Hi All I buy a little homemade head and dude keeps his Tubes and sends a list of Favorite tubes. Yeah these Muthers are pricey with a NOS Tun Sol Rectifier being the Cheapest. Anyway I finalle settle on the GEC 6V6's at power, and the 3 Pre amp tubes ar an interesting sort of bishes Valve 3 Black Plate RCA NOS Valve 2 12AX7 Valve 1 12Ax7 Notes V1 If less Gain is desired use 12AY7. V1 If more Gain is desired us 5751 (The 5751 is a Substitute for the 12AX7, but has Higher Gain) With a Trio of Tung Sol 12ax7's and the GECs good frikin grief waaay too much Gain. I sub in the 12AY7 and the gain has dramatically dropped off. This points the finger at the Power Tubes. Out Go the Gecs and in go EH 6V6. Gain is still a a bit anemic with the 12AX7 so I order a JJ off Amazon $19.95 (NOS RCAs are $40 a pop on these) With the 5751 in place I get a beautiful sweeping Gain, and I have ordered a Tung Sol 5751 for $32 to see where this goes. If I like then I will chase down a NOS 5751 which NOS are selling between $42 & $50 per Tube. Have you tried the 5751 in your 800 or earlier Marshall? If so I would love to hear your thoughts on this.