I got them a few days ago but only had the time to try them today. First, I measured the plate voltage with the stock 5881s and got 420v. Then I measured it again with the 7581A set and the plate voltage is now 463v with the tubes biased at 37mA per the spec sheet that came with them. So they were right about that part.
But how does it sound? Holy shit, it's a major improvement!! The headroom is much bigger and the amp has considerably more volume. I was using the amp at around 4 to get stage volume before, now I can barely go past 3 before it's too loud.
Tone wise, the 7581As have slightly less midrange and a tighter low end, which I assume comes from the extra headroom.
So anyway, highly recommend these tubes for the SLO30!!!
