IMHO GEC 6AS7G is THE tube for the Crack, beats the TS 5998 in clarity (but for T90's which are a bit bright TS 5998 is perfect match).
I'd say just the opposite. As compared to ordinary 6as7(g)s and 6080s, the 5998, 7236 and 7802 have higher gain and higher transconductance, the latter of which lowers an OTL headamp's output impedance. As one would expect, this tends to make the sound a little brighter, faster and bass a little tighter. Ordinary 6as7g's and 6080's, including the much hyped GECs, raise output impedance and are a little be more mellow on the top end and a little fatter at the bottom end due to minor bass bloom. As described in an article on Pete Millet's site (http://www.pmillett.com/Wheatfield/rolling.pdf , see bottom of page 2), "The 5998, 7236, and 6528 have different characteristics than the 6AS7 and 6080 tubes, which lower the output impedance of the HA-2. The resulting sound tends to be brighter and faster than the stock 6080. Conversely, a good old-stock 6AS7G tube can fatten the bass and give an even more "tubey" sound."
I've made similar comments in the 650 thread from time to time and think they bear repeating here. The GEC, which I do own (purchased back when they were still relatively cheap), is simply a very nice, refined 6as7g equivalent. It looks cool, but honestly, I have a couple of $10 mil spec 6080's that arguably sound just as good. The hype surrounding this tube has reached the point of absurdity. Even skylab, who was head-fi's original proponent of the GEC tubes, has urged other head-fiers not to buy them at their present inflated prices - unless of course, you are buying for the sake of collecting, and not because you expect $200+ worth of improvement to your sound quality. The only poster who has repeatedly made statements to the contrary (no one in this thread) recently admitted having purchased a number of the GEC tubes on the cheap and then, after prolifically posting about them as the be all end all, selling them on head-fi at current ebay prices. The mods ultimately put a stop to it, but anyone considering buying a GEC tube should know the full story and approach that decision with due caution.
