Tv7 tested TUBES. NOS is subject to interpretation and there is no specific definition for it either. There are suggestions and opinions. 90 % of our tubes are Tv7 tested. Tube testers do not test for these problems in the manner in which you think, except to the extent that a tube tester with sensitive leakage detection will find far more “noisy” tubes than a tube tester with only “fair” leakage sensitivity, to the extent that the noise is due to this problem.