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 Post subject:
PostPosted: Feb Sun 20, 2011 8:01 pm 
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Location: ID 83301
Has this guy restored the motor ?


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 Post subject:
PostPosted: Feb Tue 22, 2011 1:11 pm 
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Joined: Apr Wed 09, 2008 3:37 am
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Location: Little Rock, Arkansas
Ken G wrote:
Has this guy restored the motor ?


If he hasn't cleaned and re-oiled the motor bushings, that may be why she's running slow.


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 Post subject:
PostPosted: Feb Sun 27, 2011 5:57 am 
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Joined: Jun Fri 22, 2007 12:54 am
Posts: 902
Location: San Diego
What the idler wheel does is transfer arc length per unit time from the motor pulley to the inside of the platter rim.

In theory, this means that the diameter of the idler wheel does not affect speed. That's it, no further discussion.

* * * * *

Except that many people find that idlers do seem to affect speed. Why?

(1) If the idler is too small, the effective driving surface of the idler is correspondingly reduced. This may result is excessive slip, especially if the surface of the idler is not soft and tacky.

(2) If the idler is either too large or too small, the angle of contact between the idler and the motor pulley and the platter may be all wrong, and again, this may result in excessive slippage. Also, certain angles of contact may tend to "jam" the motor pulley.

(3) If the idler wheel is too high or too low, and the motor pulley is not absolutely cylindrical, then the height of the idler will affect the speed due differences in arc length per unit time measured at the pulley contact point.

(4) If the idler wheel presses against the pulley too hard it may cause the motor to slow down due to excessive loading.

Fred
repairing audio gear since the Pleistocene


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 Post subject:
PostPosted: Mar Sat 05, 2011 7:59 am 
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Joined: Sep Tue 22, 2009 12:34 am
Posts: 135
Thanks for all the help/debate. Even lubricating the motor didn't help. I ended up putting some duct tape on the inside ledge of the turntable platter, thus altering it's diameter, this increasing the speed by a couple of RPMs. Works great!!


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 Post subject:
PostPosted: Mar Sat 05, 2011 10:18 am 
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Joined: Jun Fri 22, 2007 12:54 am
Posts: 902
Location: San Diego
Don't do that.

That's a terrible solution. Put the turntable on a rumble-measuring instrument, and the rumble-figure will be HORRIBLE. Or just watch the movement of your woofer cones if you don't believe me.

(1) Adjust pulley height correctly.
(2) Break down and get a PROPER idler wheel.
(3) Have someone who truly knows what he or she is doing service the motor. You need to fully pull it apart, clean & lube the bearings. Often the rotor shaft needs to be polished with #2000 sandpaper. After reassembly, the top bearing needs a "twist of the shaft" to seat properly.
(4) Examine the power switch and the capacitor in the "little black box." Don't hesitate to burnish the switch contacts (#2000 sandpaper again) and to replace the capacitor (they get leaky).

Fred
owner of the #1 Dual service establishment in Southern California
repairing audio gear since the Pleistocene


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 Post subject:
PostPosted: Mar Sat 05, 2011 5:53 pm 
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Location: Pro Tech, Philadelphia Pa.
Duct tape..... LOL...... hilarious! :lol: :lol: :lol: :lol:

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 Post subject: Re: Idler Wheel Question
PostPosted: Jan Sat 06, 2018 10:51 pm 
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Location: Mount Arlington, NJ 07856
I know I'm bringing up an old post but I have the opposite problem. It's a 78RPM Zenith console that I had cleaned and re-lubricated the motor & all spinning parts, had the idler wheel rebuilt and everything spins freely. Problem is, it one runs too fast!

Any idea's? I do get that the physics are such that the idler wheel diameter does not cause a change in speed but oddly enough, I put two rubber bands around the idler and it brought the speed down to the correct speed. What do you think? Slippage? Could it be that older players were set up for 80RPM? This is actually a bit faster than 80 according to my strobe disk. The player is a Zenith 1942 model 7S682.

I don't know how to solve this problem. Dropping the voltage reduces the torque which breaks the automatic functions. The motor pulley has something on it that slightly increases the diameter. If I remove the set screw and this piece, the player slows down too much.


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 Post subject: Re: Idler Wheel Question
PostPosted: Jan Sun 07, 2018 3:33 am 
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Location: San Diego
The idler wheel transfers ARC LENGTH from the circumference of the motor pulley to the idler wheel, and from there to the platter. Thus the governing factors are motor rotation rate, pulley diameter, and platter rim diameter. Assuming everything lines up correctly, idler diameter ought to be irrelevant.

But that's theory. In the real world, often the alignment of the idler wheel and motor pulley DO produce noticeable changes in the speed. Since the motor is normally mounted on grommets, I always look to see if the grommets are worn out. If they are, the motor will sag. When it sags, two things happen. First, the motor pulley no longer points straight up, so that it doesn't provide a "true" contact surface for the idler. Second, the pulley often sinks low relative to the position of the idler wheel. I've even seen it where the pulley climbs up off the 45 portion of the pulley, and onto the 33 part because the motor has sagged a good 1/8 inch.

These "errors" normally cause the platter to go slow and have poor transfer-torque. But your 78 player is going fast, and doesn't have a multi-speed pulley. And you say that dropping the AC voltage doesn't help. Hmmmm.

Once in a while, at Classic Audio Repair we need to take fine sandpaper and reduce the diameter of the motor pulley. If you reduce the pulley diameter by 2%, the speed will normally reduce by 2%. This is a last ditch situation. When I do this, I make a collar around the top of the motor with slightly moistened blue shop towels---this to capture metal filings from the pulley.

