I had a WA-6 years ago and was my daily driver until I updated to the Woo WA5-LE. One of the best upgrades to this amp was using an adapter to go from the 6DE7 tubes to 7n7 tubes (6DE7 to 6SN7 also work). 7n7 tubes differ from 6SN7 tubes in that have an loktal connector. Almost all 7n7s were made by Sylvania and are very similar to the chrome dome 6SN7, except they are quite a bit cheaper on the NOS market.