To: <amps@contesting.com>
> Date: Sun, 17 Aug 97 21:06:17 +0000
> This question is likely too simple, but I'll ask
> anyway: What is the "fool-proof" way to tune an
> amplifier?
The best way depends on the type of amp.
Most amps are best tuned just slightly beyond the maximum output
power they can produce (loading control moved to slightly **less** C
than that producing max out) with FULL drive power, within the
ratings of the tube. Momentary overloads won't hurt the anode or
cathode, but they can cause damage to the grid. The damage can be
accumulated over time with gold plated grids, every time you
overdrive the grid--even for an instant-- you might be dislodging a
little more gold from the grid.
Your amp uses tubes that should NEVER be overdriven, and
they should always be protected by a fast acting overload
system...not a fuse.
By the time you might notice the grid current meter being too high,
the current very well might have eaten away at the grid a little bit.
To many of these "little bits" and the gold will poison the cathode
or contaminate other areas inside the tube. It isn't like a tungsten
grid that can be heated incandescent, cool, and keep on working.
> Upon increasing drive and going to operation, I
> noticed a lot of grid current.
Never tune a PA at low drive, and then increase drive without
re-tuning. Not only is it tough on the tubes, it's hard on tank
components (that is a major cause of arcing and damaged
components) and it makes the amp splatter.
That's why a fast acting grid overload circuit is so nice. It'll trip
off before the meter even moves, helping prevent splatter and
tube / tank damage.
> Can you help in providing a "fool-proof" solution
> to tuning (one that works in the middle of the night
> in the middle of a contest etc)?
Put a peak detecting grid current indicator in the amp, that knocks
the thing off line. Then you'll always be safe. That could be the
best twenty dollars worth of parts you ever bought, and a lot
cheaper than new tubes.
> I like to take the very best of care of my equipment
> and hate to see excessive grid current even momentarily
> (2x3cx800's).
The tubes hate it even more than you. ;-)
If you don't live in a perfect world and aren't always perfect, add
the circuit. The amp will be better able to take care of itself.
73 Tom
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