Just fired up my new homebrew 8877 amp tonight after nearly two years
in the works. And it works! I can drive it to 1500 watts output
easily with about 70 watts from the TS-850S. It just sits there and
cranks out the power. Nice!!
My question is about the grid current vs loading. This is a
conventional GG circuit, PI-output with designed Q of 12, 3000 volts
on the plate, nothing fancy. Unlike my previous amps (3-500Z,
3CX1200A7) the loading control has a major effect on the grid current.
Once everything is properly tuned for max output, when I adjust the
loading control a small amount, the grid current varies a lot. I can
swing it from about 10 ma to 80 ma without appreciable effect on
either the input power or output power. It's weird to see the grid
current all over the map and yet the input power is constant. Is this
normal for an 8877? For a high gain tube like this, maybe it is.
Any comments?
73, Bill W7TI
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