You haven't filled your location in, so I've no idea where in the world you might be!.
But in the USA the ARRL are the national Amateur Radio organisation, and in the UK the RSGB are. Both of these publish books on the subject, I would suggest those as a place to start.
However, AM hasn't been used much for a great many years, so I'm not sure how much AM stuff might be in modern issues.
There are two basic methods of AM modulation, one (the older one) uses a high power audio amplifier and a transformer to modulate the RF power amplifier. The other (more modern) one modulates the carrier at a low signal level - this is then amplified using linear power amplifier stages.
There have been various old designs where the output stage is modulated via the cathode of the output valve.