> Negative feedback has little to do with being better at
> reducing the
> distortion produced by running into grid current than
> having no feedback.
> Sure an amp with feedback is going to lower the overall
> distortion X number
> of Db but on a relative scale overshoot problems are going
> to create the
> same amount of difference in distortion products whether
> there is feedback
> or not.
A sharp transient is quickly gone and has little average
power. Until we clip it. The worse thing we can do is turn
that sharp transient into a long period of non-linerarity as
the grid voltage pumps way up and then recovers. Making the
already clipped waveform even flatter for a much longer time
doesn't help bandwidth either.
> The question still remains, how do you protect the grid of
> a 4CX type tube
> from excess grid current with a stiff bias supply?
We could just shut the amplifier off until the person fixes
the drive problem, and/or do fast attack ALC with a long
hold time. We don't need to turn the PA class C for multiple
RF cycles over and over again just so the operator can keep
on transmitting without popping the grid.
I had a few rigs that were terrible. One was an IC775DSP.
When set for 50-60 watts it would spike to around 350-300
watts. My AL1500, when loaded normally at 2000w carrier,
would just dump when I used it. If I had a loose goose grid
I'd never have known it was a problem.
A very fast grid trip circuit not only can save the tube....
it can let the operator know something is wrong.
73 Tom
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|