This adapter allows you to use a 6SN7 / 6SL7 tube in a 12AX7/12AU7/12AT7/ECC83/ECC82 socket that is wired for 6.3v heaters. All 6SN7 / 6SL7 adapters on ebay need to be plugged into a 6.3v socket. The adapter lets you replace a 12AX7 family tube with a 6SL7 or 6SN7 tube.