Garrard 301 60Hz pulley

[aoroa]

I am wanting to make a 60Hz pulley for a Garrard 301 and wondered if anyone could help with the diameter measurements for each of the 3 speeds.
I would need them in thousands of on inch if possible.
Thank you very much if you can
Rod

[405man]

I have one somewhere and when I find it I shall measure it and let you know

Stuart

[EC8010]

Another factor you need to take into account is that the magnet in the eddy current brake demagnetises over time (we are, after all, talking about a consumer product over thirty years old) and that means the motor runs fast, so the pulley needs to be even smaller than the original specification if the turntable is to run at the correct speed with the fine speed control at centre setting. As an example, my 301 runs about 2% fast.

I measured its original 50Hz Garrard pulley:

0.25345"
0.34435"
0.59865"

A -2% 60Hz pulley would be proportionately smaller:

0.2070"
0.2813"
0.4891"

I measured the motor shaft as being 0.1929", so that means you have a 7 thou wall thickness on the 33 1/3 step. Martin Bastin made me one of these, but I wouldn't care to try myself!

[aoroa]

Thank you for that. I assume you took 5/6 of the 50Hz pulley minus 2%.
I wasn't sure that this would give me the correct answer but apparently so.
I hadn't thought of the magnetism degradation so thanks again
I think the wall size would be 70 thou not 7.
70 thou I can handle!!!
Regards
Rod

[EC8010]

That's right, 5/6 minus 2%. But I'm afraid I'm right, it really is 7 thou wall thickness...

Edit: This thread ought really to be in the "Analogue" forum. I'll move it.

[valveitude]

But I'm afraid I'm right, it really is 7 thou wall thickness...

Now thats gonna be fun

[aoroa]

Hi again
2070 minus 1929 =141 \2 =70 (I think)
Also how do you get such accuracy in your measurements?
Regards
Rod

[aoroa]

Oops you are right - sorry about that.

[EC8010]

Originally posted by aoroa
Also how do you get such accuracy in your measurements?

When I bought my lathe I worked in Imperial measures, but I felt it was time to change, so I bought a metric lathe. That meant I needed a metric micrometer, and when I looked, digital micrometers were just appearing at the top end of manufacturer's ranges. They all had an "inches/mm" switch (which was incredibly useful to me at the time). As they were expensive, I thought I might as well get something for my money and I bought a micrometer with a resolution of 0.00005".

[bbtv]

Hi I have another suggestion to make regarding correcting the Garrard 301 speed, e.g. wrong pulley size or loss of magnetism in the eddy current brake. It may seem a bit over the top, but it is the perfect solution that I have tested. Make up a simple adjustable 50Hz or 60Hz Wien bridge sine wave oscillator
See:-
http://www.members.iinet.net.au/%7Eq...udio/TTPS.html

and feed it into an amplifier (40W into 8ohm load minimum I would suggest) and then connect the output to the secondary winding 12V (50Hz) mains transformer in reverse. The primary winding should now be connected to the turntable motor. Before turning on check the output frequency of the oscillator with a frequency counter or an oscilloscope. Turn the volume control to minimum. Connect a AC volt meter to the transformer primary and turn amplifier on. Slowly advance the volume control untill the voltage is reading 110V or 220V depending on transformer/motor tapings. The turntable should now run and the speed will adjustable by varying the oscillator frequency. Warning do not adjust the frequency down by more than 5% (47.5Hz).
I am thinking to make a simple module using a class D amplifier IC in bridge mode and a 19V laptop power supply. Any suggestions would be appreciated?