I have a couple 12au7 type preamps. For nice clarity & sound or a step above the usual suspects of 12au7’s I think the Siemans with silver plates are a great tube. I also always seem to like anything Holland Amperex. I find that the much cheaper early GE tubes to be close in sound to the balanced characteristics of Amperex tubes. Valvo’s are always a winner as well.
If your transformer can handle it I really prefer the E80cc tube. They have a 10,000 hour life span so you definitely get your money’s worth. Great clarity & dynamics. The Tungsram are a fine tube. I recently bought some PCB’s from Mellow Tone Kits & just copied their e80cc schematic & it was a good preamp with lots of drive & low output impedance I paired with a Hypex Nilai.
I’ve also tried the e80cc with adapters in my 12sn7 & 6sn7 preamp circuits. I preferred them with 12v on the heater but will work with 6.
The American 5814 tubes are good 12au7 types as well for the money I feel. 12bh7’s even better if the transformer will allow.
For 6sn7’s the early 50’s Sylvania chrome dome gta’s are a safe bet. Some pretty good 6sn7’s that don’t have a crazy price tag are the early 50’s GE GTA’s. Side getter, copper grid posts, parallel gray plates, short bottle. I just picked up another nice pair recently for about $50. GE’s don’t get much love as any tube type..but they have some gems that can be found cheap due to this No Love. They are great as cathode followers. A lot of the VT-231 type tubes are just stupid expensive in my opinion. I don’t notice a big enough difference in good 6sn7 tubes to justify the cost.
I am a fan of the 5692 tubes when plate voltages are under 200volts. These are expensive but in the right circuit are very quiet, transparent, dynamic, enlarged soundstage, just smooth & sweet. 10,000 hour life to maybe justify some costs. In the wrong circuit (high voltage) they can sound grainy & lifeless..& burn out quick. I also like most early RCA 6sn7 types in general. Smoked glass being less transparent but fun for certain genres.
6cg7 types with 8 to 9 pin adapter go nicely in any 6sn7 spot. These are identical to 6sn7’s in 9 pin form.
I prefer 12volt 12sn7’s..though they are supposedly identical to their 6 volt brother/sister.
I’m currently using a pair of Sylvania JAN CHS 6sn7wgt in my Icon Audio LA4 preamp & liking it. I’ve used other wgt’s in the past & didn’t totally love them. This pair that I really like actually took me awhile to put together a matching pair..buying one & finding a match many months later. Compared to my other wgt’s these have the bottom round plate slightly above the base, a half chrome top but can see the 4 hanging filaments. Mid 50’s, 3 hole, shorter bottle but without super short plates..white lettering.
Buying singles can lessen the cost but can sometimes take awhile finding a good balanced match.
But I think it really comes down to the circuit if the tubes sound well. And almost all tubes should sound good to decent in the circuit. Usually if NOS tubes don’t sound good it’s probably because something is wrong with one of the tubes. If the tubes are good the music should sound good..some tubes just sound slightly better than others. Everything in this post is just my opinion of course.
With quality tubes being so scarce & ultra expensive I should really start trying more aftermarket/new tubes to see what works well. I have no experience with newer tubes.
