Hi, My understanding was that standard tube conventions had the leading digit(s) as the filament voltage: 1B3 = 1 V 2X2 = 2 V 5Y3 = 5 V 6X5 = 6 V 12AX7 = 12 V 35W4 = 35 V 50C5 = 50 V 117L7 = 117 V etc. How does a 2C51W dual triode fit in? It has a 6 V filament? -John ===================== ===============