I believe the amplifier in the D-104 was to allow the mic to be used with radios with low impedance mic inputs, one mic fits all. The amp had a lot of gain. I think the CB'ers just cashed in on that fact which made the D-104 popular with them ... disable the ALC, crank the mic gain up, grab a beer and cigarette, and yelling from 10 feet across the room splatter up and down 5 channels ... loud and proud. I have several D-104's and the ones with amps have the amp bypassed, they are not required.
73, Gary
