Pro-Electron/Mullard Code

This are probably the most commonly encountered numbering system in the UK – and the most informative. It consists of two or more letters followed by a number (normally two digits). Examples – UL41, ECC85, UABC80.

The first letter gives heater rating.

Character Heater Rating

A 4V
B 180mA
C 200mA
D 0 – 1.5V (previously 1.4V)
E 6.3V
F 12.6V
G Misc. (previously 5V)
H 150mA
K 2V
L 450mA
P 300mA
T 7.4V
U 100mA
V 50mA
W 600mA
X 450mA

The remaining letters give the types of device in the valve. They are normally listed in alphabetical order.

Character Device Type

A Signal Diode
B Double Diode
C Signal Triode
D Power Triode
E Signal Tetrode
F Signal Pentode
H Hexode or Heptode (Hexode type)
K Octode or Heptode (Octode type)
L Output Tetrode or Pentode
M Magic Eye (Tuning Indicator)
N Gas-filled Triode (Thyratron)
Q Nonode
X Gas-filled Full-wave Rectifier
Y Half-wave Rectifier
Z Full-Wave Rectifier

The first digit indicates the base type. Where there is only one digit this is assumed to be the second digit, and be preceded by a zero. For example, EM4 should be interpreted as EM04.

Digit Base Type

0 and 1 Miscellaneous Bases (P-Base, Side Contact etc.)
2 B10B (previously B8B/B8G (Loctal))
3 International Octal (8-pin with centre locating spigot)
4 B8A (8 pin with locating pip on side)
5 B9G and B9D (wire ended)
6 and 7 Subminiatures
8 B9A (9-pin glass)
9 B7G (7-pin glass)

The remaining digit(s) are used to differentiate between valves that would otherwise have identical numbers:-

One digit for early valves
Two figures for later entertainment valves
Three or Four figures for later professional types

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