Hi,
Thanks for your remarks.
during fast wind, if there is no power in the tape tension assemblies the reels would not slow down and stop at the same rate. The reel with the least amount of tape on it would stop first, and the reel having the most tape is heavier, so it would keep on spinning and spilling its contents all over the place!
Again, as far as Revoxes G36, A77, A700 and B77 are concerned, they are designed so that when the Stop button is pressed, power is completely taken off the reel motors. The mechanical brakes do all the stopping with no contribution from the motors at all. Naturally, this works exactly the same way when power is removed from the machine altogether.
Tape spilling is avoided because the design of the brakes makes certain that braking force is always greater on the trailing reel than the leading reel. This is achieved by the wrap of the brake bands around the brake drums, which makes for greater braking force when rotating in one direction than the other. In effect, the drum "wraps" the band around itself when rotating in one direction, increasing braking force, and "unwraps" the band when rotating in the other direction, reducing braking force. This is much like old-fashioned leading-shoe drum brakes on cars, which augmented driver effort by the way the brake shoe was hinged. The effect worked the other way around when the car was moving in the reverse direction - much greater pedal effort was needed for the same braking force. Don't ask how I found that out...
The difference in tape load is compensated by the fact that the lighter reel spins faster, because the circumference of the tape pack on it is shorter, and the heavier reel spins more slowly because the tape pack on it has a longer circumference. This reduces the difference in the mechanical energy between the two reels - a lighter reel spinning faster has about the same mechanical energy as a heavier reel spinning more slowly. This makes it possible to always brake harder on the trailing reel using the simple mechanical trick Revox pulled with the brake band wrap, no matter what the difference in tape load between the two reels.
This is also one reason why, on your Revox, you should always have reels of the same type on both spindles. Never mix 7" with 10 1/2" or plastic with metal or you will spill tape when stopping after fast wind or rewind. Again, don't ask how I found that out. The other reason is to do with tape tension and is beside the point of this discussion.
I am mentioning Revoxes because I'm very familiar with them and they are quite well known, but I would venture to suggest that most consumer machines from the open-reel era, even high quality ones like Revoxes, had simple mechanical brakes that were designed to always keep tension on the tape by braking harder on the trailing reel. Electronic trickery with the reel motors was costly back when open reel was mainstream - and completely impossible in the earlier valve (tube) era. Mechanical ingenuity, though, was
de rigeur.
With best regards,
