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Vacuum Tube Pin Numbering

Many people beginning to work with vacuum tube equipment need to know How Vacuum Tubes (Valves) are Numbered.

Tubes are numbered in a clockwise position: however where number 1 varies depending on the socket of the tube. Here is an explanation. All images are viewed from the pin side of the tubes (if in the socket, the wiring side of the socket.

Most tube (valve) bases have some sort of key (a part sticking out from the base of the tube so you can't plug it in the socket wrong, or some indicater, such as a gap in the pins. The first pin clockwise of this orienting indicator is Pin 1. The remaining pins are numbered in a clockwise direction from pin 1. An example is the common 9-pin miniature base (as 12AX7, 12AU7, etc.) shown below:

Tube Numbering
7-pin miniatures work the same, except of course that the last pin will be pin 7. Same goes for compactrons (9- and 12-pin) and MagNoval (9-pin) types.

Octal (6L6 etc.) and Loktal (many 7xx and 14xx types) The key in the center points to the space between pin 1 and pin 8.

4-pin (e.g. 80) and 6-pin (e.g 1625) Imagine the "key" to be between the two thicker pins.

For 5-pin (e.g. 807) The key to be opposite to the pin that's off to itself. This means that this "solitary" pin is actually pin 3.

Acorn tubes, nuvistors, transmitting tubes, and other oddballs: Consult the manual for pin designation.

For more info (including pictures) of various tube bases, consult this Tube sockets site.

For details of most tubes, visit DuncamAmps

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