Atma-Sphere MA-1 amps

A question for NOS tube users - Howoftendoyou change 6SN7s? I have a set coming this week. I'm just wondering if I'm starting a very expensive and unsustainable habit.

Which 6SN7's do you guys use?

I mix RCA GTA Grey glass with Sylvania GTBs. Some argue that mixing is a good approach.

I use Sylvania GTBs with matched pairs in the two postions A-S recommend matching. The straight Sylvania lineup is a good match to my Aesthetix preamp. With a different preamp, some other mix might be better. The Sylvanias were a nice improvement in resolution, openness and timbre to the JAN Philips that I had once upon a time. Life expectancy on these is in multiple years of heavy service.
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In the preamp I use matched RCA GTs which are a bit more romantic than the Sylvanias. The GTs are generally not used in the amplifier because they can't handle as much voltage as the later GTA/Bs. RCA or Sylvanias are proably the most used NOS tubes by Atma-sphere owners as they are relatively available, affordable, and sound good.