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
. The remaining pins are numbered in a clockwise
from pin 1. An example is the common 9-pin miniature
base (as 12AX7, 12AU7, etc.) shown below:
|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.
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
For details of most tubes, visit DuncamAmps