Thats a loaded question Lee....a few of them actually.
Here are a few observations based on experience or from qualified
sources.
I have not seen any published IMD data on the graphite anode versions and
will leave that up to someone else. The Amperex version has slightly
higher gain and could be a problem in an amp that is on the threshold of
instability. There are no specs on the Chinese versions that I am aware
of.
I have however been told that the graphite tubes require careful control
of the air supply and should not be used without chimneys. The reasoning
is that when a graphite plate shows color it is releasing gas and slowly
poisioning the tube. Amps with very marginal cooling such as the old Amp
Supply's are particularly prone to this. The Heath SB220 has adequate
cooling for the metal plate tubes but requires TLC with graphite.....plus
a few minutes of air cool-down after use before powering off.
The Chinese tubes are a varying bunch as far as quality but I have had
good luck with Pride. Svetlana is working on one according to W6TC but I
dont know the release date. The Amperex tubes are excellent
quality....just remember to run them cool.
73....Carl KM1H
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