My advice is seek out a seller that has a reputation for selling tubes with lots of positive feedback.
Be sure specifications are included in seller description such as test results and remaining life and maybe a money back guarantee offer?
Photo's should be in ad, showing general condition, markings, condition of pins and the embossed "Diamond" on the base, surrounded by the 9 pins.
Small signal genuine Telefunken tubes will have this embossed diamond. If not, it was built by another (NOS) producer and sold to Telefunken (rare but possible) or counterfeit.
Counterfeit is unlikely with the best tube sellers, these guys know the difference between tubes, some even read the manufacturer codes and include date and location of construction in the description.
I have almost zero problems with buying tubes like this, the only exception is VERY sensitive locations such as the first gain stage of a phono. This is an especially vulnerable spot as signal from this point on is magnified thousands of times by the time it reaches the speakers.
Be sure specifications are included in seller description such as test results and remaining life and maybe a money back guarantee offer?
Photo's should be in ad, showing general condition, markings, condition of pins and the embossed "Diamond" on the base, surrounded by the 9 pins.
Small signal genuine Telefunken tubes will have this embossed diamond. If not, it was built by another (NOS) producer and sold to Telefunken (rare but possible) or counterfeit.
Counterfeit is unlikely with the best tube sellers, these guys know the difference between tubes, some even read the manufacturer codes and include date and location of construction in the description.
I have almost zero problems with buying tubes like this, the only exception is VERY sensitive locations such as the first gain stage of a phono. This is an especially vulnerable spot as signal from this point on is magnified thousands of times by the time it reaches the speakers.