You guys are right of course. I guess I'm just hoping to stir up a little brainstorming and see what kinds of ideas other members have daydreamed about.
I have a couple of ideas about ways to move the tape a little more precisely. They may well have been tried at one point but the limits on materials and/or manufacturing tolerances may have prevented them from working at the time.
The first one is a possible way to eliminate the
influence of scrap flutter
at the head rather than trying to get rid of every bit of it in the tape path. The idea is to mount the heads inside of a capstan/idler. The capstan/idler would need to be large in diameter (I'm guessing 4" or so) and would control the tape speed as it rotated past the fixed heads inside. I'm guessing that the tape would need to lay on a couple of inches of the outside rim of this petri dish shaped idler. A couple of guides before and after would wrap the tape on the idler. The outside rim would have a path of highly permeable material that would need to be extremely thin to maximize flux density transfer to the head inside. Of course, any wow and flutter as well as rumble from the capstan/idler would need to be vanishingly low so maybe a magnetic/air bearing combination could be employed.
All of this won't be practical
unless a head could be devised which is sensitive enough to read everything that's imprinted on the tape from what would be a relatively long distance compared to a head which is in intimate contact with the tape surface.
I would guess that if this has been attempted before that this was a major stumbling block. The reason I think this could work today is the advances in the read/write heads on hard drives. I haven't really looked into this very far but I do know that some no longer contact the disk surface at all now. And it would seem that the "heads inside the idler" would remove the need for the heads to be in the least bit robust.
Idea 2 this one's somewhat linked to the one above
This is an idea for playback only. It's based so heavily on Jamie Howarth's Plangent Process that it could well be an infringement on his patent. For those who don't know, here's a link;
http://www.plangentprocesses.com/The Plangent Process is a speed correction hardware/software package for digital transfers of magnetic tape. It employs the imprinted recording bias as a time constant. Fantastic idea IMHO! It's particularly useful when old tapes which are damaged or were recorded at speeds that either varied or were outside of the normal standards (ie. Kind of Blue). Corrections in speed are done in the digital domain.
So, if we're just talking about playback here, why not use it instead of a crystal oscillator to control tape speed variations? The process
does require a special head to read the bias frequency. This would introduce more scrap flutter in a normal arrangement since this head needs to be before and close to the playback head (the distance and time delay is compensated digitally in the Plangent Process). But, if this head were located inside of the capstan/idler this wouldn't present itself as a problem. It could even serve as the guide that precedes the capstan/idler.
Well, those are my two whacky ideas for today. Please feel free to hack away at them.