Doctor_Zoidberg
Active Member
I posted this here probably 12+ years ago I think and it's probably lost in the archives by now, the info is still very useful so here it is again.
First of all this info is, to the best of my knowledge, correct BUT nothing to do with the way things were date coded in the late 50s, 60s and early 70s is ever 100% accurate (Gibson serial Nos for instance). This just might coincide with the amount of a certain resin from a particular plant that a lot of people were smoking at the time, who knows.
It may remove some of the mystery surrounding numbers on old valves.
I have posted this info on a few forums, so if you see it elsewhere please don't give me grief.
Thanks.
OK, here goes:-
Firstly there is the general valve type code:-
Mullard Code (Used for UK and European valves):
This consists of a string of letters followed by a string of digits. E.g. ECC83, EL34 First letter gives heater rating
A - 4V
C - 200mA series connection
D - 1.4V (Normally directly heated)
E - 6.3V (By far the most common)
G - 5V
H - 450mA series connection
K - 2V
O - cold cathode/semiconductor device
P - 300mA series connection
U - 100mA series connection
The rest of the letters give the types of device in the valve. They are normally listed in alphabetical order.
A - signal diode
AA - 2 diodes with separate cathode
B - double diode with common cathode
C - signal triode
D - power triode (e.g. TV shunt stabiliser)
E - signal tetrode
F - signal pentode
H - hexode/heptode (Hexode structure)
K - heptode or octode (octode structure)
L - output tetrode, beam tetrode, or pentode
M - magic eye (seeing eye ?) tuning indicator
N - gas filled triode / thyratron
Q - Nonode
X - gas-filled full-wave rectifier/double diode
Y - half wave rectifier/single diode
Z - vacuum full-wave rectifier/double diode
Digits indicate the base (first digit) and a code to distinguish valves that 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).
First digit
0,1 - misc base - P base, side contact, etc
2 - B8B Loctal
3 - International Octal
4 - B8A
5 - B9G, B9D, misc
6,7 - Subminiatures
8 - B9A
9 - B7G
The next is the manufacturing code, :-
Electron tubes: manufacturing codes and type numbers
eg = IS1 B2H3
Please read article and see image for how the code is deciphered (URL's below). Also the 3-digit code is case sensitive.
The first two characters of the three-character code (Remember, this is case sensitive) indicate the valve's type: IS = GZ37.
The third character is the revision number, which would be incremented when the valve underwent a design change of some sort: 1 = revision 1 of the GZ37 design.
The first character of the four-character code indicates the factory in which the valve was made: B = Mullard's factory at Blackburn in the UK.
The next three characters, in order, are:
The last digit of the production year: 2 = (probably) 1962.
The production month (A = January, B = February, etc.): H = August.
The week number in the month the valve was made: 3 = third week (of Aug).
See the info on here for further details:-
factory codes.jpg
Additional info : -
Factory codes for UK valves with CV numbers.
All the UK military spec valves that were used by the War Department all had a CV (Common Valve) number and have always had a strange code inked on to the glass usually in the form of KB followed by a slash ( / ) followed by one or two letters i.e. KB/DA (I have also seen just the slash followed by a one or 2 letter code). This code as always been a mystery to me but the other day I was looking through some old copies of The Radio Constructor (ranging from 1951 to 1959) that a friend of mine had had inherited some 15 years ago and had given them to me and inside one was hand written in pencil the following : -
KB/AD Thorn-AEI (Brimar) Rochester
KB/D Mullard Radio Valve Co. Mitcham
KB/DA Mullard Radio Valve Co. Blackburn
KB/F STC (Standard Telephone & Cable Co.) Paignton
KB/FD STC Rochester
KB/FE STC Oldway
KB/FB STC Footscray
KB/N STC (before 1952) Footscray
KB/K Electronic Tubes High Wycomb
KB/L M.O. Valve Co. (Before 1952)
KB/Z M.O. Valve Co. Hammersmith
KB/ZA M.O. Valve Co. (Before early 1957) Gateshead
KB/Q English Electric Valve Co. Chelmsford
KB/R Ferranti Moston
Cant verify if they are all correct but the KB/DA checks out with my box of CV492s, which are factory stamped 12AX7XL, B6K2, I63.
Its stuff I have posted in the past, so it will save you trawling back through 15 years+ of posts.
