We both forgot an important reason to forgo phase modulated AM, way too many tubes which raises operating costs all in itself. The Continental 317-C uses far fewer so is economical, very popular and one more bit of reduced AC power requirement, screen grid modulated finals in the Doherty configuration. (If I remember right he was a ham cartoonist, hi.) Eh, if you're power mad why stop there, you might find a 105-C around someplace. Ah, that's a puny megawatt, if you want to add 3dB to that there's a band switching shortwave Collins in Greenville, NC...............
"I wouldn't mind getting hold of a 500 W or 1 Kw Bcast AM transmitter..."
That 200A 230V single phase main would yawn and go back to sleep, typically the mains breaker for a KW broadcast transmitter is 40A. I installed a few, ran the wiring and put the cutoff switches on the wall next to them, when stations went solid state we saved SO many tubers from the scrapper.
Since I've already posted 1KW broadcast transmitters too many times here's your Continental at the WNEW plant. Not exactly underwater there's still a bit of wreckage across from WMCA on Patterson Plank Road, not the Jersey Shore, the Meadowlands. What's here at the Jersey Shore are relics, the defunct AT&T transatlantic HF station WOO in Ocean Gate and the old RCA maritime CW station in West Creek, ex WSC now W2WSC, the Tuckerton Wireless ARC club station. Since I don't have a photo of WOO here's something else of interest besides my AT&T avatar.
OH, ALMOST FORGOT! One of the local clubs (Tesla?) made an agreement with AT&T to lease space at the site, turn it into a museum and use the old antennas. That would give the boys down in West Creek a run for the money but last I heard Sandy did extensive damage putting it all in doubt. I wish I had a better connection to the jungle telegraph, it would be nice to know what's going on in my back yard.