IEC 60135: Electronic Tube Electrode Numbering — The Vacuum Tube Equivalent of Chip Pin Definitions

Electronic Tube Electrode Numbering — One Number Determines the Socket Wiring Sequence

IEC 60135 specifies electrode numbering rules for electronic tubes and valves. A tube base has 4–14 pins (depending on type), each connecting to a specific electrode — anode, grid, cathode, heater. The numbering rules ensure that the same tube type from any manufacturer inserts into the same socket and works.

Numbering rules: Pin 1 counting clockwise from the bottom view (opposite to most connector conventions). Pin 1 is typically blank (keying reference). Miniature tubes (Noval B9A): heater typically pins 4/5, anode pin 7 or 9. High-power tubes may have a separate anode cap (top metal cap) — because anode voltage can reach several kV and cannot share the base with other electrodes.