[sdiy] Temperature stable lin-exp converter with a CA3086or CA3046

[Ian Fritz]

At 10:02 PM 5/27/2002, patchell wrote:
> >
> > BTW, weren't the old Q81's made with a high-resistivity alloy (Nichrome?
> > Anybody remember?)
>
>     I have a few 2K TelLabs Q81's.  I could probably disect one to find 
> out....but
>man, it is going to be difficult to motivate myself for just curiosity 
>sakes...I
>was always under the impression they used copper (copper has the required 
>tempco),
>but, I could be wrong.

All free-electron-like metals have the correct tempco. At temperatures 
above a certain temperature (the Debye temperature) resistivity changes are 
proportional to T, according to theories by Debye and Einstein.  I have a 
beautiful figure here from a review article that shows data from Li, Na, 
Cu, Au and Pb all falling on a single curve (with appropriate 
material-dependent scaling). Alloys are more complicated, but often have 
the same linear dependence at high temperature.

Don't trash your Q81s!

   Ian