[Elecraft] How to use external ALC with the K3 (applies to the SPE Expert or any other amplifier)

[Wayne Burdick]

K3 external ALC setup is covered on page 27 of the owner's manual.  
Please read this page before attempting to use external ALC with any  
amplifier.

Executive summary:

1. DO NOT turn the K3's power all the way up and use amplifier ALC to  
maintain peak power at the output of your amplifier. This WILL NOT work.

2. Instead, adjust the power level at the K3 to provide just enough  
drive to hit the peak power desired at the amp. You may want to set  
CONFIG:PWR SET to PER BAND so you don't have to adjust power each time  
you change bands. (This is also covered on page 27.)

3. External ALC is accommodated as a safety backup in the event that  
peak power suddenly increases, etc., due to a failure or load change.  
When properly applied, it will rarely be needed.

Technical details:

The K3 is designed to *not* depend on fast external ALC, because that  
absolutely, positively causes splatter. We studied lab work from  
several authors on this topic and decided to take a different  
approach: our fast ALC is all applied *ahead* of the 1st I.F. crystal  
filter (it's handled by DSP, at the AF and 2nd I.F. stages). We do  
apply slow, long-term ALC after the crystal filter, but this can't  
cause splatter because of the long time constant. External ALC, if  
used, is factored into this part of the equation.

Yes, the K3 is unique in this regard. It may be slightly inconvenient,  
but it will result in a cleaner signal.

73,
Wayne
N6KR