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Blog posts of '2012' 'April'

THE MULLARD ONE ARM BANDIT FROM DECEMBER 1950

Many users found the depression of the RHS handle to operate the Mullard High Speed Valve Tester  quite wearing -  and this at a time before  repetetive strain injuries were invented - stiff upper lip, grin and bear it!    The boffins at Salfords listened and voila, the tester was modified to have a one arm bandit style operating arm, not only that, if you pulled it and your valve tested for good emission, three cherries in a line appeared on the CRT.......................................  sorry couldn't resist that one.

Mullard advertised the change as ergonomics with  an added security measure, to stop customers from interfering with the valve tester, the knob and arm could be unscrewed to prevent meddlesome usage by  shifty spiv types and young schoolboys with caps, short trousers and sticky fingers. 

 

 

 

OOOH! GIRLS LIKE BIG UNS A LOT!

Well, whatever did you think, shame on you.........

You know, it is said that there is nothing new in show business or advertising and here we have three photos just to prove this point.

Here we see Petula Clark in October 1950 at the Castle Bromwich Radio Show somewhat agog at the size of this 5 foot Mullard valve model.

 

And this 'ad opportunity' was again exploited  with a young lady from  Chorley Wood College for Girls with Little or No Sight examining the same giant valve model at the London Science Museum in November 1950.

But this wasn't a novel approach at all, because in 1927, Telefunken's Frau Traudl Schmink did it first - and her valve was 2 metres in height, what a whopper!

 

 

 

THE MULLARD MASTER TEST BOARD & THE PHILIPS SERVICE TUBE TESTER
The Mullard Master Test Board (MMTB), introduced in 1935 is in actuality a re-badged Philips Cartomatic GM7629, often referenced as the Cartomatic Mk1.   In every other European country it was sold as the Philips Cartomatic but for some reason, Mullard badge engineered it as their own product.    Physical examination  of the Philips Cartomatic Mk1 and the Mullard Master Test Board side by side reveals identical construction leading us to conclude that irrespective of badging, they were all made by Philips and either supplied fully built or as 'knocked down' kits for British construction and then post manufacture rebadged as Mullard instruments.      Curiously, most Cartomatics appear to have a replacement meter which is of smaller diameter than the original,  the tell-tale being the diameter adaptor securing the meter to the front plate.   Obviously these gave some trouble in use which may have had a bearing on the design of the MHSVT which has a CRT for test indication rather than a relatively fragile moving coil meter. 
 
Here is an image of  the MMTB, courtesy of George Bichard - see the card slot and operating handle (20) on the right - does it look familiar?
  
 
 
 
 
The MMTB could also function as a multimeter as well.  In actuality, the MMTB was a Philips Service Tube Tester  (PSTT) with reduced valve testing capability but with multimeter functionality added in.      Also introduced in 1935, the PSTT was a professional grade machine used extensively within Philips' own laboratories and service centres.     Below, you can see a photo, courtesy of Jean -Yves Loizeau which shows such an instrument in use during the 1930s at a Philips service centre:-
 
 
And here you see a PSTT in it's full glory, working away, mercury rectifiers glowing in the rear and four beehive neons burning away on top - I cannot stress how rare a sight this is for to my knowledge there are currently only two PSTT known to survive, one in Philips' own Eindhoven museum and the one pictured here preserved in captivity in France under the care of Jean-Yves Loizeau.
 
 
   
Both the MMTB and the PSTT, like the MHSVT use plug in cards to input valve test parameters, however, whilst all three are similar, none of the three types of card are compatible with each other.   
 
 
 
THE EVOLUTION OF THE MULLARD HIGH SPEED VALVE TESTER
I have been corresponding with my new pal George Bichard, some of you may know George through his work to build a database  of all cards and issues of cards produced for the Mullard High Speed Valve Tester (MHSVT) , the Mullard Master Test Board (MMTB) and the Philips Service Tube Tester (PSTT)  – if you can help, fill gaps then George would love to hear from you – see what he needs and shout up if you are able to help, so please, look him up at  http://home.btconnect.com/gmb/mullard.htm
 
George and myself have been discussing the origins of the MHSVT between ourselves, in particular whether or not the MHSVT owes it’s lineage to the MMTB or the PSTT.   In the course of this discussion, we jointly realised that not many people have experience of the MMTB and even less people will know about the PSTT so I think I need to describe both of these instruments further in my next blog entry. 
MORE FACTS ABOUT THE MULLARD HIGH SPEED VALVE TESTER

Here we have a few more words on the MH-SVT from Mullard from 1951 along with a few of my own added in blue text:-

This valve testing apparatus is capable of carrying out tests as similar as possible to those standard production tests to which all Mullard valves are subject. The tests are not of course as exhaustive as those carried out during manufacture but they do ensure that the valve under test is satisfactory in all respects insofar as it is within the approved tolerances of operation.

Use of Punched Cards:  arrangement of the test circuit and selection of test parameters is performed using a  perforated card corrresponding to the valve under test.

This card is inserted into a gate switch contained within the valve tester.  Three such cards are supplied with each instrument for use when setting up and adjusting the tests.  Numbered and punched cards for the actual tests are available together with a printed list giving the valve types and the reference numbers of the corresponding cards.

Here's what the complex and slightly unreliable gate switch internals look like.

Three Test Limits:  in place of a moving coil meter, a cathode ray tube (CRT)  and vertical coloured scale are employed to indicate the results of various tests.  If the valve is within specified limits, the spot on the screen of the CRT is defelected to the green part of the scale.  If, on the other hand, the valve fails to meet the test requirement, the spot is deflected to the red part of the scale.  a reading in the intermediate part of the scale indicates that the test valve will soon need replacement.

But the real pity was that the  CRT based 'snog-marry-avoidometer'   style of indication allowed no quantitative estimation of valve performance to be made - the MH-SVT  was useless for valve matching.  


Construction:  the test apparatus is mounted in a metal case with a sloping front.  All internal components are readily accessible for servicing by removing one or more sections of the case. 

In the later 50s Mullard described the hammertone finish of the MH-SVT as being a 'densito finish' - can't think why though - perhaps it pre dated Hammerite!   The gate switch contacts were an inspired idea, however, their complexity made them liable to corrosion, arcing and consequent unreliability.

At the top right hand side of the front panel is situated the switch which selects the tests in sequence and below it is a rotary switch by means of which fine adjustment of the operating voltage can be made in accordance with the prevailing voltage of the supply mains.

To the left of the CRT are four buttons by means of which individual electrodes may be tested for short circuits, insulation and open circuits.

The front panel carries a removeable plate behind which are situated the adjustments for zero setting, reject limit setting, brilliance and focus and for lateral shifts of the spot in case phosphor burn becomes a problem, a fresh part of the screen may be used.

It is said that some dubious dealerships encouraged customer valve testing, often at the cost of 6d to 1/- on a MH-SVT whose reject limit settings has been adjusted very high so that a good valve would appear marginal.   A West Yorkshire ex TV Engineer pal told me that his boss bragged that  he achieved a 50% on test replacement valve sale rate by using this deplorable tactic. 

Mains Adjustment:   the instrument has been designed to operate on 50 c/s AC from 180 to 260 volts. Adjustment of the various voltages is by means of 20V tappings on the mains transformer located on the control panel in conjunction with an eleven position rotary switch operating in 2V steps situated on the indicator panel and marked MAINS ADJUST.

Initial & Periodical Check Routine:  to ensure correct function, special check cards must be used to check mains voltage against an internal standard.  Meter sensitivity and HT stabiliser may also be checked.

1950 & THE MULLARD HIGH SPEED VALVE TESTER - A NEW INSTRUMENT OF REVOLUTIONARY DESIGN

In January of 1948, a group of engineers at Mullard Research Laboratories, Salfords were given the brief to design and bring to production within two years (24 months), 'a valve testing apparatus suitable for use by dealers and service engineers'.  The aim was to showcase this exciting new post war development at the British Industries Fair Radio Show in late 1950 at the Castle Bromwich, Birmingham halls.   The target was met and sure enough, on Mullard's stand at Site 64, the 'valve testing apparatus' was proudly presented to the waiting market.

The design brief and the problems in meeting this requirement specification was interesting,  the new tester had to be 'modern',  compact, accurate, give a fast stable result - automatically, be easy to use by non-skilled personnel and finally, most important, be fitted with safeguards to prevent damage to tester and valve under test in the event of incorrect operation.  All this added up to a tall order indeed.

The 'modernity' aspect was provided by housing the new tester in a hammertone silver finished case having a low aspect, 'crouching' on the bench.  Difficulties with sourcing suitable moving coil meters for test indication allayed to the 'no damage on misuse' design brief lead to the novel concept of using a cathode ray tube for test indication - a twin edged sword - for although there was no meter to burn out, there was no way to get a discrete quantitative estimation of measured test parameters, however, it was felt that service departments only required a go/no-go indication anyway.  

It is quite amusing now looking back that much was made of the new tester's bench footprint of 16 inches square and a height of only 12 inches.  Not a bad result, however, this new tester drew much from the Mullard Master Test Board of 1935 in that similarly, it depended upon the use of punched paxolin cards to be inserted into a gate switch to set the test parameters for a specific valve under test - with over 8000 valve types in service and a requirement for at least 250 cards to cover the most common, storage for the associated cards was both bulky and commensurately heavy!!

We will look at the Mullard High Speed Tester in more detail in a future blog but I should like to finish by explaining  - in Mullard's own words - a little about what this device could do:-

"A non technical person could learn to use the new tester safely and effectively after 10 minutes of instruction.   After inserting the correct card for the device under test and utilising a simple arrangement of switch and push buttons can, under working conditions test for faults with: inter electrode insulation, continuity of electrodes, degree of emission, grid current, and heater cathode insulation with the position of a moving spot on the cathode ray tube indicating whether or not the valve on test is or is not within it's proper operating limits."

 Interesting though, that many preferred this little number by a competitor, similarly priced but slightly lower such that the savings would allow a pretty nice austerity lunch for two, pass the salt old bean, my Brown Windsor soup is a little insipid.  Sir Stafford Cripps would certainly approve.

BACK ON THE MULLARD TRACK

It's about time we came back on track and continued our historical look at Mullard.  The last blog entry on this subject  dealt  with changes in the radio, television and valve market in the late 1950's and generally how the Mulard organisiation adapted to follow these changes.  I should now like to take a look at the pivotal products, personalities, problems and production facility developments from this period in a little more detail.   Let's choose our pivotal product from the 1950s,  well, it's got to be The Mullard High Speed Valve Tester, coming soon to this blog.........