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Blog posts of '2012' 'December'

DON'T BLAME THE BBC!

 

Here we see in happier times, a large poster proclaiming DON'T BLAME THE BBC!    Whatever for as Jimmy Saville was just a lad playing with his Dinky toy (ooo-eeer) at this time!!!!!!!!!!!!!

In actual fact it's a Mullard poster at the Northern Radio Show of 1952 telling visitors that they mustn't blame the BBC for poor radio performance as it may be a failing valve that has robbed their set of sparkle.   The dashing brilliantine-esque gent was Ronald Waldman who at that time was the BBC Head of TV & Light Entertainment.  

Interestingly enough, do you see the cartoon characters on the poster? ..... do they look familiar? ...... well, if you are a fan of St Trinian's (I am sure our Jimmy was!!!!) then indeed they  should do as they were penned by none other than Ronald Searle, the famous satirical cartoonist and creator of the St Trinian's schoolgirls.   Owzabout that then!

 

BOOST RECEPTION, RE-VALVE WITH MULLARD MAGIC

 

What a top seasonal thought, dating from 1953 we have a photo of a Mullard inspired shop window display - simply super!

VALVE TYPES & MANUFACTURING TECHNIQUES (xxii) - B7G & B9A VALVE ASSEMBLY - TEST 2, WAREHOUSE TESTS

Ho, ho, ho, it's Christmas day and time for the next blog entry.  The final tests  described in my last blog entry were known as Test 1 and these allowed passed stock to be released from quarantine into Factory Stock.  Before valves were issued from Factory Stock to the warehouse for despatch to customers, they underwent a second series of similar tests to Test 1 by a second independant quaity control group.  These were known as...... wait for it...... Test 2.

VALVE TYPES & MANUFACTURING TECHNIQUES (xxi) - B7G & B9A VALVE ASSEMBLY - TEST 1, FINAL TESTS

After passing the knock test, valves were passed to the main test bench and plugged into a test board where a specially designed  eight position switch  applied successively, appropriate voltages such that values were obtained for the following parameters: -

Heater current

Cathode current

Control grid current

Screen current

Anode current

Total emission

Mutual conductance ( at 4 - 7 points on the characteristic curve dependant on valve type)

Inter electrode insulation for all electrode combinations

Only those valves whose performance fell within specified limits were then passed into "Factory Stock."

 In the photograph below we see Enid Barribal testing valves using one of the Mullard Blackburn 'Test 1' main test boards: -

 

Mullard Blackburn also had a semi-automated final test board where valves were plugged into sockets mounted on a revolving platter.  As each valve passed from station to station, the various tests were automatically applied but the indicating instruments on the test board were replaced by sensitive relays which would energise if a faulty valve was detected hence activating an automatic claw to pull and dump the faulty valve in a reject tray.

VALVE TYPES & MANUFACTURING TECHNIQUES (xx) - B7G & B9A VALVE ASSEMBLY - THE "KNOCK TEST"

After ageing, the valves were ready for a series of intensive tests during which any valve which failed specification was rejected.  The first of these tests and the first hurdle at which the valve could be failed was known as the "Knock Test."

To conduct a Knock Test, the valve was plugged into a test board and the appropriate voltages were applied to all electrodes. The valve was then sharply tapped several times with a rubber hammer and any hidden faults such as intermittent short circuits or loose connections were indicated by readings on a series of meters or the lighting of neon lamp indicators.  The object of this test was to weed out any valves which were hopelessly defective and which had the potential to damage the very delicate instruments utilised for the final tests which we will be discussing in my next blog entry.

 

VALVE TYPES & MANUFACTURING TECHNIQUES (xix) - B7G & B9A VALVE ASSEMBLY - AGEING

And so the story continues.......... a couple of blog entries ago, we left the production process at the sealing stage at which point we had a sealed and functioning valve, however, further processing was required before it was suitable for use for it was required to undergo a process called ageing.

Ageing consisted of operating the valve under load under carefully controlled conditions.  Large numbers of valves were plugged into a socket rack like the one in the photo below: -

Once the rack was fully loaded, the valve heaters were activated at a 20% higher than nominal rating, so for a 6.3V valve, a Vf of 7.5V would be applied.  The control grid would have a positive potential applied and both these effects served to 'boil off' electrons from the emissive cathode which in turn caused a small proportion of the barium and strontium oxides to be reduced to metallic barium and strontium.  This was a desirable characteristic as the presence of these transition metals served to increase the cathode's emissive properties.   After a prescribed time, the grid potential was reduced to zero, cutting off electron flow and the ageing was completed by running the valve at a low cathode current and with the Vf reduced to it's nominal rating.

