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I have just received an e-mail asking for details of military valve markings so here's a little primer for anyone who might have a similar interest.

Valves used by the British military Armed Services were marked with a  CV or common valve name which was defined by the  Inter-Service Technical Valve Committee in 1941.     Often, below the CV number a two part  alpha code of the form KB/xx  or JB/xx will be seen  which gives the devices manufacturing specification and qualification .  For the first part of the alpha code, the K designates a valve manufactured to specification K1001 or K1006; similarly a J designates a valve manufactured to a JAN or MIL spec.  The second letter of the first part of the alpha code describes the qualification approval the valve type has, a B denotes qualification by a UK authority, a U denotes US qualification,  a D  denotes Australian qualification and an X  denotes Director of Electronics Research and Development  (DERAD)  approval.

The second part of the alpha code identifies the factory that manufactured the  device, the most commonly seen codes and their corresponding manufacturers are:- 

A Mullard, Blackburn, pre Jan 1951
A Thorn, Tottenham, pre April 1964
AB Sylvania-Thorn, Enfield
AC Brimar - Thorn-AEI, Footscray
AD Brimar - Thorn-AEI , Rochester
B Edison Swan, Baldock, pre Sept 1945
BA AEI, Woolwich
BC Joseph Lucas, Birmingham
C Edison Swan, Ponders End, pre Sept 1951
CC Cathodeon, Cambridge
CE 20th Century Electronics, pre  March 1957
CF 20th Century Electronics, New Addington
CN Pye Industrial Electronics
CO Newmarket transistors, Newmarket
CS Cathodeon, Southend
D Mullard Radio Valve Co., Mitcham
DA Mullard Radio Valve Co., Blackburn
DB Mullard Radio Valve Co., Salford
DC Mullard Radio Valve Co., Whyteleafe
DE Mullard Radio Valve Co., Fleetwood
DF Mullard Radio Valve Co., Waddon
DG Associated Semiconductor Manufacturers, Southampton
DH Societe Anonyme Philips, Brive, France
DJ Wiener Radio Werke, Abbeygasse 1, Vienna
DK Philips GMBH, 140 Ebentalstrasse, Klangenfurt
DL NV Philips Gloeilampenfabrieken, Nijmegen
DM NV Philips, Stakskanaal, Holland
DN La Radiotechnique, Caen, France
DP Valvo GMBH, Hamburg, Germany
DQ Philips SpA, Milan, Italy
DR Philips AG, Zurich, Switzerland
E Thorn-AEI, Brimsdown
EA Edison Swan, Ponders End
EB Edison Swan, Gateshead
EC Edison Swan, Tottenham
EN Thorn-AEI, Sunderland
F STC, Paignton
FB STC, Footscray
FC STC, Lorenz,. Esslingen, Germany
FD STC, Rochester
FDA Alexandria, NSW, Australia
FE STC, Oldway (Additional to Paignton factory 'F')
FF STC, Harlow
G Ericsson, Beeston
GA (Ericsson), AB Svenska Elektronror, Stockholm, Sweden
H Hivac, Harrow
HC Hivac, Chesham
HR Hivac, Ruislip
J STC, Crewkerne, pre Jan 1946
J Radar Electronic Equipment
JA SGS Fairchild, Ruislip
JB SGS Fairchild, Agrate, Milan, Italy
JD Elliott Bros. (London) Ltd, Borehamwood
JE Elliott-Litton, Borehamwood
JK La Radio Technique, Suresne, Paris, France
JN International Rectifier Co., (GB) Ltd, Oxted
JQ Associated transistors, Ruislip
JT Microwave Associates Ltd, Luton
K Electronic Tubes, High Wycombe
L CSF, Levallois-Perret (Seine), Paris, France
L MOV Highgrove pre Oct 1951
LB CSF, St. Egreve, Grenoble, Isere, France
M Gramophone Co., Hayes
MA EMI research labs, Hayes
MB EMI research labs, Ruislip
ME EMI, Hayes
MR EMI (Valve Division), Ruislip
MT EMI, Treorchy
N Nore Electric, Southend
N STC, Footscray, pre August 1951
NP Texas Instruments, Dallas Road, Bedford
NQ Texas Instuments, Bedford
NR Texas Instruments, Nice, France
O Rank Cintel, Lower Sydenham
OR Rank Cintel, Rotunda
OS Rank Cintel, Sidcup
P Philips, Eindhoven, Holland
P GEC, Shaw, pre August 1948
PA Philips Teleindustri, Stockholm, Sweden
PDA Philips, Hendon, Australia
Q English Electric Valve Co., Chelmsford
QB Marconi Wireless Telegraphy Co., Great Baddow
QC Marconi Wireless Telegraphy Co., Chelmsford
QD English Electric Valve Co., Stafford
QE English Electric Valve Co., Kidsgrove
QF English Electric Valve Co., Nelson Research Labs, Hixon
R Ferranti, Moston
R Ferranti, Gem Mill Oldham, pre July 1947
RA Ferranti, Edinburgh
RB Ferranti, Dundee
RC Ferranti, Chadderton, Oldham
S AEI, Rugby
SA AEI, Lutterworth
SB AEI, Lincoln
SC CFTH, Usine de Joinville, Seine, france
SD SESCO, Rue de L'Amiral, Mouchez, Paris, France
SDA Amalgamated Wireless, Australia
SF CFTH, Rue Mario-Nikis, Paris, France
SL AEI, Leicester
SP AEI, Peterborough
T British Tungsram, Tottenham
U MOV, Bulmer, pre Oct 1945
U Nucleonic and Radiological, Stratford
V Cossor, Highbury, pre Sept 1945
V Gilbert Photoelectrics
VA Westinghouse, Chippenham
VF MCP Electronics, Alperton
VL Hughes Internations (UK) Ltd., Glenrothes
VR Brush Rothermell Crystal Co., Hythe
W GEC, Hirst Labs, Wembley
WB GEC, Coventry
WD Claude General Neon Lights, Wembley
WE ASM Ltd, Hazel Grove
WF ASM Ltd, Broadstone
X MOV, Springvale, pre Oct 1951
Y MOV, Moray, pre April 1945
YA Leigh Electronics, Havant
YC Semiconductors Ltd., Cheney Manor, Swindon
YD Semiconductors Ltd., Towcester
Z MO Valve Company, Hammersmith
ZA MOV, Gateshead, pre March 1957
ZB MOV, Perivale
ZC MOV, Springvale, pre August 1957
ZD MOV, Dover, pre Dec 1956
ZE Osram GEC Lamp Works, MXT Dept, pre March 1957

In a separate cartouche there often is a two character alpha code which denotes manufacture date   eg AA.    The first letter denotes the year and uses the entire alphabet except for I and O  and started in 1945.  Hence an  A denotes 1945 and Z denotes 1969.    In a similar fashion the second letter denotes the month of manufacture with A  denoting January and M denoting December.

An additional system of dating is also used which records the date of valve labelling, this dating system utilises a four digit numeric code in which the first two integers denote year and the second two integers the week of the year.   Hence 6712 would denote March 1967.

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