MULLARD VALVE ETCHED CODES - HOW TO INTERPRET THEM
Posted by STEVE M on
There is much conflicting fokelore on the internet about the Mullard etched valve codes so I thought I would add our two penny-worth.
The etched codes have value to us today as they contain two discrete nuggets of information; firstly, should a valve loose it's printing you can identify the valve type and secondly, you can glean the production site and the month and year of manufacture.
The etched codes, in general, comprise of two lines stacked vertically with the top line being a three character Engineering Code with the third digit signifying the development iteration of the valve. For example, I6x signifies an ECC83 with the sequential progression off x ie. I61; I62; I63; I64 signifying production changes which may be support rod metallurgy, getter support type, pin construction, anode coating reformulation, etc - unfortunately no definitive guide to these iterations exists to my knowledge. As Mullard made 8600 different types of valve, I am not going to try and list all of the Engineering Codes but a poll of t'Interweb should find a list somewhere
The lower line is the date code and a handy decade split can be made from the number of characters this line possess: -
If its a 3 character code, the valve was produced pre 1960
If its a 4 character code, the valve was produced post 1960
The first character gives the production site and some of the most common are given below:-
B : - Mullard, Blackburn
D: - Valvo, Hamburg (Germany)
G : - Mullard, Fleetwood
J : - Mullard ( British Tungsram), Tottenham
R : - Mullard, Mitcham
X : - Philips, Sittard (Holland)
Y : - Philips, Sittard (Holland)
9: - Philips, Heerlen, (Holland)
Of course there are even more:...............
And then some more too: ......................
The second character gives the year of manufacture with decade differentiation being by number of characters and logo shape.
0: - 1950, 1960, 1970
1: - 1951, 1961, 1971
2: - 1952, 1962, 1972
3: - 1953, 1963, 1973
4: - 1954, 1964, 1974
5: - 1955, 1965, 1975
6: - 1956, 1966, 1976
7: - 1957, 1967, 1977
8: - 1958, 1968, 1978
9: - 1959, 1969, 1979
The third character gives the month of manufacture.
A : - January
B : - February
C : - March
D : - April
E : - May
F : - June
G : - July
H : - August
I : - September
J : - October
K : - November
L : - December
The fourth character gives the week of manufacture
1: - week 1 of month
2: - week 2 of month
3: - week 3 of month
4: - week 4 of month
5: - week 5 of month
To illustrate the above, here are a couple of worked examples: -
Xf2 B9H3 represents an EL34, Blackburn manufacture, week 3 of August 1959
k61 B63 represents an ECC82, Blackburn manufacture, week 3 of March 1956
f32 R9D5 represented a GZ34, Mitcham manufacture, week 5 of April 1969