5963, 5814 and 6189 tubes are military/industrial versions of a 12AU7. They were made primarily for the US military but were also used in industrial test gear in the 1960's and 1970's. They were made primarily by GE, RCA and Sylvania and (IMHO) are better than most currently made 12AU7 driver tubes .. I have a good stock of these tubes and ship them as driver tubes for all customers that want a tube set with their VTA amp kit. If you go out there and look for these on Ebay or other web sites that sell tubes, the 5963 versions tend to be a little less costly than 5814 or 6189 versions but I find no real advantage of one over the other. IMHO all three are of equal quality and getting 5000+ hours out of these is fairly normal. Yep .. Every now and then you might get a noisy or microphonic piece but as a class, these tend to be less noisy/microphonic than other types of tubes like the 6DJ8/6922 type tubes. The British military version of this tube is the Mullard CV4003. The Mullard CV4003 tubes, however, are getting very pricey .. If you can find a CV4003 under $50, you are doing good.