Transistor matching method ?

[Joachim Verghese]

On Wed, 24 Jan 1996, Haible_Juergen#Tel2743 wrote:

> When I built the Moog filter, I used the Vbe matching method suggested
> by Moog. But now I often just use my multimeter to match hfe's when I
> need a pair. I really don't know if that makes sense at all. I'm quite
> sure that it's not the same, but the parameters would be dependant on
> each other somehow ... anyone who can tell me exactly?

Sometime back I did some tests on a batch of 20 2N3906s (all from
one manufacturer). I forced a known constant current into the
collector, and then measured Vbe and Ib. I also tried my best to
keep the temperature constant. Here are the values for some of the
transistors:

    Veb (mV)     Ic/Ib

1   601          150
2   601          153
3   600          158
4   598          194  (double checked)
5   598          177
6   597          179
7   596          182
8   596          187   

>From the above figures one could conclude that the two parameters
*are* correlated, but there seem to exist individuals with a hfe
higher than expected. I also tested some 2N3904s, and the results
were similar.

-joachim