@@cobar5342 Thanks, we don't have a tube collection, only the store inventory. We once were roasted by someone online for hording precious tubes. But nothing could be further from the truth, we sell everything we have available. However as inventories of quality vintage tubes head to zero, Charles has suggested we start reserving examples of some of the rarer types, the Sylvania 12SN7 "Bad Boys" for one - probably the best sounding preamp tube ever made - unfortunately not as robust as the later higher spec'd 6SN7GTA.

Good choice !...............this tube does even not have a barrier cathode issue ...performance will stay for decades wheb used correctly ........sound may even get better over time . With the stock version sounds marvelous , that's the right starting point to upgrade components, wiring, connectors and volume pot ...etc . Only a very good design will benefit from this , not a design with flaws to try to hide the flaws ... I even do not use RCA connectors .....straight out and in with Neotech 1220 OCC AG wiring , no selector switch or whatever , only a Duelund tinned copperfoil on the output , Preheating and post heating of the filaments ........RGN1064 mesh rectifiers . Shinkoh 2 watt resistors and A/B......Black Gate capacitors....and Lunfdagl chokes. Sockets mounted on rubber suspension and point to point wiring. Rhodium IEC inlet and switchable bypass for the fuse ( at your own risk ) Do not forget to bias the heater voltage above the ground potential; No plastic isolation on te caps , .........copper foil to replace the plastic foil. BG needs long hours before revealing their magic , unequaled by any other brand , voices come out totaly free out of space of the recording .......layers of instrumentsfloat in gthe air beside, higher or lower, closer or further away..all will have body and air arround them and be separated one from another.....microdynamics will appear and shine without false upfront presentation........you can not buy a preamp with the same musicality in commercial totaly overpriced preamps ! Good luck and happy building . PS : Quality silver RCA plugs /Quality solder (AN or WBT )....lining the inside of the chassis with CU foil/quality noval socket ( military nos - AG)......shield cable for heater wiring. ../ better volume pot than the usual Alps ...Etc ... You will be rewarde with a totaly and silent black background.for the music .......no noise even better than SS ...........and a dramaticaly expansion of the dynamics from micro to macro level.

@@frankgeeraerts6243 Yes , this one rewards a bit of attention to detail. I was almost startled about the dynamics in this one, I perceived some extra punch via this one for sure. I did not go with raised voltage on heaters, but I went with filtered and regulated DC for the heaters. I use that voltage also for nice quality Japanese relays for input switching. I need 4 inputs you see. I went with RCA sockets, of the KLE type, which is basically same style as WBT. I also have full shielding of the circuit beneath my 2mm copper base-plate and I have both steel and copper in the transformer and choke housing. Also mounted a stepped attenuator built on Seiden swith and Takman carbon film resistors. All inn all very happy with it, thus I ordered a set of spare tube, they also sounds wonderful in my Crack HPA.

@@RaviNewfarm Nice .........thank you for reply . I also heard some good things about the Crack ! KLE is great ! ( use them also ) Tackman carbon sounds very good without ruiniing the budget .....

@@ahmadathari3503 no the 6CG7 is a completely different tube (medium gain) compared to the high gain 12ax7. The only acceptable tubes to sub for the 12ax7 are the slightly lower gain 12at7 or the higher spec'd 7025.

@@tubelab194 thank for your answer, what ablout 12sl/sn7 instead of 12ax7 with converter socket?

@@ahmadathari3503 again it's a very different tube. And adapting from a larger octal tube down to a miniature 9pin is not practical. Going the other way, mini 9 pin to octal is fine structurally. The 12ax7 is a unique tube and should be replaced with 12ax7's. We should still have stock of some excellent vintage 12ax7's. Note if you sub a different tube in a phono preamp the EQ will be changed.