HI Jay461,I am using a pair of Sylvania 6SN7W metal base along with the Sylvania 6F6G to stunning effect, yes the metal base 6SN7W are very rare,I have two pair of Tungsol black glass round plates ,one pair as new, never been plugged in yet... There is something going on between the Sylvanias that I like better, I need more time with comparing the Tungsols and the metal base Sylvanias.I am hunting down another pair of Sylvania metal base and will sell my near N.O.S. Tungsols once I find them.The tube store has some Philips mini watts non metal base for your p.s. if you are interseted.