A few days ago I received a Willsenton R8 and I’ve been playing with it drive  a pair of circa 1992 Nelson Reed 804C speakers (an efficient front ported 3 way design using Volt woofers,  ATC midrange drivers, and Scanspeak tweeters).  I ordered the R8 with the stock ”Willsenton” tubes  instead of premium tubes because I have a pretty good collection of spare tubes so I didn’t see any point of splashing out more cash  for tube upgrades. The first thing that I did was listen for a couple hours with the stock tubes.  I was reasonably impressed at how big of a sound it was producing but it occurred to me that it was making my Nelson Reeds sound like Cerwin Vegas – dynamic but lacking in subtlety; sort of hard sounding with a tendency toward producing one-note bass. Next I opened up  the amp to verify that the internals matched those of the MKII version of the amp shown in your YouTube video. It does. Three days into tube rolling, what I’ve settled on as the best sound so far is using “triode” mode with Tungsol KT120 for power tubes, Linlai E-6SN7 tubes in the phase splitter slots, and Philips JAN 6188 tubes in the 6SL7 slots.  I left the Willsenton 6SN7 in place in the preamp (center) 6SN7 slot because I only had two Linlais. Now I like the sound - the hardness is gone  and the problems  with the bass are less pronounced and the amp sounds big even though with  KT120s in triode mode the amp  probably only puts out about 20 watts  per channel.  However  I’m a little concerned about using the KT120s.  I think that I have a good quad of them (there were part of a matched octet that I bought from Kevin Deal in 2019 and then didn’t use very much) but it’s conspicuous that Willsenton doesn’t list them as a compatible replacement. Do you think that long-term use of KT120s  in those amps poses  a reliability risk?