A swing kit -used when the dead key of a radio has been lowered- will give brighter modulation into a linear amp.
This provides two functions. The lower dead key of the radio will create favorable modulation scale so as not to overdrive the input of the amp - while the swing mod (usually a capacitor and a resistor) allows the radio to reach its peak modulation while in a lower power mode. Not to be done unless a linear amp is to be used.
It doesn't harm the radio - as much as it more accurately matches the radio to the input of the amp. I wouldn't do it to a radio - unless I intended to use an amp. Using a swing kit on radio w/o a linear cn be done; but it will give up some average power in order to make louder, clearer modulation...
Two cents...
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What gear do I use?
BASE: Icom IC-718 & GAP Titan DX, Yaesu FT-8800R & Diamond X50A, Magnum OmegaForce S45 & IMAX 2000 w/Astatic D104/TUP9.
MOBILE: Galaxy DX99V & Wilson 1000 w/Astatic D104-M2, Yaesu FT-8800R & Diamond NR-770.
"...The 444 in San Jose CA; the Central Gold Coast..." | 
Swing Kits 
Linear Mode
