Tube Challenge!!

Bill Layer blayer at
Tue Nov 2 14:38:26 CET 1999


>  I would like to send out a challenge
>to the tube gurus out there who are "carrying the torch".

(Bill looks up..)

>Here is my challenge; I would like to see somebody come up
>with some synth DIY tube projects on a website designed for
>the tube novice. For starters, how about a VCO built
>entirely from a few common tubes (12AX7 etc.), that
>produces various waveforms, with V/Oct scaling and FM

This would be far in advance of current technology. The current vacuum tube 
VCO are sawtooth relaxation-oscillators, not capable of Sines or Triangles. 
If you can only have one waveform, sawtooth is probably the one to have. To 
do a sine oscillator, several approaches could be taken - voltage variable 
capacitances, variable inductors etc..

>  I think that this could be an incredibly
>PHAT sounding oscillator.

I guess I should make a recording of my tube VCO with a couple of (SS) 
filters applied.. The files I heard on Eric's site do not do the machine 

>So, any brave souls up to the challenge?

My time (and space) are super-limited right now, but this would be a good 
I/O project for an old computer.. See, we need a special controller for the 
Sawtooth VCO because it has a non-linear voltage response curve. We must 
build a 2-3 octave resistive step ladder and control each note with a gate 
(and step) of it's own.. This could be a simple key-contact device, or one 
under MIDI/computer control.

There was such a device for the commodore 64, that provided something like 
(256?) open-collector outputs for controlling home stuff.

PS In exchange for a beer, I'd be happy to send a 2D21 Thyratron to anyone 
building the VCO. This is the only strange tube in the circuit.

|      "The" Bill Layer - Frogtown, Minnesota. U.S.A.      |
| Vacuum tubes, Analog, Motorcycles and Other Alternatives |
+---------------------+  +---------------------------------+
| <blayer at> |  | <b.layer at> |
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