18-04-2016, 02:04 PM
If there are no date stamps anywhere on the cabinet or chassis or on the electrolytics, one way of dating sets fitted with Mullard valves is from the date codes etched (usually) or sometime printed - usually in black - at the base or on the underside.
A 'new' code was introduced from 1955 onwards, so fits in with this set, relying on the fact that it would be very rare indeed for every single valve in a set to have been changed in its lifetime. IF amps and audio detector/preamps usually fall into this category whilst the output valve and rectifier rarely do!
There are two lines of code, the first is a type code which should be ignored but the second line contains the date code.
It consists of three characters (4 from 1961) as follows:
The first identifies the factory and is only of academic history here. It may be a letter, number or symbol as in these examples:
Δ Philips, Copenhagen
B Mullard, Blackburn
± La Radiotechnique, Chartres
B, of course, is the most common on Mullard branded valves!
Following that is the year number and is the last digit of the year. Then there is a letter indicating the month: A = January, B = February and so on.
From 1961 a number from 1 to 5 was added indicating the week in the month that the valve was made - in fact the only thing you don't know about the valve is the name of the girl who assembled it!
Thus B7C says the valve was manufactured at Blackburn in March 1957; Δ3K2 would be a Danish valve made in the 2nd week of November 1963.
I'd check out the UF41 and UBC41 and, possibly, the UCH42 and see what you come up with!
A 'new' code was introduced from 1955 onwards, so fits in with this set, relying on the fact that it would be very rare indeed for every single valve in a set to have been changed in its lifetime. IF amps and audio detector/preamps usually fall into this category whilst the output valve and rectifier rarely do!
There are two lines of code, the first is a type code which should be ignored but the second line contains the date code.
It consists of three characters (4 from 1961) as follows:
The first identifies the factory and is only of academic history here. It may be a letter, number or symbol as in these examples:
Δ Philips, Copenhagen
B Mullard, Blackburn
± La Radiotechnique, Chartres
B, of course, is the most common on Mullard branded valves!
Following that is the year number and is the last digit of the year. Then there is a letter indicating the month: A = January, B = February and so on.
From 1961 a number from 1 to 5 was added indicating the week in the month that the valve was made - in fact the only thing you don't know about the valve is the name of the girl who assembled it!
Thus B7C says the valve was manufactured at Blackburn in March 1957; Δ3K2 would be a Danish valve made in the 2nd week of November 1963.
I'd check out the UF41 and UBC41 and, possibly, the UCH42 and see what you come up with!
