Strange modulation schemes

Eric Barbour svetengr at
Wed Jun 25 20:23:25 CEST 1997

All this talk about random CV generators (sometimes called
animation CVs) makes me think of a somewhat demented scheme
I thought of recently for my tube synth circuits.

John Atwood has this General Radio pink-noise generator from
the 1950s. It uses a 6D4 thyratron surrounded by a big alnico
permanent magnet. Apparently the field biases the ionized
gas, producing substantial noise. It is sensitive to the
magnetic pole placement versus the thyratron internal structure.
A bizarre scheme, but it apparently works well.

So: why not glue a bunch of small rare-earth magnets to the rim
of a wheel and spin them past a tube? Use a motor with a speed
control. This would work with ANY kind of tube....12AX7 or pentode
amplifiers, beam modulators, even the thyratron VCOS in my synths.
The small magnets used in disk drives are cheap, readily available
as surplus, and VERY strong. Glue them to the wheel in any
desired pattern, and you'll have that pattern imposed on the 

BTW: has anyone here tried using tubes in their diy modular
synths? Want to share circuits, etc?

Eric Barbour
Svetlana Electron Devices
Portola Valley CA USA

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