Vacuum Tube Numbering Systems

European System

First Letter indicates the heater supply	Subsequent Letters indicate the type of valve	Subsequent Numbers indicate the base1
A	4V AC	A	Single diode	20	29 B8G (Loctal)
C	200mA AC and DC	B	Double diode	30	39 Octal
D	Battery supply 1.2-
1.4V	C	Triode	40	49 B8A
E	6.3V AC and DC	D	Triode output valve	50 - 59	Miscellaneous
G	5V AC	E	Tetrode	60 - 79	Subminiature
K	2V battery supply	F	Pentode	80 - 89	B9A
P	300 mA	H	Hexode or heptode	90 - 99	B7G
U	100 mA AC and DC	K	Octode
L	Pentode output valve
M	Tuning indicator
N	Thyratron
Q	Nonode
T	Miscellaneous
X	Gas filled full wave rectifier
Y	Half wave rectifier	`
Z	Full wave rectifier

American System

First figure indicates

the heater voltage	Second and other characters are "Tube Identifier" serial numbers	Suffix letters2
0	Cold cathode	G	Large glass envelope
1	0 - 1.6V	GT	Small glass envelope
5	4.6 - 5.6V	M	Metallised
6	5.6 - 6.6V	X	Low loss base
7	6.3V Loctal	W	Military type base
12	12.6V
35	~35V

JAN tubes are Joint Army Navy tubes, and are militarized vacuum tubes.