safebelayer,

From your description sounds like the tubes went microphonic.

Thanks for the suggestions. I wasn't tapping the tubes hard at all. I'll try some 5933 tubes tomorrow.

I'm having a different experience with the 5933wa tubes. The tone is beautiful. The bass doesn't slam, but it's definitely present. One of the most realistic sound producing tubes I've tried. Here's a list of my past tubes:

EL34: Svetlana reissues 👎, nos SED winged c 👍, NOS Mullard xf2 👍

6L6 types: nos Svetlana winged c 👍👍, tung sol reissue ok, 6p3s good, 6p3s-e 👍+, tung sol 7581a 👍

807: RCA 👍  if not microphonic, Sylvania 5933wa 👍+

Kt77: gold lion reissue 👍

Kt66: gold lion reissue ok

6ca7: NOS Raytheon ok+

If anyone has questions on a specific tube type, please pm me. Too much to write here to give reviews on each.

I’m not surprised that those RCAs are microphonic. If they are the last gasp 1970s or 1980s production, no wonder. The RCA is have all those naked wires running from the plate down to the bottom of the tube whereas the other manufacturers put that metal girdle around the wires as they exit below the plate. I don’t know if that is more than aesthetics at work. I acquired a group of 1970s RCA 807 tubes And they tested extremely high for trans conductance, 6000 to put that in perspective the older national union and other tubes tested around 3800 to 4400. Mind you this is the 6L6 test data which calls for 5000 as a normal tube. So the high trans conductance explains the lively presentation