[Milsurplus] subminiature tubes question

[J. Forster]

I am privileged to know the original developer of the submini tubes, Norm Krim
of Raytheon. He's still going strong in his 90s. According to him, the subminis
were originally developed for hearing aids in the late 30s and were then used in
the Proximity Fuses. There is a good book about such fuses, 'The Deadly Fuse',
which was made into a PBS 'Nova' show of the same title.

The design is very clever. When fired from the gun, the fuse is powered down.
Either centrifugal force causes electrolyte to flow into the battery or a
propeller on the nose of the fuse drives a dynamo. The RF part is a Tx and Rx
combined and produces a Doppler note. When this note is strong enough and in the
right frequency range, the shell explodes. One benefit of having the tubes
unpowered during the firing is improved resistance to shock.

I suspect the indirectly heated tubes were developed later in the war, when the
mini tubes were used in the increasingly complicated equipment that was
developed.

They were clever engineers in WW II.

-John

Bob Camp wrote:

> Hi
>
> In terms of number of tubes produced I think it's pretty clear that the
> winner is "almost all".  In addition to the stuff we normally think
> about using these little things also add to the list:
>
> Sonabouys
> Proximity Fuses, both in shells an bombs
> Hearing aids
>
> I suspect that the first categories each used more sub min tubes by
> them selves than all the military radios did. Given the cost drivers on
> that stuff I'm sure they went with filament tubes rather than the more
> expensive heater type. No need to spend that extra dime .....
>
> Anybody out there with a proximity fuse collection care to comment ?
>
>         Enjoy!
>
>                 Bob Camp
>                 KB8TQ
>
> On Jul 19, 2004, at 9:13 PM, aGEnuine Ham wrote:
>
> > Were all subminiature tubes filament type?  Almost all?  Almost none?
> >
> > Just thought I would throw that last one in to see if anyone was paying
> > attention.
> >
> > 73,
> > George
> > W5VPQ
> >
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