Tubes for a pre stage... matched NEW or unmatched identical NOS?

i would always go for matched sets when they appear in serious hifi gear

of course testing does not guarantee the electrical match seen on the tester will persist over the lifetime of the tubes in use, but it is a much better starting point than starting with wildly mismatched ones at the get-go

that said, i agree with others who have said that old stock 12au7’s are still plentiful, and not very expensive

i have over a hundred of them in matched sets collected since the 80’s, mostly american made ones (sylvania, rca, ge and so on) ... happy to assist if anyone here (in the usa) needs some

from stereophile’s review of the sphinx v3

Description: Hybrid integrated amplifier with 12AU7 tubes in line stage and class-D output stage. Power output: 100Wpc into 8 ohms (20dBW), 200Wpc into 4 ohms (20dBW). THD: <0.1% typical, <1% at rated power. Frequency response: 5Hz–20kHz, ±1dB. Input sensitivity: 1.0V RMS. Power requirements: 115/230V–50/60Hz.

12au7 pair is in line stage, not phono stage (which is solid state)...

...not to say that matching and low noise are not important, but just significantly less so than if it were in the phono stage

people posting seem to be getting confused, referring to 6dj8 tube variants and such, when the op is specifically asking about 12au7 tubes and their equivalents

12au7’s in usa or european old stock form are plentiful and relatively inexpensive, even for well matched sets - no need to play with the relatively grim and unreliable chinese and russian current production when so many nice old stock ones are around

having said this, the 6dj8 types -- especially higher end dutch or uk cca ecc188 variants, what have you, that is a different universe, an entirely different discussion about value, availabilty and affordability

i agree that clear tops can be a little tizzy... regular top getter rca’s seem a touch smoother

as usual, tubes, like anything else in a good system, is subject to synergies (or lack thereof) and the taste of the listener