Here is what the L-1000 manual says. AM operation is basically the same for bias settings
as SSB. The issue is drive and loading. Careful reading of the pages I am attaching should do the trick.
One needs to load the linear amplifier to be used in AM operation for full power out with a carrier. The drive should be then reduced to approximately 1/6th the full carrier output. Note: some would say 1/4 but I disagree - I suggest 1/6th. This information was made available at
http://bama.edebris.com/manuals/b&w/l1000a/ But I think you already know that.
With the suggested carrier power level I suggest you should have plenty of head room for ~ 125% positive peaks. Be sure to properly phase the microphone input to properly phase the asymmetrical characteristics of the male human voice
GL, Al
