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Vintage turntable running fast, any ideas?

I got a Pioneer Pl-12 turntable from a friend who had it stored away for years. I cleaned it up but have found that some voices have a higher pitch compared to the CD version. I tried the free strobe disks and they verified my fears about the platter turning (I assume) too fast. I also measured similar songs from CDs and albums, and the albums always finish sooner. From some rough time estimates, the turntable is running about 3% too fast.

Looking from the bottom side up on the turntable, there are no adjustments and very little electronics at all. The only electronics are: the motor with a few wires running to it; an enclosed switch to select 115/230 voltable, and a somewhat large capacitor (I think). The "capacitor" has a rating of 0.1 uF and some serial numbers.

I suspect the "capacitor" is old or burnt or whatever. I doubt the voltage switch is the prolem, nor the motor, but who knows?

Any ideas? I have a voltage meter so I can measure the usual volts, ohms, or ampere, but I don't have an oscilloscope to measure frequency.

Thanks for any ideas,
rrick
william7
51 posts
 
You better hurry up and catch it but if you wait for a while it will slow down the older it gets
rrick OP
23 posts
 
There is an arm that moves the belt between two different diameters on the pulley. My theory was if it was getting in the way, it would slow down the turntable. Right now, it doesn't look like it affects the belt much.

If I want to physically change the dimensions of the turntable, I have two choices. Make the platter larger or the pulley smaller. Since the pulley is so much smaller, I probably sand it down.

What's weird to me is that the thing runs fast. I didn't expect to run into an old turntable with a hot to trot motor. I'll make sure is has lots of oil and let it run for a day or two. Maybe that will cool its heels.
viridian's avatar
viridian
4,184 posts
 
Congrats on having a good sense of pitch. Most who call themselves "audiophiles" have very little sense of pitch from my experience. I have listened to many ultra high end systems in both shops and private homes where the tables were running well off speed. If the motor is tied to line voltage and that is 115V and your line voltage is running at 118.45V voila you are 3% fast. Seems the one solution would be to listen during the week, preferably in the summer when typical house voltage sinks or buy a variac. Of course that won't help if the motor is tied to the frequency of the line....which also varies. Why not just go down to Goodwill and try again? There's more cool tables and tuners down there than you think.
jameswei
795 posts
 
Could it be that one of your parts is a wrong-size replacement that got put in sometime a long time ago? It sounds like the pulley could be a too-big replacement. Or, the belt (which would have been the first thing to wear out and be replaced) could be too fat, making it not fit snugly into the "V" of the pulley, hence to rotate around a slightly larger circle than it should. Good luck.
tmcroy
25 posts
 
You could try wiring an ordinary light bulb in series with the motor - be aware that it needs to be in a safe place as they are reasonably easy to break and of course a broken light bulb is an electric shock hazard - also remember they give off heat.
The smaller the wattage of the bulb you use, the more it will slow things down and vice versa.
This is in fact simply a current limiting resistor. Used it on my old garrard 401 as the speed control on those is a magnetic brake, which does the sound no good at all. Eventually I got round to machining up a smaller motor drive spindle - didn't sound any better than the lightbulb!
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