Tempcos

[Christopher List]

>     I have a couple of these "tempermental tempco's" here, and I haven't 
>     had the chance to figure out what the darn deal is with them. They 
>     look good on an ohmmeter (2K exactly) no matter how much fingering 
>     they get. Sure enough, put them in a VCO and it goes to pot.
>     
>     Does anybody have the manufacturer's data sheet for these weirdos?

>     So - apparently my old Q81s are "good" tempcos, and the new crop that 
>     are being supplied these days are "bad"? Maybe we forgot to specify 
>     something when we ordered them? How complicated can it be? I'm 
>     stumped. Okay here's an idea - I'll dig through all my Electronotes 
>     and try to find some disseration on tempco's. If anybody can find any 
>     engineering data on tempco's, please post!
     


I called KRL. 
The wacky tempcos that I ordered (and that Gene has) are "538Q";
3500ppm/C, .5%, 2K....  "Molded"

The ones that seem to work for people are also from KRL and are part # "C-2AQ";
3500ppm/C, 1%, 1K.... "Conformally Coated"

They say the coated vs. molded factor <<should be>> the only thing that makes 
them different. They CAN make C-2AQ types in 2K value. They don't have any 
laying around, so they are hesitant to make some up for samples because they 
can't figure out why one would be different from the other. Their tech guy is 
going to do some inductance tests tommorow to see if they behave differently in 
_that_ regard. I'd like to try a C-2AQ in the electronotes Tri-Square VCO 
(halving the input summing resistor to make up for the 1K tempco value) and see 
if it works. If it does I'd have a good reason for them to make me a 2K sample, 
and if that works then our problem is solved. I can tell KRL is not pleased 
with the idea that the 538Q would behave differently from the C-2AQ, but, if 
that's the way it is, that's the way it is...

I'm also going to test the resistance of the 538Q by REALLY heating it, just 
for laughs...

- Chris