Valve Numbers and how to decode them
European system, also known in Britain as the Mullard Code 
Two codes are used, one for transmitting and industrial valves, the other 
for receiving valves. Both consist of a string of two or three letters followed by a 
series of digits, for example  ECC83, EL34.
First letter (general class of valve)
M       LF power amplifier or modulator triode
P       RF power pentode
Q       RF power tetrode
R       Rectifier
T       RF power triode
Second letter (type of cathode)
G       Oxide-coated filament in mercury-vapour rectifier
V       Indirectly heated oxide-coated cathode
X       Directly heated pure tungsten filament
Y       Directly heated thoriated tungsten filament
Z       Directly heated oxide-coated filament (except in mercury-vapour 
Third letter
S       Silica envelope
First number (anode voltage in kV) followed by hyphen
05      0.5kV
5       5kV
12      12kV and so on
Second number (output)
For valves up to 5kW anode dissipation, the figures indicate maximum anode
dissipation in watts.
For water-cooled valves above 5kW dissipation, the figures indicate the 
output in kW.
For rectifiers, the figures indicate the maximum permissible rectified 
current per valve
in milliamps.
First letter (heater rating)
A        4V
B       180mA DC series connection
C       200mA AC/DC series connection
D       1.4V DC (normally directly heated, can also be 0.625, 1.2 or 
E       6.3V (by far the most common prefix)
F       12.6 or 13V
G       5V, later defined as ‘miscellaneous voltages’
H       150mA series connection
K       2V DC
L       450mA series connection (?)
O       cold device, not heated, e.g. cold cathode tube, voltage 
stabiliser or
        semiconductor device
P       300mA AC/DC series connection
U       100mA series connection
V       50mA  series connection
X       600mA series connection
Y       450mA series connection
The second and where applicable, third and fourth  letters in 
multi-electrode valves
indicate the types of device in the valve. They are normally listed in 
alphabetical order.
A       Signal diode
B       (=AA)  double diode
C       Signal triode
D       Output or power triode (e.g. TV shunt stabiliser)
E       Signal tetrode
F       Signal or RF pentode
H       Hexode or heptode (Hexode structure)
K       Heptode or octode (octode structure)
L       Output tetrode, beam tetrode, or pentode (including TV line 
output valves)
M       Magic eye tuning indicator
N       Gas-filled triode or thyratron
Q       Nonode
X       Full-wave rectifier or double diode (gas-filled)
Y       Half wave rectifier or single diode (vacuum)
Z       Full-wave rectifier or double diode (vacuum)
Digits indicate the base (first digit) and a code to distinguish valves 
would otherwise have identical numbers (e.g. EL84 and EL85 are both output
pentodes with a 6.3V heater on a B9A base. They are otherwise different).
1 - 10                          side contact
11 - 20                         footless
21 - 30                         Loctal
31 - 39 and 300 series          International Octal
40 - 49, 140 - 149              B8A
60, 70                          Subminiatures
80 - 89, 180 and 800 series     B9A
90 - 99                         B7G
200 series                      B10B
500 series                      B9D
GEC Code (Marconi/Osram Brands also)
Consist of Letter (or Letters) followed by digits (e.g. L63, KT88). The 
are simply to distinguish similar valves (like all triodes), and cannot be
decoded. The letters have the following meaning.
A       Industrial valve (Maybe almost anything - power triode, etc.)
B       Double triode
D       Diode
GU      Gas-filled rectifier
GT      Gas Triode (Thyratron)
H       Signal triode (high impedance)
KT      Kinkless tetrode (beam tetrode)
L       Signal triode (low impedance)
MU      Indirectly heated rectifier
N       Output pentode
P       Output triode
QP      Quiescent push-pull double pentode
S       Tetrode (Screen Grid Valve)
U       Rectifier
VS      Variable mu tetrode
W       Variable mu pentode
X       Triode hexode, heptode, octode, frequency changer
Y       Tuning indicator
Z       HF pentode
USA (Radio Manufacturers Association)
This code consists of digits, letters, digits plus an optional suffix. A 
variant is used by
the Russians.
The first digits give the heater voltage rating, with the exception that 
the codes 7
and 14 are used to indicate 6.3V and 12.6V valves  with a loctal base. 
Not all tubes
follow the rules; for instance 1F4 has 2V heaters and 2C22 has 6.3V 
Letters specify the type of valve, but there appears to be no consistency 
coding. S often indicates a single-ended (no top cap) version of an 
valve with such a cap
Second digits give either the number of active electrodes, or the number 
external connections.
The suffix letters specify the type of envelope or base. The code is
G       large Glass envelope.
GC      Glass Compact,  a tubular glass envelope
GT      Glass Tubular, the smallest glass envelope
LT      Locking base
M       Metal envelope
WA      High quality version
Mazda Code (Great Britain)
Consists of digits, Letters, digits. Do not confuse with a US code.
First digits give heater voltage, except that 10, 20, 30 indicate 100mA, 
300mA for series connection
Letters give type of valve
C       Frequency changer
D       Signal diode
F       Signal tetrode/pentode
K       Thyratron
L       Signal triode
M       Tuning indicator
P       Output tetrode/pentode
U       Half wave rectifier
UU      Full wave rectifier.
Mazda codes tend not to double up letters - L is used for multiple triodes
Final digits distinguish between otherwise identical codes.
