Catalyzes the S-adenosyl-L-methionine-dependent formation of N(1)-methyladenine at position 9 (m1A9) in tRNA. adenosine(9) in tRNA + S-adenosyl-L-methionine = H(+) + N(1)-methyladenosine(9) in tRNA + S-adenosyl-L-homocysteine Belongs to the class IV-like SAM-binding methyltransferase superfamily. TRM10 family.