We have a Vu-Data Model 5110 Semiconductor Test Set that is a real dandy. Too bad these gems are not made anymore. Here are some tips from a Vu-Data Model 5110 manual from 1985.
1. GERMANIUM TRANSISTORS - Nearly all germanium transistors come in metal cases, either in the tubular type with flexible leads or in the standard TO-5 package.
2. POWER TRANSISTORS - Power transistors in TO-3, TO-5, or stud packages can be either germanium, silicon, or FET. Two or three digit 2N-numbers are mostly germanium.
3. The TO-66 power transistors and the plastic tab packages are nearly always silicon. The Collector is usually, but not always, connected to the mounting tab and the center lead. Verification can be accomplished by a continuity check between the collector pin and the mounting tab.
4. The Base lead of most modern plastic-type transistors is either the center lead or the right-hand lead when facing the flat side with the leads down. In the latter case, the Collector lead is the center lead.
5. FETS - Most plastic FETs have the Drain lead on the right side when facing the flat side with the leads down and the Gate in the middle, but there are exceptions. In nearly all junction FETs, the source and drain can be interchanged without adverse effects.
6. POWER FETS - Power FETs in TO-3 packages generally have lead configurations similar to bipolar transistors, as follows:
Drain Collector (Case)
7. GERMANIUM SIGNAL DIODES - These usually can be identified by their transparent hollow glass cases with either three or four color bands, or numbers printed on them.
8. SILICON DIODES - These are usually painted because silicon is light sensitive and must be protected. The banded end is the Cathode.
9. All transistors will have some gain with the Collector and Emitter leads interchanged, with the exception of Darlingtons.