Strange modulation schemes

Dave Halliday dave.halliday at
Thu Jun 26 06:02:38 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 
>     signal.


You could also use the "tuning eye" flourescent tubes and use a
photocell to pick off the values.

There is also a fun sort of feedback that can be done with a TV 
monitor and camera - focus the camera on the monitor.  YOu can get 
nice random pulsating patterns - tilt the camera a bit and also pass 
your hand between the two.

I once did a show that had film cans with CDS cells glued to the face 
of a B&W monitor - used nice thick cable coming out the back.  These 
went to various CV inputs and the camera focused on the room.
--- Via Silver Xpress V4.4 [Reg]

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