About ten years ago, when I transferred the oldest tapes in the United States as part of the Mullin-Palmer collection, my good friend Don Ososke pressured me to use a full-track head for the project. I had started transferring these full-track tapes with a Woelke NAB stereo (two 80 mil (2 mm) tracks) head and recording both channels. When I obtained a Nortronics full-track head, the difference was night-and-day. The full-track reproduction sounded fuller, smoother, and quieter. There were no tracking problems to speak of that would cause azimuth wander large enough to create a “flanging” or “phasing” effect of in-and-out high-frequency loss.
About 2004-2005, I had some full-track 7.5 in/s tapes to transfer that had been badly warped and found that there was enough azimuth wander that the tapes sounded better using one channel of an NAB stereo head. If I used the full track head, while the results were quieter, the azimuth phasing was unacceptable. At that point, I was using a Studer A810 for this type of transfer.
A few years after that, I was asked to recover audio from a 7.5 in/s full-track tape that was part of the Monterrey Jazz Festival. The client was very impressed at my efforts. I was able to use the full-track head, but one of the major differences was that this time it was on a Studer A80RC rather than a Studer A810 and the difference in tape guiding seems to have been the “magic” in that transfer.
The rule is use the most stable transport available and the widest head available to capture as much of the sound as possible without annoying azimuth-wander-based high-frequency combing/phasing effects.
If you use a head narrower than the full-track width, there may be objectionable low-frequency fringing that would need to be compensated.