Hi Kip,
I think that's a great example of the right bearing for an application.
Athan specializes in rebuilding motors for the pro audio/broadcast industry.
In the case of reel motors, smooth operation at different rpms and the forces that full reels of tape exert on the bearings are some of the considerations. Heat must be minimized for long life and consistent back tension on the tape during play are othes. If you think about what normally happens at the bearing level, you rewind the tape at a relatively high rpm putting maximum load (full reel) on one bearing to the other (take up then supply reel). Then almost immediately, you put the machine in play where the load is a fraction of what it was. So, not only are you looking for a bearing that produces a minimum of heat but it's also important that it dissipates what heat was produced quickly. The sensors for the adjustment of tape tension/speed are located in these motors also so it's important that the bearings can react quickly or the correction circuits will be constantly hunting for the right correction.
So in this case the bearing need to be able to do some heavy lifting (with what is always an unbalanced load) then switch to a delicate task.
In comparison, the capstan motor is usually attached to a large, heavy flywheel that smooths the speed so the load is ultra consistent. It moves at a slow steady rpm. It also need to be very smooth but for an entirely different reason. You're trying to minimize the amount of noise that the bearing makes so it isn't transmitted to the tape via the capstan. It also need to be able to react quickly during speed corrections.
So a bearing here needs to be able to take a heavy, very consistent load at low rpm's with as little noise a possible.
Someone like Athan has years of experience on which bearings are best in each of these applications within the confines of the particular decks design. Choosing the right bearing would make or break a company who does work on machines that belong to some of the best ears in the world.
On another note, Doc makes a really important point.
Keeping you tape path clean is critical for getting the best sound and maximizing the life of you tapes. But be very careful about how you do this. Dipping a swab into a bottle of alcohol or head cleaner then wiping it on the tape path bearings will eventually ruin them. Actually, I suspect that most noisy bearings are the result of this.
What I do is after dipping the swab, I suck on it,.. no-no just kidding,.. I roll the swab on something absorbent so it's just wet with the solvent and not dripping with it. You're just cleaning the surface of stuff so take it easy. And just to be sure, I clean the parts with bearings last.
Like I said before, just how critical these particular parts are depends of how refined the machine has be designed.