Hope this is useful to someone.
Cheers
DocZ
First of all this info is, to the best of my knowledge, correct BUT nothing to do with the way things were date coded in the late 50s, 60s and early 70s is ever 100% accurate (Gibson serial Nos for instance). This just might coincide with the amount of a certain resin from a particular plant that a lot of people were smoking at the time, who knows.
It may remove some of the mystery surrounding numbers on old valves.
I have posted this info on a few forums, so if you see it elsewhere please don't give me grief.
Thanks.
OK, here goes:-
Firstly there is the general valve type code:-
Mullard Code (Used for UK and European valves):
This consists of a string of letters followed by a string of digits. E.g. ECC83, EL34 First letter gives heater rating
A - 4V
C - 200mA series connection
D - 1.4V (Normally directly heated)
E - 6.3V (By far the most common)
G - 5V
H - 450mA series connection
K - 2V
O - cold cathode/semiconductor device
P - 300mA series connection
U - 100mA series connection
The rest of the letters give the types of device in the valve. They are normally listed in alphabetical order.
A - signal diode
AA - 2 diodes with separate cathode
B - double diode with common cathode
C - signal triode
D - power triode (e.g. TV shunt stabiliser)
E - signal tetrode
F - signal pentode
H - hexode/heptode (Hexode structure)
K - heptode or octode (octode structure)
L - output tetrode, beam tetrode, or pentode
M - magic eye (seeing eye ?) tuning indicator
N - gas filled triode / thyratron
Q - Nonode
X - gas-filled full-wave rectifier/double diode
Y - half wave rectifier/single diode
Z - vacuum full-wave rectifier/double diode
Digits indicate the base (first digit) and a code to distinguish valves that 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).
First digit
0,1 - misc base - P base, side contact, etc
2 - B8B Loctal
3 - International Octal
4 - B8A
5 - B9G, B9D, misc
6,7 - Subminiatures
8 - B9A
9 - B7G
The next is the manufacturing code, :-
Electron tubes: manufacturing codes and type numbers
eg = IS1 B2H3
Please read article and see image for how the code is deciphered (URL's below). Also the 3-digit code is case sensitive.
The first two characters of the three-character code (Remember, this is case sensitive) indicate the valve's type: IS = GZ37.
The third character is the revision number, which would be incremented when the valve underwent a design change of some sort: 1 = revision 1 of the GZ37 design.
The first character of the four-character code indicates the factory in which the valve was made: B = Mullard's factory at Blackburn in the UK.
The next three characters, in order, are:
The last digit of the production year: 2 = (probably) 1962.
The production month (A = January, B = February, etc.): H = August.
The week number in the month the valve was made: 3 = third week (of Aug).
See the info on here for further details:-
factory codes.jpg
Additional info : -
Factory codes for UK valves with CV numbers.
All the UK military spec valves that were used by the War Department all had a CV (Common Valve) number and have always had a strange code inked on to the glass usually in the form of KB followed by a slash ( / ) followed by one or two letters i.e. KB/DA (I have also seen just the slash followed by a one or 2 letter code). This code as always been a mystery to me but the other day I was looking through some old copies of The Radio Constructor (ranging from 1951 to 1959) that a friend of mine had had inherited some 15 years ago and had given them to me and inside one was hand written in pencil the following : -
KB/AD Thorn-AEI (Brimar) Rochester
KB/D Mullard Radio Valve Co. Mitcham
KB/DA Mullard Radio Valve Co. Blackburn
KB/F STC (Standard Telephone & Cable Co.) Paignton
KB/FD STC Rochester
KB/FE STC Oldway
KB/FB STC Footscray
KB/N STC (before 1952) Footscray
KB/K Electronic Tubes High Wycomb
KB/L M.O. Valve Co. (Before 1952)
KB/Z M.O. Valve Co. Hammersmith
KB/ZA M.O. Valve Co. (Before early 1957) Gateshead
KB/Q English Electric Valve Co. Chelmsford
KB/R Ferranti Moston
Cant verify if they are all correct but the KB/DA checks out with my box of CV492s, which are factory stamped 12AX7XL, B6K2, I63.
Its stuff I have posted in the past, so it will save you trawling back through 15 years+ of posts.
Hope this is useful to someone.
Cheers
DocZ
Last edited:
