I just finished my ST120 Build. What a great experience and a great kit.
This amp sounds great. At first i thought it wasnt working it was so quiet. I mean its silent. Even after the few little changes i did. I ended up using stranded tefzel wire. I did ground the chasis, also I am not switching the neutral but rather the hot. Both work but it is safer this way. I also put an x/y line rated 0.01mfd cap across the switch. Figure it might save the contacts over the years. I replaced the chinese rectifier tube with a Sovtek. Noticed my bias went up, so i re biased. All in all a beautifull build. I tried my hand at the lost art of wire lacing with waxed lacing string. Turns out it takes a bit of practice. so is stoped. See attached. Also, used one of the unused connections on each of the front sockets to add a chasis ground test point. This was i avoid risking scratching the chasis with my meter leads when adjusting the bias.
I posted a bunch of photos at this link