THE GREAT MULLARD MAGIC BLOG — tungsten wire

In the preceding two blog entries, I have discussed how tungsten wire was produced by Mullard's - incidentally, exactly the same process was used to make molybdenum wire too.   Both of these wire types were used to manufacture the grids we see in multi electrode cages.   As you can no doubt imagine, the performance of a valve is dependant upon extreme accuracy in the winding and positioning of these grids so let's have a look at what's involved in doing so. Let's consider the Mullard EF86, a B9A pentode used for many applications from TV IF strips to...

OK,  for today's blog entry I promise that I am not going to act like a  Chemist wonk (even though I am one!)  but rather instead, a thermionic wonk ( because I am one as well)!!!!!.     Last time, we took a look at Tungsten, an essential commodity used in wire for just about every valve ever made.  We left the story at the metallic powdered tungsten stage and picking up the tale again, here we have a nice ex-Mullard photo of a batch of the fine dark grey powdered tungsten leaving one of Mullard Blackburn's reduction furnaces: -...

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...

Let's look at the CATHODE today.  Of the two types of CATHODE construction we commonly see, I am today going to describe just one - the directly heated cathode.      Directly heated cathodes are often seen in battery valves and power rectifiers, these tend to be filament wires or filament tapes coated with an emissive cathode material.  Just take a look at the shadowgram below where we have, from L to R:- a human hair, a coated directly heated filament for a DF66 valve,  an uncoated filament for a DF66 valve. The filament wire used for diretly heated cathodes...