Strange modulation schemes & Chaos

Dave Halliday dave.halliday at
Fri Jun 27 04:56:20 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!)

I remeber seeing them on lab equipment in the 50's and 60's.

My dad is a physicist and I would visit the labs whenever I could. 
Scalars and Counters were bit things back then.

I remember that these tubes were really expensive - I wanted to build 
a counter for myself and they were the equivalent of a couple hundred 
bucks each ( in todays money )

Wound up doing a binary counter with multivibrators
--- Via Silver Xpress V4.4 [Reg]

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