> From: wrt@eskimo.com (Bill Turner)
To: <amps@contesting.com>
> Date: Thu, 7 Aug 97 03:55:22 +0000
> 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!!
Great.
> 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?
That's the way they work Bill. I hope you have a fast electronic
overload system that samples grid current. You can trash the grid
pretty fast if the load even momentarily faults.
The 8877 won't take excessive grid current without damage to the
grid's soft gold plating, and it can even be accumulated damage done
over a period of time.
73, Tom
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