I was with my realtor girlfriend today to list the home of an elderly woman, and while we were being shown around the home by her younger brother-in-law(78 yrs young), we went to the basement and while looking at the electrical panel, I noticed a few small signal tube boxes. There was one box labeled GE 12AX7. Well I opened the box (box lettering seemed to be early 60's) there was a new 12AX7 marked General Electric. RCA made a ton of tubes for GE, and at first glance it looked like a gray plate RCA. Then I really looked at it, and it was marked Made in GR Brittan!!! Yes, it was a medium plate Mullard 12AX7, and the serial number began with B which indicates it was made in the original Blackburn factory. The gentleman who was taking us around, said, hey, if you can use it it is yours, and if you see any others help yourself. So now, I am trying to scope out the basement, without looking obvious!! Now, I do not care about my girlfriends listing, who cares that this is a deal, and the real estate market is in the crapper. All I can think about is finding a stash of RCA blackplate 6L6's, Tung-Sol 6550's, Telefunkens, etc....... Anyway, no such luck, but I did have the mullard, and some small 7 pin tube. But after getting home, I tried it in V1 in my MK IV, and WOW!!! I was currently using the Mesa SPAX 12AX7 (newer EH version, not Chinese) in V1. Well, the sound became warmer, fuller, and best of all, my noise level dropped noticeably. That has been my only complaint with the MK IV, is the tube noise when running in high gain settings. Some noise is unavoidable, but in a previous attempt to drop the noise level as much as possible, I put a Mesa SPAX in V1, thinking this would quiet the amp, but wow, the SPAX is not even in the same league as the Mullard. Anyway, I had to pass this story on to others who may understand, since when I told my girlfriend about what the tube did for the amp, she replied.. Thats great honey, I'm glad your happy!!!!