British Royal Air Force
Code consists of letters followed by digits. The letters have the 
meanings : 
VCR - valve cathode ray (CRT)
VGT - valve gas triode (thyratron)
VI - valve indicator (tuning eye)
VR - valve receiving (general receiving valve)
VS - valve stabilising (gas stabiliser)
VT - valve transmitting (general transmitting valve)
VU - rectifier
British Army
Again, letters followed by digits. The letter part gives the valve type as
follows : 
ACR - Army CRT
AR - Army receiving valve (generally triode)
ARD - Army receiving diode
ARDD - Army receiving double diode
ARH - Army receiving hexode
ARP - Army receiving pentode
ARS - Army receiving screen grid (tetrode)
ARTH - Army receiving triode hexode
ARTP - Army receiving triode pentode
AT - Army transmitting valve (generally power triode)
ATP - Army transmitting Pentode
ATS - Army transmitting Screen Grid (Tetrode)
AU - Army Rectifier
AW - Army Stabiliser
British Royal Navy
Another letters followed by digits code. The letters give the type of the
valve, as follows : 
NC      Navy CRT
NGT     Navy gas triode (thyratron)
NR      Navy receiving valve
NS      Navy stabiliser
NT      Navy transmitting (or power)  valve
NU      Navy rectifier
Other British series
CV (common valve) numbers replaced the above 3 codes during WW2. There is 
way to decode these by simple inspection of their number.  ZA and 10E are 
also used
as prefixes to catalogue numbers. For example UHF ‘horned’ triode 10E/392 
is also
equivalent to ZA 3055, VR 135, NR 80, CV 1135 and E 1148.
French Army
Originally numbered in the TM (Télégraphie Militaire) series with the 
letters TM
followed by the type number. There was also an ‘11’ series of all-metal 
with octal base and equivalent to comparable American types but using 
heaters. Thus 11L6 was similar to 6L6 but using 11-volt heaters. Valves 
ECMR indicate French army origin (Etablissement Centrale du Matériel
Radio-télégraphique militaire.
German Defence (Reichswehr) 
Most German army valves use a special base and bear codes in the format: 
two letters,
two digits, one letter and two digits.
First letter
R        Reichswehr (Defence), includes both Wehrmacht (Army) and 
Second letter
D       Dekametric wavebands
G       Rectifier (Gleichrichter) or diode
K       Cathode ray tube
L       Transmitting or Power
V       Amplifier (Verstärker)
First number
Heater voltage
Third letter
A       Cathode ray indicator
D       Dual anode
G       Rectifier or diode
H       Hexode
L       Speed modulation
M       Magnetron
P       Pentode
T       Triode
Final number
This indicates the maximum power output in watts if the valve is a power 
tube, the
coefficient of amplification if an amplifier or maximum rectified current 
if a rectifier.
A different scheme was used by the Air Force, employing two letters and a 
The number is a simple type number, issued progressively as each new 
valve was
First letter
L       Luftwaffe (German Air Force)
Second letter
B       Cathode ray tube
D       Dekametric waves
F       Special type
G       Rectifier or diode
K       Stabiliser
M       Magnetron
S       Transmitting, wavelengths above 1 metre
V       Amplifier, wavelengths above 1 metre
Exceptions to this scheme include SA (rectifier), SD (triode) and SF 
(pentode), all
using 1.9V heaters.
Mazda (France)
Television tubes use the code letter C (for cathode ray tube), a number 
screen size in mm), then two letters followed by a number. The first 
indicates the
method of deflection (M = magnetic, S = electrostatic) and the second the 
colour (B = blue, G = green,  R = radar long-persistence, W = white). The 
were allocated sequentially.
Miniwatt (France)
This is a subset of the European system. Either two or three letters are 
used, followed
by a sequential number.
First letter (heater)
A       4V AC
B       180mA DC
C       200mA AC/DC
D       1.4V battery
E       AC and 6.3V car battery
F       13V car battery
H       4V battery
K       2V battery
U       100mA AC/DC
Second and optional third letter (type of valve)
A       Diode
B       Double diode
C       Triode (oscillator, detector, amplifier)
D       Audio power triode
E       Pentode
F       RF pentode
H       Hexode or heptode
K       Octode
L       Audio power pentode
M       Visual tuning indicator
X       Dual-anode rectifier (gas-filled)
Y       Single anode rectifier (vacuum)
Z       Dual-anode rectifier (vacuum)
Television tubes use two letters followed by a number. The first 
indicates the method
of deflection (D = electrostatic, M = magnetic) and the second the screen 
colour (B =
blue, G = green,  R = radar long-persistence, W = white). The numbers 
were allocated
Telefunken (Germany)
This simple code had just two series, RE and RS, standing for 
(receiving valves) and Röhren-Senden (transmitting valves). The 
three-digit number
following indicates first the heater current (first two digits, in 
hundredths of an amp)
then the heater voltage (4, 3, 2  or 1 for 4V, 3V, 2V or 1.5V). The final 
letter indicates
the valve base pattern,  t for Telefunken, d for Europa-base with side 
contact for space
grid, and no letter at all for Europa-base.
American Army (US Army - Signal Corps)
VT numbers are USA military valves, with  no way of decoding their 
pattern without
look-up tables, although many valves were dual-marked with VT and 
civilian part
BVA numbers (British Valve Association) were assigned to valves used for
civilian replacements in WW2.