Bill,
fully agreed, head alignment hasn't got ot do with it. I am no expert either, but accorgin to my comprehension, the tape head's properties create a reality the feeding or receiving circuit has to deal with, no matter if it is SS or tube driven.
All,
A play head hands out a certain maximum signal amplitude, located somewhere between the one of a MM and MC phono cartridge, the following amp has to amplify that with sufficient S/N ratio.
A record head is an inductive load needing a certain amplitude to magnetize the tape, the feeding amp has to provide that.
Same for the erase head.
The mean thing with a tape recorder is that for recording as well as for playback, it needs EQ, just the EQ for record and play is not the exactly inverse one. EQ is located in the amp, not in the head.
But to record linearly, you must hassle out the EQ in iterative steps until finally you are happy with it, no way to calculate it, so i was informed. In fact, EQ must be matched to the head used, maybe not for the sample but for the head model and on final test, a finetuning adjustment ensures that the tape recorder runs linear with one single tape brand.
I was not willing to follow that procedure.