On Wednesday, December 17, 2014 12:53:27 AM UTC-5, wrote:
I'm working on my old Ampex 4460 reel to reel machine. (work is slow), and I'd like to listen to some of my old tapes. I cleaned and lubricated it, demagnetized the heads and put a tape of some familiar music on, and I thought it seemed a bit slow. So I repeated it with other tapes and then followed with an Ampex frequency response alignment tape. The scope was calibrated to 1.0ms off the 1KHZ square wave output and then I looked at the the 1KHZ sine wave off the tape. The period was approximately 1.40ms which appears to translate to 714HZ. Truly hard to believe that it's running that slow, but I don't think that the equipment is lying.

So I next got out the Strobeotac and put it on the motor capstan. The motor is rated for 1850 RPM at 115V, and it's running rock solid at 1795. I tried loading it while watching the speed and it remains steady, so it doesn't appear to be a load problem. Could such a slight motor speed reduction cause a 25 percent reduction in the frequency of my 1KHZ test tone off the tape? It doesn't seem possible, but I don't know.

The motor has a label that reads that it uses a 3.0UF 330V capacitor. I haven't investigated this yet, but with four wires going into it I figure that the cap must be on the chassis somewhere. I wouldn't think that a cap problem though would cause my RPM's to drop 55RPM would it? Oh and I have no service manual, however I don't think that service manual would do me much good with this problem anyway.


If anyone has any thoughts on this I'd sure appreciate hearing them. Thanks, Lenny

To answer your questions Mike yes there is a flat belt from motor pulley to capstan flywheel, (see further explanation on that below). The load test on the motor was putting a drag on it with my finger as it was turning. It had no trouble maintaining speed as observed with the strobe tach. i don't understand what you mean when you ask if the capstan has to turn the "full spool". As far as helping manually there really is no way to help manually other than by decreasing the hold back tension. I tried that too but it didn't make much difference. What follows is some further information.

One other thing that I didn't mention was the the main drive belt. It is a flat belt which is roughly 2.0mm thick and has a circumference of approximately 35cm. The other belts are basically just different sized O rings which only needed the slick stripped off of them to expose some good grippy rubber. I had to do that with the capstan pinch roller as well. I used a bit of lacquer thinner on the belts and sand paper and thinner on the roller too to get to some good rubber

The OEM flat belt though was very tired and had "assumed the position" of an oval from sitting in one position unused for so long. I couldn't find anything around here having that circumference that was 2.0 mm thick so as a temporary measure I substituted a much thinner belt. There is a very slight amount of wow which can be seen when looking at the capstan flywheel with the strobe using this substitute belt, and I'm guessing that it could be stretching back and forth ever so slightly as it spins, but you really don't notice it on music and it's only temporary until I can find something a little more appropriate. I wouldn't think that a thinner belt would contribute to a speed error, or am I wrong in making that assumption? Lenny