[sdiy] mached transistors

[Grant Richter]

Here is a useful technique.

Take a large sheet of antistatic foam. Buy a sheet of self sticking labels
1.5" x 0.75" or so in size. At the top write numbers from 580 to 620 in
steps of 1. On either side write N and P. Stick the labels to the foam at
about 1 inch horizontal intervals and in vertical rows.

Pick an afternoon with nothing better to do, and measure your NPNs and PNPs
sticking them into the foam at the voltage measured and by the appropriate
letter.

Now you can have any combination of matched PNP or NPN or both as needed.
This all has to be done at one time because it only counts for a single
temperature. Depending on the temperature of the room, you may need to make
labels that go above or below 620 or 580.
> 
> I generally try to match to 1mV.  What I do is set up to measure a whole
> bunch at one time.  I try to do this when the temperature in the room isn't
> changing (as this will through the voltage value off).  I write down the
> voltage for each transistor.  When I am done, I look at the list and start
> matching.  Transistors with the "same" value get matched.  Generally, I have
> found that in a batch of 30 transistors, I can generally get at least 13
> pairs,
> sometimes I even get 15 pairs when I am lucky.
>