Strange modulation schemes & Chaos

Eric Barbour svetengr at
Fri Jun 27 00:47:02 CEST 1997

Dan Slater wrote:
These instruments produce various oscillations
and noises and which are controlled by how the instrument is
illuminated. The weak magnetic field causes the electrons emitted by the
photocathode to spiral apparently using a mechanism similar to that of a
microwave magnetron.

There were special digital decimal counter tubes made in the
1950s-60s by Burroughs which exploited this effect. The magnetic
field caused the electrons to describe a mathematical curve
called a TROCHOID. Thus, the tubes were called "Trochotrons".
The first version was the 6700, a big glass tube with 27 pins and
surrounded by a large cylindrical alnico magnet. Later versions
incorporated small magnets INSIDE the tube and were called "Beam-X"
counter tubes. Quite ingenious--supposedly able to count at up to
2 MHz. I have some....thinking of making a tube sequencer with one....
(they directly drive Nixie display tubes too!)

Eric Barbour
Svetlana Electron Devices
Portola Valley CA USA

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