Chinese A, B,Cs all sound good in the SLOs I had. Just like in a Marshall, they work well. I have a batch of A's at present and they are great. Amperex are great too but a little spendy.
I've tried many and end up back with the wafer bottoms 5881's biased at 30ma .
I think many dog the Sovtek 5881's because they come from the factory cold around 21ma .
Up the bias to 30ma which is around 65% max dissipation and you warm the tubes up and makes the amp sound fuller imho .
what ? 3 SLO100? you probably like them so much that with each different type tube that gain slightly different tone and feel huh ? am interested in the diff using kt66 as the tube looks typically huge... is the kt66 direct replacement of the 5881 ? how you set the mA and PV per tube for your kt66 ?
Honestly don't remember, Dave Friedman biased it for me and I just don't remember. That SLO has a Hiwatt preamp section, but I tried the Gold Lions in a stock one and dug them. Mike had built a custom one for me, then #19 came up for sale, so I have 3. But yes, they all sound a little different with different pre/power tube sets.