I found a datasheet on the Tyco website which refers to two types with a temp coeff. of 3000 and 3300 ppm.
André, en tout cas merci pour l' info ...
--- In motm@yahoogroups.com, Andre Majorel <aym-htnys@...> wrote:
>
> On 2010-05-03 12:12 -0000, peter_ivens wrote:
>
> > A tempco with a temp. coeff. of 3500 , 1K 1%, is not so
> > difficult to find. Most moduls of MOTM use a tempco of 3500 ppm
> > (like the MOTM-300) but in the BOM for the 440 & 485 there is
> > specified 1K 1% 3300 ppm.
>
> I don't think it matters much. The tempco of the circuit is
> an approximation anyway, because there are other sources of error
> than the transistor pair. And so is the tempco of the actual
> resistor because it varies with temperature (and possibly from
> device to device).
>
> If anything, it's preferable to have a resistor with too high a
> tempco because you can always reduce it by wiring an ordinary
> metal film resistor in parallel (metal film resistors have tempcos
> like 50 or 100 PPM/K).
>
> Check Ian Fritz's "dial-a-tempco" page for a really refined
> treatment.
>
> > Elby design delivers a second resitor to lower the temp. coeff.
> > but then you can take also a tempco with a tolerance of 5% from
> > Tyco.
>
> Tycos are cheap but aren't they 3000 PPM/K ? The Akaneohm sound
> like a much better deal. Or the Panasonic SMT if you're prepared
> to some kludgery.
>
> --
> André Majorel http://www.teaser.fr/~amajorel/
>