Before revision: A brief summary of just the more common letters is: ECC81 / \ \\__ last digit(s)=serial number / \ \__ first digit(s)=base (3= octal/ 8,18,80=Noval (B9A), 9= Miniature 7-pin (B7G) .
After revision: A brief summary of just the more common letters is: ECC81 / \ \\__ last digit(s)=serial number / \ \__ first digit(s)=base (3= 8pin 8,18,80=Noval (B9A), 9= Mini 7-pin (B7G)