A packaged version of the original transistor that was demonstrated in 1947 and from which the bipolar junction transistor was developed. Two point contacts – ‘emitter’ and ‘collector’ – rested very close together on a germanium (semiconductor) crystal, which in turn was soldered to a metal disc – the ‘base’. The components were housed within a metal cylinder connected electrically to the metal disc and crystal, forming the earth terminal, while the point contacts connected to pins that could be plugged into a socket. When a small signal was passed between the two point contacts, the current flowing in the device was amplified, largely due to the great difference in resistance between input and output ends. The larger output was modulated in accordance with the input signal.