Use what you have if it puts out a reasonably good signal on AM. But if it's one of those rigs with "AM" mode that consists of one sideband plus carrier, that's not really AM; just SSB with poor carrier suppression, which doesn't demodulate well with a conventional AM detector, so it would be better to use something else. Fortunately, most of to-day's multi-mode transceivers transmit true DSB AM when in "AM" mode, but some modulate better than others. It doesn't matter whether it's tube or solid state, plate modulated or low-level modulation, leen-yar, etc. I have heard some solid state transceivers that transmitted AM well enough that I would have believed it if the op had told me he was running a modified broadcast transmitter. Some rigs are finicky to tune up and adjust on AM, so make sure you are doing it properly before trying to get on the air, or have someone help you get it adjusted right. Requesting help OTA is all right, as long as you don't impose on an ongoing QSO in the middle of some in-depth discussion. A dummy load can be very useful for tuning up, or practising tune-up procedure. If you plan to run AM with any regularity I would strongly suggest acquiring a monitor (oscillo)scope capable of displaying the envelope pattern. To me, transmitting without a monitor scope is like driving a car at night with the headlights turned off.