Be careful when you chase these guys. The reputation of Siemens & Amperexes precedes them and they are frequent targets for counterfeiters. How do you know if a tube in question is the genuine article? Well, fortunately there are a few basic checks you can perform to differentiate true Siemens & Amperexes from relabeled Sylvanias and Tungsrams.
First, check the top of the tube in question. Siemens & Amperexes always have small ridges in the surface of the glass on top of the tube radiating outward from the nipple. These tubes will have 4 ridges, though sometimes only two of them are easily visible. The concept here is to look down on the top of the tube. The 2 or 4 ridges should divide the circular silver top of the tube in half or into quarters. No ridges? No genuine article pass on it.
Second, check the metal shield above the upper mica spacer. On Siemens & Amperexes it’s circular with two raised rectangular sections on opposite edges of the shield. On most fakes that shield is a perfectly flat disc.
Third, about 90% of Siemens tubes have a 1 or 2 digit number molded into the inside bottom of the tube glass centered between the pins. It can sometimes be very hard to see but it’s usually there. Remember, not all Siemens have it, but if your tube passes test one & two and has the number(s), it's a Siemens.
Fourth, familiarize yourself with the shape of the glass bottle on your stock Sovteks. Note that the top is smooth (no ridges) and rather rounded and the tube is short & large in diameter these traits are common to all Russian tubes in this family. Siemens & Amperexes are only about 80 to 85% of the diameter of the Russian versions and tend to have squarer shoulders on top rather than the rounded top of the Sovtek. You should be able to spot the difference between a Russian and a genuine NOS tube just by the shape & diameter of the glass pretty easily. One warning though Sovteks often (always?) have a number molded into the bottom of the tube between the pins like a Siemens, so know all the checks and don’t depend on just one to verify the tubes origins.
Fifth, if it’s a Siemens or Amperex 6922 or 7308 it will always have gold pins. So will some cheap counterfeits, so gold is no guarantee. But if they aren’t gold its not a Siemens or Amperex, so pass on it.
