12AX7 TF with diamond and ribbed top

[buickguy62]

I've had some 12AX7's with a Telefunken silkscreen that were obviously Philips/Siemans, but I've never had, until now a Telefunken with the 'molded in the base diamond' and four ribbed (Phillips/Mullard/ Amperex,etc.) top. Every TF I've ever seen has a smooth top. These are not some recent counterfeit, they were in a vintage Fisher 400 that was stored for decades. Total of four of these tubes. Anyone ever run across this before?

 

[Dswankey]

Maybe this will help, on the first link if you click on the pictures they will expand

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

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

http://audiokarma.org/forums/index.php?threads/help-identify-these-telefunken-12ax7s.308744/

 

[elcoholic]

Ribbed for pleasure? Hopefully they don’t sound too constrained