AW: Re: Matching transistors

[Haible_Juergen#Tel2743]

> > transistor pairs, each wrapped in copper - and matched to a high degree
> > of precision to boot.
>
> I actually measured Vbe of all the five PNP pairs of four 4075 units
> (40 transistors, ouch!), and I was shocked by the degree of matching the
> devices had been selected for.
>
> The older 4075s with PNPs marked "ITT21172" especially had well matched
> pairs. In fact, so good that my Fluke 75 wasn't accurate enough to
> show any mismatch at all, so I had to get a better DVM. The newer 4075s
> with 2N5087s showed a worst-case mismatch of around 0.3 mV.

Impressive indeed. I started to think what a *temperature* difference
would be enough to give 0.3mV (with ideally matched transistors).
Well, I guess when you measured them, they were still wrapped into
this copper, but imagine how ARP would have matched them, *before*
they were tied thermally together ...

Maybe they put a poor tech into a room that was heated to 37 degrees,
so that touching the transistors would not make a difference anymore
 - who knows! (;->)

JH.