[2566] Inside Ge Transistors

Date: May 10th, 2019 | Comments : none | Categories: DIY.

The inside of germanium transistors can be interesting due to the differences in how they may be constructed. The Ge transistor pictured above is a common design that has a metal plate welded to one of the legs of the transistor. There is a hole in the metal plate and a germanium wafer is mounted over the hole in contact with the plate. Wires are soldered to the top and bottom sides of the thin germanium slice and connect to the remaining two legs. These are the emitter and collector. The middle pin is in contact with the metal housing but the pins on the left and right are insulated with plastic or rubber grommets installed where the pins pass through the housing.

In a different type of Ge transistor, the wafer is soldered to a stamped steel mount that connects to the metal body and the base pin. The emitter and collector pins are on each side and have very thin wires that are soldered to the doping pellets on the top side of the wafer, which are less a millimeter apart. The wires are as thin as a human hair. Inserts in the holes for the pins insulate them from the metal body.

The photo above is an AC128 transistor. While the other germaniums shown had empty housings, the AC128 is filled with a substance that appears to be heatsink grease, which has already been cleaned off the actual transistor elements for this shot.

The construction of the AC128 is similar to the first transistor shown at the beginning of this article except the base plate is mounted vertically. The germanium wafer is attached to the mounting plate and the E and C pins are connected to opposite sides of the wafer (without touching the base plate).

All of the germanium alloy transistors have a thin slice of very pure germanium that serves as the base material, which is an n-type semiconductor. On each side of the wafer is placed a pellet of indium p-type doping material. The assembly is baked in an oven so that the indium diffuses into the germanium base to make a p-type semiconductor area on each side. The result is a P-N-P transistor (from top to bottom) as shown here.


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