Tube Challenge!!

media at media at
Sun Nov 21 17:04:24 CET 1999

At 8:39 AM +1100 11/21/99, Paul Perry wrote:
>>Can you build an exponential converter out of tubes??
>.cerainly you can.
>This is treated in any book on analog computer design.
>See the books by G.Korn for more than you want to know.

Do you know the title??  Maybe I could do an inter-library search.  Public
libraries aren't big on electronic books, and I'm thinking any book on tube
computer design would be out of print.  Is there anything online??

>I have heard that it was john Simonton at PAiA who first called them
>'analog synths' after the analog computers. The transistorised
>analog computers of the day look like a modular synthesist's wet dream.

I'm thinking they were called "analog synths" after digital synths were
invented -- before then, they were just "synths" :)

At 12:01 AM +0100 11/21/99, Rene Schmitz wrote:
>There is something on my bench right now...
>Its a high voltage tube based current contolled oscillator together
>interfaced to  a garden variety solid state expo convertor. I don't know
>yet how stable the CCO (neon lamp) is, but the exponential control works
>fine. I'll post schematics in a few days.

Excellent!!  If it works then we can combine it with a tube exponential
converter and have an all tube VCO.  Neon lamp relaxation oscillators
aren't very stable.  The gas is temperature sensitive, and the discharge
point tends to move around erratically when the lamp is new.  When a neon
lamp was used in the Kinsman Organ -- they deliberately pre-aged the lamps.
I've read that neon lamps typically last over 10,000 hours.

At 3:08 AM -0800 11/21/99, Jonathan Lippard wrote:
>>I remember from my college electronics days that you can emulate the
>>bahavior of an inductor using an opamp and a capacitor. I dont remember the
>>specifics, but you may want to investicate this angle if you are looking for
>>a cheap/widely available alternative to inductors...
>>-Dan Gendreau
>If I may interject...I believe that something like this is given in _The
>Art of Electronics_, in the beginning of the chapter on active filters and
>oscillators (Chapter 5, I think).

I just looked.  It is in Chapter 5.  Active filters are very popular --
we're up to our eyebrows in electronics and very few things have inductors,
although I still see them in switching power supplies.  I think an entire
book on active filter design was written by that guy who hates patents.  So
while that's generally good advice, the whole point of this thread is to
build a synth out of tubes.  Once you start tossing in op-amps it's no
longer a tube circuit.  I'd like to see something simple and elegant that
can be wired point-to-point with a few components.  Imho, once you are at
the point where you are making little gyrator daughterboards, you might as
well be winding your own inductors.

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