Telefunkin I.D.

[canton]

I have found a few Telefunkin tubes trying to identify them. They name and West Germany is on them but no numbers to be made out. Any way to find out if they are 12AX7s AU 7s AT 7s? someone once said put them in a freezer and the number will reappear but I never did that sounded like what? Anyhow any help appreciated. They do have the diamond on the bottom of the glass.

 

[Dswankey]

Telefunken not Telefunkin,

Here's a pic of what a 12AX7 would look like. I've read here that if you blow on them like you might on a pair of eye glasses, the mist might reveal the numbers.

Some nice resources regarding Tele 12AX7's

http://www.tube-classics.de/TC/Tubes/SieTel ECC83/ECC83.htm

http://tctubes.com/telefunken-date-codes.aspx

 

[Tom Bavis]

12AT7s have a much smaller and shorter plate, usually folded (only one seam). 12AU7 and 12AX7 use the same plate (and you can't see the grid inside, which is the difference...). 12AX7s will test quite weak if tested as 12AU7.

 

[zackthedog]

...and conversely, a 12AU7 will read way over spec if tested as a 12AX7. ;-). I have a number of old Telefunken 12AU7s and 12AX7s with the writing worn off, and that's the only way I've been able to tell the difference.

 

[canton]

Thanks that is some good information that will help a lot today. It is time I started sorting these tubes out and putting them in MARKED boxes not just in the box.