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6AS7G tube types explained...

The 6080 is identical in performance to the 6AS7G. The 6AS7G is a ST/"Coke Bottle" glass type, whereas the 6080 is straight bottle. I almost universally prefer the 6AS7G. I have about 100 6AS7G/6080/6520/5998 tubes.

And it is the 6520, not the 6528, that is equivalent to the 6AS7G. The 6520 was only made by Tung-sol.

Of the US Makers, RCA-branded 6AS7G’s are by far the most common, and they sound good. Tung-Sol also made 6AS7’s, and they are a little better sounding IMO than the RCA’s (they are also constructed a little differently), but they are much harder to find, and not worth paying an enormous premium for. GE, Sylvania, Chatham and Raytheon also made 6AS7G’s, but they also don’t seem to offer anything the RCA’s don’t sonically, IMO. There are other brands available, but I am pretty sure they are just branded versions of the other manufacturers listed. The JAN (Joint Army Navy) versions were supposedly somehow selected specially (tighter tolerances, etc), but there are no construction differences with the non-military versions. I have seen JAN-6AS7G’s from RCA, GE, Tung-sol, and Chatham (which at one point was bought by Tung-Sol).

The GEC UK-made 6AS7G (A1834) are my favorite of the 6AS7G - they have brown bases and a different plate structure than the US types.

Finally, there are the Russian equivalent 6N13S, but I really don’t care for these. I have seen Amperex 6AS7G’s that say "made in Holland", and Ultron "made in W. Germany", but both of these were almost certainly Russian.

The primary construction differences in a 6AS7G are that some are made with a top halo getter (and the resulting chrome top flashing appearance) and some with bottom-mounted D getters (where the flashing is at the base and the tube has a “clear top” appearance). RCA also made “Grey Plate” and “Black Plate” versions – all other makers 6AS7G’s have black plates. Supposedly the Black plates sound better, but I believe this is either untrue or extremely subtle at best. Some also have an additional metal “skirting” shielding the wiring as it travels from the base to the grid, but I have not been able to attribute any real sonic differences there either. Bottom line – any Western 6AS7G is a good choice, as long as it’s in good shape and isn’t horribly microphonic.

There is also the 5998 tube, made only by Tung-Sol regardless of branding, which does have different operating characteristics, and may or may not work in any given 6AS7G application, although it does in the amps I have, snd sounds a little better than most 6AS7G's. In general the 5998 offers slightly more neutral sound, slightly better transparency, and are less likely to be noisy. They are approximately 2-3x the price, generally, and I have seen some idiots paying $50 per tube on Ebay when you can buy them NOS from reputable online tube-sellers for $25 each. Still, this is more than double the 6AS7G price.

The 2399 is also a Tung-Sol only tube, and I have never scored one myself, but supposedly it is also just a high-quality 6AS7G.

In general, the 6AS7G is a great sounding tube, IMO. I probably know more about this tube than any other tube type, as I have 4 different headphone amps that use it, and there isn't a lot written about it like there is with tubes like the 12AX7 or 6SN7...

Rob

"Let there be songs, to fill the air"



Edits: 06/06/09

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