THE GREAT MULLARD MAGIC BLOG

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...

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...

Just been shopping and stood behind some idiot at the checkout and had to endure overhearing a banal conversation whilst the poor harried shop assistant was waiting for the little darling to pack and pay.    Mobile phones - what a curse - sometimes I wish I went around with a 800 - 1300MHz white noise generator!!!!! Imagine my surprise when I then came across this wonderful photo from 1979:- I do believe that this is Michael Rodd extolling the virtues of the latest elec-trickery invented by those clever people at Marconi Laboratories in Chelmsford. What we have here is a...

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 : -

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...