shows a Mullard Whyteleafe Valve Assembly Department operator removing an electrode cage from one of the dustproof boxes in which valve components were stored when not undergoing manufacturing operations.  As you can see, the operator's right hand holds a pair of welding tweezers with which she is about to weld a getter bar onto a selected electrode cage. 

The BBC European Service Science Correspondent in 1953 was CL Boltz and he had much to say about the valve assembly operations but that is a subject for another day and another blog entry.


Valves as we know, have many different functions and for each application there are certain parameters which ensure the best use in these applications, for example: -

For an audio amplifier - knowledge of the maximal power output and distortion of an output valve for various levels of signal input under variable anode load resistance and grid load resistance is important.

For a radio receiver - knowledge of the cross-modulation factor allows effective choice of frequency changer valves and IF amplifier valves so that effective AGC circuits may be designed.

In order to measure these parameters and others such as equivalent noise resistance, hum level, conversion conductance, power output and harmonic distortion, the Mullard Valve Measurement & Applications Laboratory designed and built in house a range of test rigs which would test these parameters  The design of each of these instruments was particularly elegant in that circuit components and input voltages were infinately variable and easily switchable and that obtained test results could be directly read from meters and indicators which were calibrated in the units required without having to  resort to complex calculations.

The results of these basic dynamic measurements were used at key stages in the history of a valve type.  During development and pre-production trials, samples were tested to ensure the performance of a new valve met the required specification.   In production, similar measurements provided information for publication in valve data manuals and application reports.  When the valve was an established production line, checks were made on sequential valve batches to ensure that consistency of performance was being maintained.

In today's Mullard archive picture shown below, you can see a Mullard Valve Applications Laboratory physicist in the foreground measuring Equivalent Noise Resistance, on his right, a colleague is working the test rig for measuring Power Output and Distortion: -



Wahey! Those awfully nice Mullard Magic people are now on Twitter!

— Steve (@MULLARDMAGIC) August 16, 2013
Now we shall be tweeting each time we put new stock up and giving you a handy link within the tweet so you can quickly see what new treasures and delights we have on offer.

As well as the production testing we discussed in a recent blog entry, Mullard employed Quality Control (QC) testing where a sample of ten valves were taken at regular intervals  and subjected to a range of tests.  These tests differed from the production tests which were go/no-go type in that the QC tests were quantitative and the results were recorded using a series of Shewart Charts to individually log test characteristics both within a single batch and also inter batch.

The Shewart Chart is a time related plot which allowed trends in measurement to be monitored.  The chart would have on it's y (vertical) axis two sets of bars - the first, the warning limit, the second, the specification limit.    Corrective action would be taken if measurements approached the warning limit before the specification limit was exceeded and the valve product had to be scrapped.

Although some of the QC tests followed the 'Test 1' protocol, additional tests were also carried out.  For indirectly heated valves, there was a test on heating time and for battery valves, a series of tests to indicate performance when HT & LT batteries run down.  Inter-electrode capacitances were measured for all HF valves along with tests for input damping and equivalent noise resistance.  For voltage amplifying valves (ie - audio ) measurement of gain was undertaken.  For output valves, total harmonic distortion for a given output was measured and microphony tests were made when considered appropriate. Frequency changers were given a custom sequence of tests to measure conversion conductance and oscillator performance.

As you can imagine, this barrage of tests required custom built equipment which was designed and constructed in house and below, you can see a photo of a Mullard Blackburn microphony test station giving an EL37 a good seeing to: -



Another QC test was the Life Test where test valves were over - run for a 600 hour test and subjected to the 'Test 1' protocol at intervals throughout the test period.  

The results of all of these various QC tests were produced at a weekly 'round table' where representatives from the Mullard departments of Production, Laboratories, Development and Technical Service could discuss the findings and as necessary recommend and implement minor modificatons in construction and manufacturing methodology to improve performance and hence correct undesirable trends.


Mullard Magic went on tour last week and on one day rolled up at the Morgan Cars factory for a guided tour.  Now, I once ripped my trousers getting into a Morgan when I was younger (and thinner!!) so I have never been a keen fan of them but I am very impressed with the newer breed of Morgan Aeromax with it's Talbot-Lago-esque rear end and at £107k every household should own one!   With the passing of Bristol Cars into foreign ownership last year, Morgan remains the only wholly British owned private car company left.   

Interestingly Dixon, our guide at Morgan bought his Morgan in 1955 and had turned down an offer of £120k from a keen prospective purchaser last year, talk about a gold plated investment, now that really is an impressive return!

Feast your eyes on the following video so you can see what the tour was like: - 





Remember these? ...."The Mullard Expandabox Units have been designed after careful study of dealers' stocking problems to store valves neatly and methodically."         

 Mullard went on to say...."Each unit is specially sectioned to allow valves to be easily withdrawn and to prevent small valves being pushed through to the back. The uniform height and depth of the Units enable those containing valves of varying size to be stacked side by side."

A further revalation was..."The space and shelving facilities at your disposal present no difficulties in the case of Expandabox valve stocking as odd spaces can be filled by stacking units horizontally and the robust construction of the Units enables large quantities of valves to be stored without any special shelving with a metal clip holding each Unit perfectly rigid."

A quite prescient pont made before the days of kan-bans, home (or shop) computers was.... "The Expandabox Units provide an automatic stock control for whenever a valve is withdrawn an obvious space is left. The job of re-ordering valves is further simplified by indicating the appropriate valve type numbers inside each honeycomb section and bright yellow labels (just like the ones Mullard Magic uses for valve data records!!!) have been designed for this purpose."

And all this was available in a unit holding three, four, five or twelve valves - each holding the requisite standard sized Mullard cartons for just sixpence and were a jolly good product for the tidy workshop conscious valve hoarder:-


These were a well established workshop aid by the late 1950s and during 1958, the Mullard technical services group received a letter from a worried chap in Halifax enquiring about the purchase of Expandaboxes to construct a nuclear fallout shelter. Questions were raised about how best to secure the Expandabox stacks to the exterior of a sturdy oak dining table - was passe-partout tape and chicken wire or Seccotine the most suitable fixative?  Unfortunately I don't have Mullard's reply to hand. 


How times change, these days, event stands are put up by gum chewing muscle bound chaps wearing Dickies work pants and steel toe capped boots, however, in 1953 as you see here, the Mullard stand at that years radio show was erected in all it's glitzy splendour by chaps in suits and ties - stirring stuff!



In 1953, Mullard had two locations at this venue.  First there was Stand 91 which boasted information centres for listeners and viewers as well as a comfortable lounge where commercial and technical problems affecting valves and cathode ray tubes could have been discussed with eager Mullard representatives.  In addition there was also Demonstration room D7 which was devoted to trade demonstrations of the MHSVT and the Expandabox system - more on this development and a hilarious story as well in a future blog!