This is a set of 3 GT ECC83/12AX7 S-Select vacuum tubes. Only vacuum tubes that have passed strict noise and performance tests are given the GT name. These are very expensive vacuum tubes nowadays. These were kept as spare tubes for an amplifier. They are new and unused. I will also be listing them individually, so please be aware that I will remove this listing immediately if those sell. How about using them for vacuum tube replacements in guitar amplifiers, etc.?