I have had great results with Shakti stones. Not too heavy and as well as damping they deal with issues from transformers. The size suits your needs.
Btw have you also tried Herbies tube dampers? Check this thread for what to expect
https://forum.audiogon.com/discussions/tube-dampeners-on-arc-gear-free-tweak/post?postid=1367353#1367353
Btw have you also tried Herbies tube dampers? Check this thread for what to expect
https://forum.audiogon.com/discussions/tube-dampeners-on-arc-gear-free-tweak/post?postid=1367353#1367353