Tiny ovens

[Jim Shearer]

In message <970429091230.ZM3364 at devh8.ansys.com>, Steve Jones
<sj2393 at ansys.com> writes
>I have seen this debated/discussed here and in the
>archives, but I'm not sure I've ever been able to pull
>out any consensus (what else is new 8^).
>
>The old problem: oscillator drift due to temperature
>change.
>
>An assumption (however reasonable): no 726's.
>
>An oft proposed solution: little transistor ovens.
>
>Is the following feasible/reasonable?
>
>I'm tentatively planning my VCO.  I'm thinking of using
>a transistor array; one of those including a diff pair.
>I'm considering epoxying an inverted (physically) power
>transistor and a thermistor to it's top.  The thermistor
>would be part of a voltage divider feeding a comparator
>(w/ hysteresis).  This comparator would then be used to
>drive the heater-transistor.  The threshold would be set
>to a level just hotter than the hottest normal running
>temperature of the array.
>
>Is the epoxy heat conductive enough?  Am I oversimplifying
>this or should this work?
>
>steve

Hi Steve,
         No need to get so complicated :) why not use some of the
trannies in the array itself? they are all very closely matched and in
very close thermal contact (being on the same die). Moog used this on
their Prodigy synth using CA3046's. These are 5-transistor npn arrays
with 2 being internally connected as a differential pair, and two used
as heater and regulator (One is left unused).
   (I like the Prodigy, better sounding than the multimoog IMHO!)
-- 
Jim Shearer