[AMPS] Tuning Up?

Sun, 17 Aug 1997 20:54:42 +0000

> 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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