Re2: Vacuum tube VCO with expo control.

Rene Schmitz uzs159 at
Tue Nov 23 00:48:18 CET 1999

At 10:46 22.11.99 -0500, 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 ???

As the thresholds will only change the linear mA/Hz scale factor of the CCO
(which ideally should go straight thru the origin) any ageing of the neon
tube should only result in a pitch shift. Current doubling still means
frequency doubling. 
Of course such long term effects aren't *very* annoying. 
But if this happens on a short time scale, it will be a pain. Hence
and light sensitivity will be probably the dominating short term effects
for detune. 
I'm yet not really convinced by the practicability of such a VCO, but time
will tell.
The heat from the tube could disturb the expo convertor, messing up the
scale. Therefore its best to place them apart. The tube however doesn't get
very hot, I can touch it without pain. (Don't do that with the anode supply


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