It would be good to know where you are "fluxwise" with the machine. By that I mean playing back a test tape (or one with a know flux level on it*) so that you know the output of the recorder and thus what level you can run with any given tape.
Once you have that key piece of information you can line up the machine for optimum noise and response. Bit of a faff but you CAN use a computer and DAW to both generate the tones and read the levels coming out. You CAN use a digital multimeter but don't trust them past about 300Hz, even the so called "true rms" jobs!
You should also de-magnetize the heads, guides etc but de-gaussers are I think a bit rare and expensive these days? Maybe there is an old tech' around who could do it? A local studio/radio station might help.
However, if you have had the machine from new and have never buggered about with the calibration it is probably near enough but you will need a service manual to check the line up, might be in the user handbook but I bet you will have to buy the former.
We, son and I, have a Teac A3440 but once computers came on the scene it was just to much hissy hassle!
Dave.