I have a 23 yr old Peavey 2X12 VTX Classic,with 6L6 GC Sylvania tubes. Does anybody know what the best replacement tubes are for this Amp? Groove Tubes? Ruby tubes? 6L6 Gc's? 6L6 GE's? 6L6 R's? 6L6 S's? Or is there any other Family of tube I can use in their place? Thank you for any input.