Lightly used, matched pair of VINTAGE phonograde Mullard ECC83 / 12AX7 tubes sourced from Vintage Tube Services. These tubes are low noise, "green tip" selected tubes (green tip=phono grade at Vintage Tube Services) with exact matching date codes of I61 over B3B4; this indicates Blackburn, U.K. factory manufacture, in Feb. 1963. The tubes in this listing are the highly desirable I61 version Mullard 12AX7 made only from mid 1959 to 1963. The I61s have copper gridposts for tremendous midrange detail. On my calibrated Hickock transconductance tester, these 12AX7s tested at 88/90 and 87/89; for 12AX7s a result of anything over 65/65 indicates a good tube and most NOS 12AX7s test between 92/92 and 97/97, so this pair of Fleetwood/Mullard I61 tubes have at least 90% of their lifespan left. These tubes have completely intact printing, and "Gt. Britain" is etched right into the glass of each tube, leaving no doubt about their authenticity.As a final Mullard pedigree, these have the "pewter gray" top getter flashing that is thick and full. I ship USPS Priority, and I prefer Paypal, with no extra charge. Personal checks OK but must clear.