modules with different tubes?

[Mike Granger]

It is certainly possible, and I did it many times in my youth. It is easy to
use a neon lamp as the discharge element of a sawtooth relaxation oscillator,
similar to the way you would use a thyratron tube. Here is a crude circuit that
we used to drive with a 90 volt battery:

                           (1 Meg resistor)
 +90v 0----------/\/\/\/\--|--|------------|(-------0  Output Sawtooth
                                      |   |
                                      |   ----|-----
            (0.1 MFcap)   ===      |(neon bulb)
                                      |   ----|-----
                                      +-+
                                      |
                                      |
                                    Gnd (0 V)
You should be able to drive it with a voltage controlled high voltage current
source to create a voltage controlled oscillator. You need to use capacitors
that have high enough ratings to withstand the circuit voltages. The neon's are
light sensitive, so you may want to paint them black or cover with electrical
tape to shield out light.


Mike Granger


Glen wrote:

> At 07:28 PM 1/9/01 , Nick Zuccaro wrote:
> >
> >i've also got a line on the guts of a lowery organ full of
> >6x8's, which i've heard can also be made into VCOs. are there
> >any schematics out there for 6X8/12AX7 VCO circuits? the whole
> >concept of tube synthesis is extremely interesting and i'm
> >really trying to get into it, and now i have a bunch of tubes,
> >so all i really need now is to track down <or make!> some good
> >designs...thanks...Nick
>
> I might also be able to get my hands on an old organ chassis filled with
> lots of tubes of the same type. They used to use tubes for the top octave
> oscillators, and then more tubes for divider stages. Each oscillator or
> divider stage required a separate tube (or half of a dual tube). There are
> a lot of them, but as Nick said, those types don't seem to be used in any
> of the Synth-DIY circuits. I've seen organs that used quantities of 6AU6,
> 12AU7, 12AX7, etc. In addition to the oscillator and divider circuits,
> there will also be a handful of other tube types used for various functions
> on the organ.
>
> I'm also wondering, much like Nick, is there any cool Synth-DIY application
> that these can be used for?
>
> For what it's worth, there were also many old organs that used several neon
> lamps in their divider circuits, instead of using tubes. It looks a bit odd
> to open an old organ and see all that light being generated deep inside the
> console. For a my final question, would it be possible to make an
> oscillator with neon lamps? I don't expect to make a nice 1V / Octave synth
> oscillator, but at least an oscillator of some sort?
>
> Later,
> Glen