I think that we are mixing apples and oranges here or are at least attempting 2 different discussions. Please allow me to clarify: The 6U8's (didn't seem to matter what brand) developed a hum over time. As posted earlier in the thread, several knowledgeable members suggested that the dc voltage on the heaters needed to be raised to prevent the 6U8A deterioration over time, which I did. The fact that the NOS JAN's hummed immediately and were microphonic was strictly due to the amp not liking them. (some time ago, I had some GE's do the same thing) I believe that some time ago when I searched AK for 6U8's that people liked in this amp, JAN's were not recommended, RCA's got a few kudos, so I have stuck with them and like them. I ordered the JAN's before I started this thread to see if they would last longer but I found out as mentioned earlier that it was recommended that the heater circuit be modified, regardless of the brand of tube used. Basically, I threw the JAN's in there as a test in case something went wrong after I modified the circuit (and used a dim bulb tester, of course!) As I said, when I installed the NOS RCA's the amp performs wonderfully, I am confident that the hum that used to appear over time will not re-appear. Hope that I have answered your question.