Quote:
Originally Posted by kx250rider
I know that since they haven't made 5U4Gs for half a century or more, they must be diminishing.
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Actually, they are still being made:
http://www.amazon.com/Sovtek-5U4G-Du.../dp/B0002M71S0
http://www.sweetwater.com/store/detail/MB5U4G
http://www.tubeman.com/item196.htm
Apparently, the audio fetishist market is large enough to justify producing these, even if they are inferior to the straight bulb types. Makes perfect sense, considering that you can also buy 6SN7s with Western Electric style "tennis ball" bulbs on them:
http://www.jacmusic.com/chinatubes/6SN7-Globe-400.JPG
So they take a crappy Chinese 6SN7, and make it even MORE microphonic by removing the structural support and damping provided by the mica supports against the inside of the bulb. And then charge a premium for them!
If you want the best of all worlds, remove the 5U4G bulb from the base, install a pair of 1N4007s inside the base, then epoxy the bulb back on. Solid state reliability, reduced heat load, and the correct vintage look.