THE GREAT MULLARD MAGIC BLOG

We've seen so far in my blog series on valve types and manufacturing techniques that fine wire is an important material used in the valve making process. To recap, tungsten wire is used as filament wire with molybdenum being used as grid and filament supports. Just to give you an idea of HOW essential this material was, in the Mullard Blackburn plant heyday of the early 1950s over 2500 MILES, yes, MILES of wire was used every WEEK in valve manufacture. So, where does the tungsten come from?, how is it formed into wire?, well paisan, read on and all...

A filament current drain of 1A was a real problem and the search was on to achieve good electron emission from a reduced filament current.  Early efforts were based on the use of alkaline earth metalled filaments where tungsten was doped with thorium, barium or strontium oxides before drawing into filament wire.  Development progressed  until a final configuration of tungsten wire, overcoated with a thorium oxide layer was settled upon.     This greatly reduced filament current consumption and had the side effect of a valve loosing it's bright but homely glow.   As a consequence, these new low current...

Back in the dim & distant past, in a land far away, shrounded in the mists of time there was a valve................... and what a valve, not like the ones we have today, oh no, it was very different indeed.     At the time, it was very similar to all its contemporaries - not that there were so many -  and like them,  it was a general purpose triode having a four volt pure tungsten filament which operated at a temperature similar to that of an incandescent light bulb.  The electrode cage was mounted an an inverted pedestal sealed...