Re: KPA-500 "Output for Input" schedule?

Posted by Julian, G4ILO on May 11, 2011; 6:28pm
URL: http://elecraft.85.s1.nabble.com/KPA-500-Output-for-Input-schedule-tp6352735p6353030.html

Don Wilhelm-4 wrote

Of course it can be driven by lower power.  The KPA500 is a linear
amplifier.  If 40 watts in produces 500 out, then 20 in will give 250
out and 10 in will produce 125 watts.  If the relationship is otherwise,
then it is not acting as a linear amplifier.  The same thing should be
true for any linear amplifier - that is the definition of linear operation.

If it does that then it will be the first linear amplifier I have ever seen that actually keeps that relationship across the whole of its range.

Most solid state amplifiers exhibit noticeable compression as you increase the input power, so you get a lot more than half the rated power out for half the specified drive power.

Take a look at the figures for this Mirage amp (selected at random as being the first spec sheet I could find that proved the point.) It is only truly linear up to half its rated output. 10W in gives the rated 160W output, but 5W gives you 150W 2.5W would give you somewhere around 120W. The VHF amp I have here has a similar characteristic. Although it is designed to be driven with 5W input I am actually driving it with the K3/K144XV with less than half that power and still get virtually full output.

So I think the OP actually asked a very reasonable question.