uA726 replacement, CEM 3340, etc.

[tomg]

Hi Harry, Paul H. and List...

The heater discussion again huh?? Ok I'll bite.....VCOs drift. I don't care
what you do to them they drift. You can hook them to a cpu and correct 
but they still drift. Tempcos work to some degree, recovery is sloooooow 
or non-existent if you throw a thermal shock at them. Not to mention
they are hard to come by and expensive if compared to the cost of a
3046. 

Heaters also work to some degree, recovery is much faster and always
occurs even when tortured. The difference between temp-controlled or
"oven" types modeled after an-299 and my "hot-chip" scheme is the hot chip
actually stays the same temperature over a long period of time and there is no 
compairator switching 25-35ma in and out next to my vco. It's at least as
good as the an-299 scheme. I had a lot of examples to go by and could
not find anything I though worked any better....or I would have used it. I
really don't like the heater idea much, I'm just not smart enough to come
up with anything I like any better....Yet!

I used a digital baby thermometer to measure the temp-differences before I
committed to the design. Later I found a terrific digital meat thermometer
that confirmed my findings at normal operating temperatures. Temp-drift
was less than 1% over a 8 hour range. Way less but I am using a meat
thermometer so 1% will do.

Gene Z. gave me a method to measure chip-tempco so I wouldn't need
to buy a thermometer and even though it worked out I felt better after
seeing the digits.

-tg