THE GREAT MULLARD MAGIC BLOG

How I tittered when I saw this 1926 advertisement for The Senior Dragon loudspeaker by Amplion.   You see, I refer to my Mother-In-Law, the Honourable Dowager Duchess June as the Senior Dragon. Like her, I'll just bet that this horn loudspeaker was LOUD!!!

Eh up peeps, it walks.... it talks.... it's all-ll-ll-most human AND it's got a Nixie tube watch, yes it's me Mr Mullard Magic with my genwine thermionic watch.   It comes to me courtesy of my good friend and even better customer Andy Smith, many of you here will know Andy as a Head-Fi big cheese and organiser of the 2012 Head- Fi meet near Cambridge. But before you do, check this watch out, titanium case, big enough to make an Olympic shot putter's wrist look puny and big enough for my 56 yo eyes to see....  All I do...

Last time, we only covered half the story about the CATHODE and today we'll look at the indirectly heated type.  These have a construction in which a pure metallic nickel tube is sprayed with an emissive coating admixture comprising of barium and strontium carbonate.    In the picture below, you can see the various stages taken to produce an indirectly heated cathode tube, and working from L to R these are: - cut; reamed; end swaged; pointing for mica location, flattened; lower end pointed; connecting strip welded; etched to allow emissive coating adhesion. Once the cathode tube is coated, a...

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...