Sound is very subjective. I built it into a combo housing made from 18 mm solid wood, with a half open back. The speaker I used is a Jensen P10R speaker. The sound and control descriptions from the reviewers before me are absolutely correct! Very interactive tone and volume controls, nice compression like overdrive from the master volume.
The stock delivered 12AX7 is a nameless one, but looks exactly like a JJ 12AX7. The 6V6 is actually a russian 6n6p. With the stock tubes I got a really nice Fenderish sound! Great in combination with a strat or tele. You want vintage Fender tone, stick with these!
However I did some experimenting with other tubes. First I tried a TAD 6L6WGC-STR with the stock 12AX7, I found it to be rather harsh sounding compared to the 6V6, it did sound better when I used it with a 2x12G12H30 cab though.
Next I tried a Tungsol 5881 tube with a Tungsol 12AX7, this combination is the best one in my opinion! Excellent overdrive with the Volume and still a lot of headroom when cranking up the master volume, this also adds a very nice compression rather then overdrive to the sound, very rich sounding!
Finally I replaced the 12AX7 with a NOS 5751 to tame the preamp a bit. This trick works particularly well if you need a clean(er) sound at nearly full volume(s). Downside is that it removes the interactive magic when playing with your guitarvolume to break-up the amp into a nice overdrive.
I returned the tubes to the Tungsol 12AX7 and 5881 which I like best. However I want to try a KT-66 to see if the amp will become a bit more JTM-ish.
Geoff told me a friend of him swears by a 6551, which is like a KT-88. i might want to try that one as well.
Great platform for experimenting! My experiences with the tubes are with the P10R Jensen speaker, using other speakers may make a huge difference in the overall sound experience though! I get a lot of compliments about how excellent it sounds from my friends and band mates. This amp sounds particularly well with my Classic Player Strat and Am.Std Tele.
For use in a band however it's barely keeping up with the drummer, but add a mic in front of it and you have a great sounding backup amp on stage! During rehearsals it's good for rhytms but lead tones miss just that extra bit of bite. More efficient speakers may help a bit, but it's no rocket science that a 5 watt amp has some troubles keeping up with a full band. It accepts pedals very well, very nice with a TS808 and Wah in front of it.