Vacuum tube VCO with expo control.

Rene Schmitz uzs159 at
Mon Nov 22 23:08:44 CET 1999

As I used a small neon lamp for indicator purposes, like the ones found in 
many powerswitches, there are probably no radioisotopes inside. 
What you say about this effect is what I already suspected, due to
resorption of 
light the electrons have different energy levels effectively lowering the

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


At 10:46 22.11.99 -0500, harrybissell at wrote:
>Hi Rene
>Neon tube sensitivity to light is well known (well used to be...) The
light gives some ionizing energy and lowers the potential.
>There are some bulbs doped with a radioisotope that have much less
sensitivity... but I forget which ones. I'll search the old catalogs...
>But if I remember the NE-2 and NE-2H differed in this respect... don't
remember which was which though...
>What about neon aging as the cathodes decay... and limited life ??? does
this mess up the expo conformity of just a pitch offset ???
>Anyone up for revisiting the Unijunction Transistor
>:^) Harry

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