[Amps] 4CX1500 class AB1 vs. AB2

[Tom W8JI]

>> Contrary to the ham folklore, edging over the border into 
>> AB2 doesn't
>> have to be an IMD disaster. The two possible causes of 
>> IMD when crossing
>> from AB1 into AB2 are a sudden change load impedance on 
>> the exciter, and
>> a sudden change in DC grid bias. The change in load 
>> impedance is
>> minimized in modern amps that use a grid swamping 
>> resistor, and a well
>> regulated bias supply will keep the voltage constant.
Ian GM3SEK
>
> A regulated bias supply with AB1 operation?? That sounds 
> like a recipe for
> disaster.
> Gary  K4FMX

Why would that be a disaster Gary? It is a disaster when 
people have a loose grid supply and use them in what they 
think is AB1. Virtually every exciter on market today has 
severe overshoot at leading edges. If the amplifier changes 
grid supply change voltage during that transient it's a 
disaster for anyone else on a nearby frequency.

73 Tom