[sdiy] Tempco vs. "Substrate Oven" in VCO and VCF

[sleepy_dog at gmx.de]

Hey there,

first a question about thermistors (this is what "tempco" are, correct?)
In circuits for voltage control of a VCO or VCF which use a tempco, how 
much could one deviate with the coefficient, say for instance in Thomay 
Henry's newest VCO based on the TLC555 timer? I think it was spec'd at 
3500 - what if I could get one with 3470 or 3600 more easily?

Also, I find Rick Jansen's Moog VCF schematic interesting, which uses 3 
remaining transistors in a 3046 transistor array as a controlled "oven" 
for the NPN matched pair, to get rid of temperature sensitivity.
How come I don't see this kind of solution more often? Is the tempco 
solution "better"?
How much current will the "oven" draw, and does this reduce the lifetime 
of the IC?


Regards,
Steve