The 3-500 is a very well designed tube. I have seen 1500 watts out of
a single tube for short SSB contacts on 50 mhz. (still in service) They
are fragile after the filaments have ran for a while so avoid any
excessive handling of old tubes. Going up the side of a mountain on a
motor cycle with a pair of 3-500 strapped to the back, will do them in.
They were in the upright verticle position at the time, so it probably
didnt matter. The anode will turn white after it goes cherry. The next
stage is you start to see the grid wires outline through the plate
material and tiny sparks start emitting from the material. At that point
the glass envelope will deflate allowing air inrush to the elements. Its
all over from there but what a rush. Once you have ever seen and smell
that happen, it changes you forever.
The carbon element versions are like the old 813's were, Tough! Never
run a cold tube, heat that baby up. If it blows you didnt want it
anyway. A good amp guy has got to know his limitations!
Ron W4WA
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