Vacuum tube VCO with expo control.

media at media at
Wed Nov 24 20:18:16 CET 1999

At 11:08 PM +0100 11/22/99, Rene Schmitz wrote:
>This VCO is mainly meant as an example that solid state circuitry can be
>used in conjunction with vacuum tubes, to improve the overall flexibility.

Excellent!!  Any idea how an exp converter can be built out of tubes??
I've looked but I haven't found anything.  By generating its own heat, it
might be less sensitive to the heat thrown off by neighboring tubes.  I'm
glad to see that you built your circuit using 12AX7's, a popular dual
triode that grows on trees.

>I think there could be other schemes, employing heated thyratrons, but I
>don't have a source for them at the moment.

Do you think a thyratron can be made to function as a current controlled
oscillator??  I was under the impression that their response was
non-linear, and hence the need to switch between hand selected resistor
values in the Phattytron.

At 10:46 AM -0500 11/22/99, harrybissell at wrote:
>What about neon aging as the cathodes decay... and limited life ???
>does this mess up the expo conformity of just a pitch offset ???

I don't think this would have any effect on the exponential converter, or
cause any noticeable detuning while playing.  In 1957, a neon lamp was used
in the Kinsman Organ.  After they deliberately pre-aged the lamps, the
breaking voltage decreased gradually over time requiring a minor adjustment
every several thousand hours.

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