The Maxi-Matcher simulates a real circuit and tests tubes in real-world conditions. We also check our tubes for other issues like shorts on calibrated and vintage tube testers. We match our tubes +/- 5% with an overall tolerance of 10%. While we do screen for noise and microphonics, even the best tube testers are quite bad at finding these faults.The only real test is with your ears. We guarantee that our tubes will be free of noise or microphonics but please be aware that there isn't a whole lot we can do to ensure your tube won't be. We guarantee our tubes for 90 days upon receipt. Noise and/or microphonic issues are covered. The item "New Ip & Gm Factory Matched Pair 2x Electro Harmonix 2A3 Gold Grid Vacuum Tubes" is in sale since Monday, November 12, 2018. This item is in the category "Musical Instruments & Gear\Guitars & Basses\Parts & Accessories\Amplifier Parts". The seller is "onlyglass" and is located in USA. This item can be shipped worldwide.