Quote:
Originally Posted by ricard
Quote:
Originally Posted by DMcMahon
So I now assume that when the the motor shaft rotation speed gets to a certain level that centrifugal force will push up the sprung loaded plunger and open the G contacts. I say assume, it has got to be something very similar otherwise the contacts would never open. Looking forward to seeing the plunger lift up in operation.
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That is correct, the idea is to supply the motor with a higher voltage while it is starting up, and then go to a lower voltage once it has reached its proper speed, I'm assuming to minimize motor power consumption and hence heat. This mechanism is only operational at the higher speed (7 1/2) however; at 3 3/4 the lower voltage is used all the time.
Can't really see in the picture, but it looks like it might be missing a little plastic top on the plunger to avoid it short circuiting the contacts to ground. It should be white-ish in color. |
I don't think it's anything to do with power consumption/heat. The brief application of higher voltage will be to overcome the starting inertia of the take-up spool - otherwise the capstan will have fed an amount of tape through before the take-up spool has reached sufficient speed to take the tape up - thus forming a loose tape loop that suddenly gets snatched up when the spool reaches speed. The larger (heavier) the spool and the greater the capstan speed, the greater the problem. It becomes a huge problem if the machine is using 10.5 inch metal NAB spools, and is feeding tape at 15 i.p.s. But the problem would still be there at 7.5 i.p.s. and with smaller spools.
That's my take on it, anyway!
Mike