A message from the seller. Hello, These are mfg. in a new plant in China for Penta Labs. The quality control on these tubes is excellent. Penta ages these tubes for 24 hours and then RF test them before they are boxed. I have a pair in my Henry Classic X with 4000 volts on the plates and they work just as good as the Eimacs I took out. Frank K5SVC -- Randy Pence N4JZY