Dave, if it has a B9G base, I'll bet on it being an EF50. (I only bet on certainties!)
If, on the other hand, it has a B9A base, and came from any factory in the Philips empire, identification is easy!
Just above the base you should see two rows of characters etched into the glass. The first identifies the valve type number and the second tells you the place and date it was manufactured - for example, B3C4 tells you that it was manufactured at Mullard's Blackburn factory in the 4th week of March, 1963.
To translate the first row of characters into a familiar type number you will need to consult this handy document.
Now you will know everything about your valve there is to know except the name of the girl who assembled it!
If, on the other hand, it has a B9A base, and came from any factory in the Philips empire, identification is easy!
Just above the base you should see two rows of characters etched into the glass. The first identifies the valve type number and the second tells you the place and date it was manufactured - for example, B3C4 tells you that it was manufactured at Mullard's Blackburn factory in the 4th week of March, 1963.
To translate the first row of characters into a familiar type number you will need to consult this handy document.
Now you will know everything about your valve there is to know except the name of the girl who assembled it!
