Tiny Transistors and Printed Circuits Are Important Developments in Electronics (Jun, 1952)
Tiny Transistors and Printed Circuits Are Important Developments in Electronics
TRANSISTORS, subminiature tubes and printed circuits are now being brought to the attention of the general reader, who may be amazed at their tiny size and remarkable possibilities. Most radio students and experimenters are familiar with sub-miniature tubes and the unbelievably small components used in printed circuits, especially in the manner in which they are used in hearing aids.
One of the recent subminiature-tube units is the three-tube audio amplifier illustrated in photo A. It is a complete three-stage speech amplifier built on a lightweight plate of thin ceramic. Designed for commercial and military applications where dependable amplification is required in extremely small or portable equipment, all resistors, condensers and tube sockets are included in the tiny amplifier unit, which is not much larger than a postage stamp. The actual dimensions are 1-1/32 x 15/16 x11/32 in. One of the small components used with miniature portable equipment of this description is the volume control with built-in switch shown in photo B. This is actually smaller than a dime.
The transistor is a comparatively new germanium-crystal device, more properly called a germanium triode. The germanium-diode crystal was developed during World War II and used in radar equipment. The transistor is closely related to it. The main difference between the two is that the transistor has two “whiskers” instead of one making point contact with a tiny germanium wafer. Thus it becomes a useful tube substitute in certain radio and TV-circuit applications.
This new triode unit, photo C, is an amplifier developed by the Bell Telephone laboratories and is about the size of a pea. The basic circuit is shown in Fig. 1. One of the whiskers is biased with a small positive voltage. It acts very much like the control grid of a triode tube and is called the emitter. A much higher negative voltage is applied to the second whisker which is called the collector. It is similar to the plate of an ordinary tube. The germanium crystal is the common electrode and it is comparable to the cathode of a tube. In one type, the points of the two whiskers rest upon the germanium “base” surface only .002 in. apart. A signal is applied to the input circuit in series with the low emitter bias voltage and the amplified signal is taken from the output circuit.