How to date Telefunken Valves

Genuine Telefunken Germany (Berlin and Ulm) made Valves have a diamond mark moulded into the glass between the pins. If the diamond mark is missing, the tube was likely made by Siemens or another of the Dutch Philips companies. The codes printed on the glass may be Telefunken codes, but without the diamond mark in the bottom glass the tube was not actually made by Telefunken.

Telefunken was an old German company created back in 1903. By 1906 they were building arc radio transmitters, and by 1907 were demonstrating radio transmission of music, only a year after Fessenden used his microphone to broadcast voice in the USA. By 1935 they were building the first tape recorders, along with AEG in Germany, and by 1936 were transmitting the first television broadcasts of significant power, that being the coverage of the Olympic games in Berlin. Valve codes changed from the late 1960s and beyond until the Berlin and Ulm factories shut down, the codes were as follows:

On the side of the valve there is a 7 digit code beginning with a letter B for Berlin or U for Ulm, and might end with a letter. You only need the first letter and the first 5 digits to determine the factory and the manufacture date.

For example, U9208811:

U= Ulm, West Germany

Day=reverse the first and second digit=29.

Month=third and fifth digits=08=August

Year=fourth digit is the year, 8=1968.

Therefore, we have Ulm factory, August 29, 1968.

Another example: B2009300

B=Berlin factory.

Day=reverse the first and second digit=02

Month=third and fifth digit=03=March

Year=fourth digit=9=1969

This code would then be Berlin factory, March 2, 1969.


*all information in this post was obtained at www.audiotubes.com/teledate.htm