Pin Arrangements

Individual elements in vacuum tubes are connected to metal pins which penetrate the envelope. Different tubes have different number of pins. The 7- and 9- pin miniature types and octal bases are the most common. Figure 4 illustrates pin arrangements for these tubes.

Schematic diagrams or a tube manual will illustrate which tube element is connected to each pin. Some tubes have connections at positions other than the base. Tubes used in high-power circuits, such as RF amplifiers, sweep tubes in televisions and some rectifiers have plate connections at a cap on top of the tube. Circuit connection is made with a friction-fit socket. Corrosion can make these connectors difficult to remove. Care should be used to prevent the cap from breaking off or the tube envelope from cracking.