Didn't mean to kill/jack the thread, mods can delete my posts if they are not appropriate. I guess all this class C talk bugged me enough to want to have that conversation, but I'm no amp builder, so maybe I am doing the math wrong or not taking something into account.
If someone knows how to calculate the duty cycle differently than I did, other than putting the input watts across the transistor's input impedance and looking at how much of the resulting waveform is high enough to turn on the transistor, please chime in and correct me.
SSB needs to be biased class AB, because with no bias, only the loud sounds that result in enough RF voltage to make the transistor conduct would get amplified, and if the RF going into the transistor from a whisper or quiet syllable was only reaching 1v peak at the transistor's base, that would result in a low duty cycle for those quiet sounds because only the very tip of the signal would be high enough to turn on the transistor. During those quiet sounds, the amp would surely be running in class C, but not during loud sounds. So, relay delay aside, a SSB radio on an AM only amp with no filtering would create lots of harmonics on weak sounds and little distortion on loud sounds.
In AM, there is a carrier, so the quiet sounds can be amplified normally because the transistor is already on due to the carrier.
In FM, there is full RF voltage present all the time, so just like AM with a dead key, the RF is enough to get the transistor close enough to class B to not worry about it.
I never put much thought into why people lower the deak key for use with amps, but I will try now. Again, correct me if I am wrong. Wouldn't doing so put the carrier closer to class C operation which allows the transistor to run cooler during quiet periods thus allowing it to be pushed harder during the loud periods providing more punch/swing (at the expense of distortion during the quiet sounds)? Thats what makes sense to me anyhow.
I just cannot imagine an an AM only push pull amp running in class C when it has a proper dead key. Maybe this class C talk comes from the fact everyone drops their dk and thats what ends up happening, idk....