Hammond delay thingie (was: mysterious delay lines)

[Mike]

Hcabnivek at aol.com wrote:
> 
> Speaking of delay like devices  (though I'm not sure this real is one) can
> someone explain how the small motor driven drum inside a Hammond organ that
> has all the wires connected to it works to generate tremolo/varabrato.  I'm
> not talking about a Leslie here, this thing has a wire from each of the draw
> bars connected to it I guess a single output wire, and some rotating part
> inside that's turned by a belt running off the same motor that turns the tone
> wheels.
> Anyone?
> Kevin
Kevin,The Hammond device you are referring to is called a vibrato
scanner. It works something like the distributor in your automobile
engine. There are multiple fixed capacitor poles arranged in a circle
that are connected to different points on an inductor/capacitor delay
line that the organ signal is run through. There is a scanning pole that
rotates inside this assembly that capacitively couples the various
delayed signals to the scanner output. Since the delays are different as
the scanner rotates, the scanner output signal consists of a variable
time delayed version of the organ tone that shifts its pitch alternately
up and down thus giving a true vibrato sound.

Mike Granger