Heated expo-converters

[Tony Clark]

I've got a question or two for those of you that might have already tried 
this...

   I've been mucking around with a MAT-04 and the AN-299 article from 
National, trying to make a heated exponential converter out of it and 
haven't had much luck.  Well, that is, I have and I haven't.
   My first problem is that it doesn't track worth a hill of beans.  Well 
that is, it doesn't conform to 1V/Oct.  I guess I'll have to go back 
through the circuitry to find out where I goofed.
   My main problem is that I don't think the heating regulation circuitry 
is doing anything.  In fact, I can't tell that the chip is dissipating 
any heat at all.  But boy does that current limiting resistor though!  In 
fact, I am too scared to put a 33 Ohm resistor in there because a couple 
of 470's in parallel sure do get hot!
   I'm tempted to just slap two or three 470s over top of the chip and 
create a nice little thermal shield for it!
   Okay well let's see, the heater is in two parts, the heater element 
and the regulator.  The regulator should turn off the heater when it gets 
hot enough and turn it back on when it cools enough.  Mine ain't doing 
it, so maybe there's another problem.  But then I "still" don't think 
that the chip is warming up.
   Anyone got some advice?

   Thanks in advance,

   Tony

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I can't drive (my Moog) 55!
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Tony Clark -- clark at andrews.edu 
http://aupe.phys.andrews.edu/~clark
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