Also, and I presume you've checked this, but I'm still going to bring it up, often motor pulleys get a crusty residue from caked-on dead rubber from the idler. This increases the pulley diameter AND since the build-up is not "machinist accurate", it hugely increases the rumble. The cure is nominally to clean the pulley with pure alcohol or acetone. Unfortunately, this doesn't always work. If a crusty build-up won't come off with solvent, take a soft wooden stick (I prefer chop sticks and I trim the ends with a knife to a 45-degree angle). Use the stick to scrape the deposit off the pulley.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

NOTE TO OLD AUDIO TECHS LIKE ME --- In 1973, I bought a book about servicing tape recorders by Middleton. I can't thank him enough. He said that to remove crusty deposits from tape heads (where solvent didn't quite do the job) you should use a "lemonwood stick". I've kept a supply of ice-cream-bar sticks and chopsticks at my repair bench for 45 years! They work on motor pulleys for the same reason they work on permalloy tape heads---they're softer than the metal and don't abrade.


Fred

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 Post subject: Re: Idler Wheel Question
PostPosted: Jan Sun 07, 2018 6:46 pm 
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Joined: Feb Mon 04, 2013 6:55 pm
Posts: 558
a player that runs a little slow, but steady, is usually caused by old gummy lubricant in the motor bearings. 2 pole motors have very little torque, and any extra load will make them run slow. the bearings are usually porous bronze, and may need repeated soakings in laquer thinner to get all the old gummy stuff out. armature alighment is critical too, if thats off there will be binding and it will run slow. make sure its spinning absolutely freely when you reassemble it, keep trying unti it is.


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 Post subject: Re: Idler Wheel Question
PostPosted: Jan Sun 07, 2018 7:55 pm 
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Joined: Jun Fri 22, 2007 12:54 am
Posts: 902
Location: San Diego
His platter was turning too fast, not too slow.

Fred

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 Post subject: Re: Idler Wheel Question
PostPosted: Jan Mon 08, 2018 3:04 am 
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Joined: May Sat 06, 2006 4:03 am
Posts: 2942
Location: ZIP 23831 South of Richmond, VA 25 miles down the pike.
As far as you know you did get the correct idler wheel rebuilt?

Bill J.


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 Post subject: Re: Idler Wheel Question
PostPosted: Jan Sat 20, 2018 3:10 pm 
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Joined: Aug Fri 09, 2013 1:01 am
Posts: 470
Location: Mount Arlington, NJ 07856
Yes, in fact I had him rebuild my original wheel and I scribed a mark on it to be sure I got the same one back. The gentleman was extremely nice and the quality is very good This makes me wonder if this changer was like this when new.


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 Post subject: Re: Idler Wheel Question
PostPosted: Feb Thu 08, 2018 8:30 pm 
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Posts: 63
Well here's a good TRICK for Idler wheels!!
The problem with Idler wheels in older units is the Rubber losses traction because the Rubber is either dirty or the Rubber has begun to go hard as rubber does with age ,heat and cold.
To fix the problem of hardening Rubber so the Idler wheel will get correct traction again you just soak it in KY Jelly over night and the Rubber will be like new the next day.
I first learnt this trick with KY years ago when restoring seals on vintage motors and gearboxes. Works great on Idler wheels!
Pete

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Vintage Tv's ! When Television was worth watching !


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 Post subject: Re: Idler Wheel Question
PostPosted: Feb Fri 09, 2018 2:47 am 
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Joined: Jan Wed 16, 2013 12:04 am
Posts: 1206
Location: 77001
vintage pete wrote:
Well here's a good TRICK for Idler wheels!!
The problem with Idler wheels in older units is the Rubber losses traction because the Rubber is either dirty or the Rubber has begun to go hard as rubber does with age ,heat and cold.
To fix the problem of hardening Rubber so the Idler wheel will get correct traction again you just soak it in KY Jelly over night and the Rubber will be like new the next day.
I first learnt this trick with KY years ago when restoring seals on vintage motors and gearboxes. Works great on Idler wheels!
Pete

Pete:
How long does the re-conditioned rubber effect last ?

Hotwax


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 Post subject: Re: Idler Wheel Question
PostPosted: Feb Fri 09, 2018 3:48 am 
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Joined: Dec Fri 16, 2016 2:58 pm
Posts: 63
Long long time!
If you look up KY gell for Rubber conditioning you will see , its a old trick many people use particularly in vintage motorcycles.
But i use it all the time on turntables and Ilder wheels.
It will condition any type of rubber.
The worst Idler wheels are the Red rubber ones, they seem to rot and go hard much faster than the black rubber.

Pete

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Vintage Tv's ! When Television was worth watching !


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 Post subject: Re: Idler Wheel Question
PostPosted: Feb Fri 09, 2018 4:00 am 
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Joined: Dec Fri 16, 2016 2:58 pm
Posts: 63
Transmission gearbox Seal conditioner will also work . More costly though.

Pete

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Vintage Tv's ! When Television was worth watching !


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 Post subject: Re: Idler Wheel Question
PostPosted: Feb Sat 10, 2018 11:39 pm 
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Joined: Aug Fri 09, 2013 1:01 am
Posts: 470
Location: Mount Arlington, NJ 07856
Very interesting and thanks. I have another record player I've been itching to get going on. I'll give it a try.


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