Across the water, at Philips Herleen, they also aged produced valves but utilised a slightly more modern and certainly more ergonomic valve ageing rack as you can see from the following photo Bart Fokkink is tending an active rack: - 

 

A COVER FOR YOUR MULLARD HIGH SPEED VALVE TESTER

In March 1952, if you wanted to spruce up your service department, you could buy a smart, dustproof, tailor-made cover in strong silverised leathercloth for your MHSVT.   It had red piping accents and was only 13/-.

Here we see Hortense Balchin who stated that 'My Wilbert always said that a workman must care for his tools and they will go on to care for him." and she went on to demonstrate how clean this cover kept her Wilbert's instrument : -

MULLARD VALVES FOR HEARING AIDS - PARDON?

Now then, everyone tends to think of Hivac when they think of miniature valves for hearing aids but Mullard made them too.   Hearing aid valves were specialised in that they needed a small envelope size, must operate at low filament current and be non microphonic.

Due to the National Health hearing aid being introduced in 1948, Mullard developed a series of 10mm subminiature valves to power it ......we have two of these smashing hearing aids available for sale elsewhere on the site - anyhow, I digress.........

These 10mm specials  were swiftly superceded by the DF66, DL66 and DL68 which show a 15mA as against the 35mA used by the previous types.  And this was done by the use of 8 micron (3/10000 inch) filament wire - now that is small as you can see in the photo below, on the left, we have a spider's web with sticky blobs on it to trap insects, on the right, we have the hearing aid tungsten wire, pretty neat huh?

The next picture just shows how small the 1950s hearing aid valves from Mullard actually were, their size approximated to   1/40th the size of a typical radio valve: - 

My last picture shows, progressing from left to right, how hearing aid valves from Mullard shrunk from the 1936 original to the 1947 10mm and finally the 1952 D series: - 

This development work on hearing aid valves served Mullard well as variants of these were used in the Ferranti radars of second generation RAF fighter jets such as the Lightning and the Buccaneer.

 

MERRY CHRISTMAS 2012 FROM MULLARD MAGIC

Don't forget to buy your loved ones a present from Mullard Magic's extensive stock of unique gifts.  After all, who would want a pair of luminous reindeer socks from Marks & Sparks when you could have a bolometer,  valve or klystron from MM!!

Joking aside, to all our customers, thank you for making our first year a success and seasonal greetings to you all, we hope you enjoy this copy of a Mullard Christmas card sent to management team members in 1952: -

VALVE TYPES & MANUFACTURING TECHNIQUES (xviii) - B7G & B9A VALVE ASSEMBLY - PUMPING

In this process, where sealed valves were passed from the last station of the sealing machine, a mechanical tri-claw hand fitted with an asbestos glove (imagine the 'elf n safety implications today!!!) transfered the valve to the first vacant position on the pumping machine.

The pumping machine comprised of another rotating table which had a sequence of rubber bungs around the periphery.  Each bung was connected to a vaccuum manifold supplying a high torr vaccuum.  As the valve abutted a bung, the process of pumping commenced.  As the valve rotated around the table, the valve passed through a heated convection tunnel where the high temperature assisted in driving off air and other gaseous contaminants.  

The valves then passed through loops of copper tube carrying radio - frequency (RF) current.  The RF served three purposes by raising internal temperatures, firstly,  to induce RF eddy currents in the metallic parts of the sealed valve which drove off any interstitially occluded gas; secondly, to sublime the getter material such that an active flashing coated the internal envelope; and finally to convert the filament barium and strontium carbonate coating to form the emissive oxide - all this going on whilst the pumping still continued!

Finally, when a satisfactory vaccuum was pulled, the pumping sprue was cinched and the valve finally sealed off using a fine glass flame played at a point close to where the pumping sprue meets the envelope top, accordingly,  the glass fuses with the characteristic pip at the envelope top being left.   A second tri-claw hand then removed the pumped valve from the pumping table.

In the photo below, we see Roger Beardshall at one of the Blackburn pumping machines: -