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Single Ended Triodes (SETs), the ultimate tube lovers dream.

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RE: SET for Home Theatre

Posted by tube wrangler on February 7, 2017 at 20:02:54:
A good 2A3 tube is an oddball. While a good 45 can give you lovely voices, some real bottom end, and can out-detail your pet kitten, a good 300B-- even the best (EML) just doesn't tell the tale like a 45.

The 300B that people "love" is simply drawing too much plate current. That means the output transformer has to get physically larger. TOO MUCH larger for ideal S.E. operation-- it kind of falls-off of the normality (for reproducing a real sense of presence-- at a live event) chart. (fictitious to be sure, but plenty real if you LISTEN to it...). Whoops! There goes a lot of your bandwidth, jump-factor and easy-to-drive capability. So much so that it begins to sound euphonic, not truly real.

BUT! The lowly 2A3 can really do it all and have more power than the 45.
2A3 tubes, of course, come in many kinds. There are the NOS BiPlates-- which always lose tons of coherent musical information, but can sound "fat"-- even pseudo-impressive.. But alas! It Ain't Real, Dude!

Then, you can try to round-up a pair of old RCA Single-Plates. These are
fairly rare, and good ones usually fetch about $1000.00 for a pair. Good?
Not really-- they're just too old-- the materials suck, compared to today's thicker glass, higher vacuums, and far better metallurgy. They ARE, however, musically coherent. You get that because of a geometrically-correct filament structure and a Single Plate.

Enter the modern EML mesh-plate and the JJ 2A3-40. The EML mesh is a
geometrically correct filament structure with a plate system that combines
pieces of both solid-plate and mesh-plate constructions into one plate structure. Best of both worlds? I have them, but prefer the solid-plate version, or the old AVVT Pure Woven Mesh. Just sounds more real to me....

The JJ 2A3-40 is something that people think is a 300B. It is NOT-- but it does use the plate assembly and glass bulb from their 300B. And why not? Works just fine. The rest of it is pure 2A3-- the filament and the grid structure. BOTH make the tube FAR superior to any 300B-- a fact that JJ admits to on their own website.

The 2A3 accidentally (?) happens to fall into "ideal" plate-current territory for a near-perfect S.E. output transformer. Not too big, not too small. And just the right amount of inductance. Cool! That area is 40-to-50 ma. The 2A3 tube LIKES that....., and it LIKES the usual 2.5K loading, although with the lower plate currents, one could go up to 4K or so-- that would amount to listener's preference and little else... measured distortions drop with easier loading, but so does low-volume dynamics. So which REALLY has the lowest LISTENING distortions? Nobody
measures THAT, I'm afraid...

Other advantages include easier-to-drive grid, and a 2.5 volt filament
which encourages balanced A.C. operation of the DHT filament-- this gives you a complete musical picture (with an unavoidable small amount of hum), rather than a partially rectified-out smothered, sanitized "cleaned-up" false picture of musical input... that operating Direct-Heated filaments on D.C. produces. This does not imply that Indirectly-heated tubes shouldn't use D.C. heating-- that works perfectly, but the 2A3 is a DHT.

There are 4 volt (filament) tubes that are DHT, and people also like those. There are even some 2 volt models out there in NewOldStock.

Why bother? The newer JJ 2A3-40 is such a screaming sonic and reliability bargain that it shouldn't be ignored....

-Dennis-