Plain TeX knows about the following fonts. They are all \magstep0 so for
our 300 dots per inch device are in directory t_1500:

AMR10.PX	12856
AMR7.PX	 	8644
AMR5.PX	 	6288
AMMI10.PX	13612
AMMI7.PX	8776
AMMI5.PX	6508
AMSY10.PX	16752
AMSY7.PX	10856
AMSY5.PX	8116
AMEX10.PX	40764
AMBX10.PX	15076
AMBX7.PX	8988
AMBX5.PX	6548
AMTT10.PX	11668
AMSL10.PX	12948
AMTI10.PX	13924