Most ECC803 tubes are fakes or called ECC803 to imply they're constructed or sound like the Telefunken. The Telefunken ECC803S has a frame grid construction (the "S" = "Spanngitter" in German or "frame grid" in English) and is used to eliminate microphonics. It's one reason why the later JJ ECC803 tubes cost around twenty dollars and the real NOS Telefunken ECC803 tubes cost around a grand. There are a few sites on the web showing real vs. fake tubes. If you find a Telefunken ECC803S going through old amps and stuff, that new tele can be yours! GE or Sylvania JAN 5751 tubes can be a great 12AX7 replacement.