[HBR] Regenerative communications receiver

[Walt Hutchens]

Radio said:

> They were used in "VT" ammunition.. typically, VT-frag and VT-non frag.
> Essentially an oscillator that when approaching a metallic object went off
> freq, and shazzam.. or at least that's how it was explained to me.

Yep. A VHF oscillator that also served as an oscillating detector
could sense nearby metal (Doppler effect from reflected wave caused
audio variation in the plate current) and would then trigger a
thyratron. Four subminiature tubes but these tubes were developed
specifically for this application -- thousands of G's acceleration and
a useful life of seconds! -- and weren't used for anything else.

Next to the atom bomb probably the most important American technical
advance of WW II.

There's a good Wiki article at:

https://en.wikipedia.org/wiki/Proximity_fuze

Subminiature receiving tubes are useful for the home constructor
mainly in battery operated gear. Once you get into indirectly heated
tubes the advantage of having two (or more) active devices in one
envelope gives the nod to miniature tubes for most applications.
Additionally, driven by the TV market miniature tube development went
beyond where subminatures quit so there are better tubes for many
jobs.

Subminiatures are easy enough to use for one or two tube designs where
the size payoff is small; once you get to more complex gear the wiring
technique and need for subminiature transformers, tuning caps, etc. is
a real challenge. But they were heavily used by the military in the
late 50's and 60's. Emergency sets for downed pilots, handy-talky
PRC-6, the backpack PRC 8-9-10 sets, etc.

Consider the size of the ~1950 SRR-11/12/13 sets: Just about as bulky
as any other communications receiver of the day, even though
subminiature tubes were used throughout.

They may be somewhat less fragile than miniatures, however I once
dumped a small box of subminiatures on a tile floor and about 1/3 of
them broke.

Walt
KJ4KV