Another late bump here sorry. I just put a set of Tung-Sol "reissue" 7581A into Rogue ST-100 and am blown away at how full, vivid, and "classic tubey" the midrange is. A little less bass impact versus KT120, but still enough to nicely round out the sound. Rogue amps tend to have a clean, neutral & less tubey midrange (tending to dry at times) - switching to KT88 Gold Lion helps a bit here, switching into triode mode helps very little, and both of those are BLOWN AWAY by the juicy midrange effect of 7581A. Love it!!
I’m sure it’s a phenomenon caused by healthy amounts of low-order distortion, but I don’t care (good to counteract the sterilizing effect of most recording chains). It’s like getting the best of classic vintage 6L6 tube amps, but with better bass and more power. Rogue's ST100 is an ideal platform for tube rolling - individual tube bias adjustments, huge bias range, and only a quad to do.
The use of "reissue" on this tube is a a bit of a misnomer because Tung-Sol never made this tube. Its big maker was GE, and New Sensor has to roll up into their American label "Tung-Sol" because they can’t use the GE name ;)