If you can find them NOS GE solid grey plate 6550 tubes are my favorite 6550 type power tube. Another favorite also are NOS Sylvania 6550 tubes. I've used these tubes in a Jolida JD-502P amp at various times.
If you are going to go for KT-88 type power tubes my favorites are JJ Blue Glass KT88s and the Penta Labs solid plate KT88s. I believe Doug's Tubes on Long Island has the Penta Labs in stock.
If you are going to go for KT-88 type power tubes my favorites are JJ Blue Glass KT88s and the Penta Labs solid plate KT88s. I believe Doug's Tubes on Long Island has the Penta Labs in stock.