Mullard 12ax7 dating
This should make an excellent replacement for any audio application that uses the 12AX7 in the circuit.
Many prefer these to the Telefunken and are probably the second most sought after brand of 12AX7. The earliest versions from the 1950's have a "treble clef" logo or just the name Amperex (looks like the lettering above).. 1970's versions have the "world" logo in orange printing. The easisest way to tell the difference is to look at the side of the plate in the center.The 12AX7 is one of the most widely used double triodes in audio circuits. In most cases, they can all substitute for each other.I will first attempt to describe each version and provide data for each.There are many Telefunken tubes out there that don't have the Telefunken name on them, but instead an OEM brand like Fisher, H. This is true for other brand names of tubes like Amperex, etc.It has also come to my attention that there are some perfect "fake" copies produced in China which are difficult to tell from the genuine ones.
It is fairly rare to see a weak or bad Telefunken tube.