Point-contact transistor. The gold foil is split into two parts at the vertex of the plastic wedge, and forms two separate contacts with the p-type upper layer of the germanium substrate when the wedge is pressed against it by the spring. The two pieces of gold foil form the collector and emitter, and a metal electrode attached to the other side of the semiconductor forms the base electrode.
This vector image includes elements that have been taken or adapted from this file:
忍者猫  (original), Vladimir Solovjev (translate)