I've always been curious how this tube evolved. Can some explain the evolution of the 6550?
1) In the beginning, there was the black (solid)plate 6550 from Tung Sol, and it was good.
2) Then, Tung Sol changed to the gray solid plate, and it was still good (although some audiophiles will tell you it's not quite as good)
3) Following that, Tung Sol changed the plate structure to three holes. By this time, additional getters were added.
4) In the early 70's GE came up with the 6550A, which is supposed to handle more power (like a KT88) They were initially welded plate structure, and had some magic plate coating that is still a closely guarded secret. Sylvania also got into the mix, with their version of the 6550 (a very nice tube in it's own right).
5) GE changed from welded plates to stapled plates, and changed the plates slightly (a square hole in the center).
The question is, why did the Tung Sol evolve the way it did? Why did they change the plate coating? Why are the holes in the plates? And lastly, why did GE shift from welded to stapled plates? (I prefer the welded plate GE to the stapled plate, they seem a tad bit smoother, and very long lasting).
Lastly, why can't the Russians and Chinese make the current production 6550's sound and last like the old US types?
Wat do you reckon?
