Atma-Sphere MA-1 amps

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.

I swap tubes around every few months - there are many great combinations. NOS tend to last much longer than contemporary brands - or so everyone says - I haven't had a 6SN7 go south on me yet, so no direct experience.

MA-1 Mk.III ---
Driver: Sylvania GTA or RCA GTB
Tubes 2&3: VT-231 Ken-Rads (these positions have biggest influence on sonics, imo), RCA Grey Glass
Tubes 1&4: VT-231 Sylvania, RCA Grey Glass, or VT-231 Raytheon

I really like the VT231 Ken-Rads in the the amps. They're still out there but getting a bit (more) pricey.

Couple notes:
i) My Mark IIIs are in the traditional narrow chassis, so position may be different w/ the newer style. Driver is understood as position #5 at the edge of the chassis facing the output tubes.
ii) For NOS, the driver position requires a GTA or GTB - something that supports a higher 450VDC plate voltage; the other positions do just fine with other NOS (eg. GT or VT231).

The preamp is both challenging and fun because of the phono section, where it is harder to get good *quiet* tubes - but its definitely doable.

MP-1 ---
forwardmost 6SN7: VT-231 Ken-Rad
other 6SN7: Electro-Harmonix or stock Chinese
phono (12AT7s): CV4024 Mullards, '60's Siemens 12AT7s, 6201 Sylvania Gold Brand

I put Herbies Tube Dampers on 3 of the 5 6SN7 per channel and 3 of 4 12AT7s per channel. The dampers work well.

check this out:
The Reference 6SN7 Thread

The gear is incredibly revealing of tube changes (for that matter any change) and tube rolling becomes lotsa fun. Good section matching w/in a tube is v. important.
 
Tim