Matched transistor packages are becoming rarer and more expensive. With these 'Transistor Matchers' it is possible match your own transistors and acheive results almost as good as what you can get with the matched pair packages. The design is based on one from Moog
The design used here matches
the Vbe of transistors under constant current to within a couple of millivolts
and is a good way to find transistors that will function well in log convertors and
other non-linear circuits.
Operation of the units is fairly straightforward. Connect the outputs to a volt meter that is a 50,000 count meter
with excellent precision that can measure parts of a millivolt. Tenths of a
millivolt accuracy will work but 1/100s of a millivolt (10uV) is even better.
It is essential that the transistors to be matched are all at the same temperature and that the measurements are done in a draught free environment and with a stable temperature. Use tweezers or wear a thin nylon glove to handle transistots to be measured.
After you insert the device to test let a minute of stabilization time go by.
After the minute has passed record the voltage, place the device with its recorded Vbe to one side and continue testing other transistors. The goal is to find pairs whose Vbe match within +/-2 millivolts.