This is a capsule review of how eight different 6SN7 tubes sounded in my system. For you solid-staters, let this be a (perhaps frightening) glimpse into that curious medical condition known as "Toob Madness".
The 6SN7 is an octal tube used either in preamps or as a driver in a power amp. There is a body of opinion that considers the pinnacle of octal-based preamp design to be the MFA Luminescence B1C or Lumi for short. By an amazing coincidence, I happen to have an example of just such a preamp in my system where it does duty as a phono stage. Feeding it via Lukaschek special cable is a Benz LP cartridge mounted in a Versa 1.2 turntable featuring integrated air bearing arm and vacuum hold-down.
The line level output of the Lumi is connected to a Manley Wave preamp via NBS Omega 1 cable. The 6SN7's do their thing in the Lumi's linestage. The Lumi pots are set to maximum yielding an astonishing gain ratio of 72db. Bring on yer most anemic MC cartridge. This baby can handle it.
The rest of the system exemplifies the expensive amp, cheap speaker philosophy. The amps consist of two pairs of Manley 440's and one pair of Manley 500's. Yes, Toto, we're in the land of triamp. The speakers are two pairs of Eminent Technology 8A's bi-amped with the 440's and two pairs of Hsu TN-1220HO subs wired in series driven by the 500's.
Sylvania 6SN7GTB. The base of the tube is labeled in green letters. Big luscious sound. More relaxed than its highly touted siblings. More involving and transparent than the RCA which sounds a bit muddled by comparison.
RCA 6SN7GTB The circuitry in the Lumi is optimized around the RCA 5692 so it's no surprise that a tube from the same manufacturer would sound so good. Not as exciting as the Sylvanias, but also less tendency to sound etched. The choice between RCA's and Sylvanias will be highly system dependent.
Sylvania 6SN7W Distinctive nickel base. Quick and airy. Nice shimmer to cymbals. Lively. Too lively in fact. It grabs you by the lapels and after the initial excitement died down, I found it grating. I prefer its lowly stablemate; the 6SN7GTB variant that's more laid back presentation sounded more like real music.
Sylvania 6SN7WGT Very similar to the W variant above. Light, clear sound. Percussion has a nice attack.
GE 6SN7GTB. Big bold sound. Quite essy, otherwise great on vocals. Spoken voice very intelligible. Really unravels vocal lines on complex choral material. More syrupy than RCA's, with percussion not as good. e.g. metallic echo on steel drums.
Tung Sol 6SN7GTA Full tones. Tubby bass. Would work well in a system with an aggressive top end. Note this is NOT the legendary round plate Tung Sol that goes for upwards of $100 apiece.
Sovtek 6SN7GT. The Russkie offers a huge increase in dynamics vs. RCA 5692. Vocals acquire a new urgency and conviction where the 5692 sounds a bit sleepy. Downside: somewhat hissier.
RCA 5692. Legendary tube with the red base. Definitely softer, more rounded, duller. Less essy too.
The MFA Luminescence comes standard equipped with 5692's. The fact that they come in last in the sweepstakes does not in any way imply that the OEM is a knave and a scoundrel. (Obviously not, given the high cost of this tube.)
The 5692 is a militarized version of the 6SN7, originally designed to work with artillery (all the vibration was destroying tubes at a frightening rate). Scott Frankland (the F in MFA) has written that they chose the 5692 because of its longevity (10,000 hours!!!). All that ruggedization paid off. And they liked the sound. I happen to disagree with the latter assessment, but that's just my opinion. It took the Sovteks three years to go microphonic in my unit. In my book, that's an acceptable time between replacing tubes as is the replacement cost (my chosen Sylvania 6SN7GTB's cost around $40 each).
I have barely begun to scratch the surface of the vast number of 6SN7's available out there. In fact, I've barely begun to scratch the scratch. There are different manufacturers than the ones listed here. And within a given manufacturer's offerings there are a dizzying number of variants. Add to that the issue of the age of the tube. Like fine wine, tubes have their vintages. In the case of tubes, it's considerably simpler - a good rule of thumb is the older the better.
I would like to thank for Andy Bowman of Vintage Tube Services for supplying the tubes in this survey. You can pay more (or less), but you won't find a finer tube.