Thorens TD-124 running too slow with Audiosilente idler wheel (but runs fine with original idler)

[borchee]

Diameter of idler will not affect speed...

The solid/rigid/metal part won't, but because of the tyre being soft/elastic, the active/working diameters are not equal where it meets the pulley and the platter.

The difference lies within the diameter of the wheel and diameter of the wheel with tyre - these are two gears. If this can cause the unknown speed difference OP claims, I have no clue.

 

[cafe latte]

The solid/rigid/metal part won't, but because of the tyre being soft/elastic, the active/working diameters are not equal where it meets the pulley and the platter.

The difference lies within the diameter of the wheel and diameter of the wheel with tyre - these are two gears. If this can cause the unknown speed difference OP claims, I have no clue.

An idler wheel could be half the size it still would not affect the speed.
The only reason a,different idler wheel affects the speed is if the rubber it too soft you get creep slowing the speed down, harder less creep, slip and it speeds up, diameter has nothing to do with it.
Chris

 

[chrisinsc]

If there is a belt driving a smaller pulley on the idler shaft the ratio can be changed.

The pulley on the motor can be flipped for 50hz electrical systems. I just refurbished one of these with the papst replacement motor on it. Even with meticulous cleaning and lubing it takes 30 minutes running to come up to speed where it can be adjusted in to 33.333…rpm’s. After two hours running it will stay at the adjusted speed for as long as you want to run it. It’s a great piece of gear if you run a radio station. It sounds great and has an SME 3009 III arm with a Grado GF3 cart and new red 3 stylus. Love the clutch platter for changing records.

 

[tnsilver]

I have the Audiosilente idler wheels in my two Thorens 124 ( Mk I & Mk II )and I have never encounter any problems whatsoever

Me too. Never an issue.

 

[hirscwi]

I've installed Audio Silente idler wheels in at least 14 124s. Always give superior results with no modifications needed to the wheel. You may want try adjusting the eddy brake to correct speed.

 

[gadget73]

The solid/rigid/metal part won't, but because of the tyre being soft/elastic, the active/working diameters are not equal where it meets the pulley and the platter.

The difference lies within the diameter of the wheel and diameter of the wheel with tyre - these are two gears. If this can cause the unknown speed difference OP claims, I have no clue.

Speed adjustment on an ROK relies on this. The more you smash the motor into the idler, the slower it goes.

So yes, the durometer is important

 

[cafe latte]

I've installed Audio Silente idler wheels in at least 14 124s. Always give superior results with no modifications needed to the wheel. You may want try adjusting the eddy brake to correct speed.

If the hardness of the rubber was correct there would be no need to adjust it.
Chris

 

[borchee]

An idler wheel could be half the size it still would not affect the speed.

This might be true, but it's not a given. If the tyre is of the same thickness and compressed/deformed the same way as in the idler wheel twice the size, the gear ratio has changed.

Of course, if the compression (the active diameter) at pulley and platter contact points is equal, then the gear ratio remains unchanged and the idler behaves like an idler - transfering rotation from one shaft to another 1:1 and not acting like a gear.

This is as counterintuitive, as speed changes with belt thickness (valid for two pulleys of different diameters).

 

[cafe latte]

This might be true, but it's not a given. If the tyre is of the same thickness and compressed/deformed the same way as in the idler wheel twice the size, the gear ratio has changed.

Of course, if the compression (the active diameter) at pulley and platter contact points is equal, then the gear ratio remains unchanged and the idler behaves like an idler - transfering rotation from one shaft to another 1:1 and not acting like a gear.

This is as counterintuitive, as speed changes with belt thickness (valid for two pulleys of different diameters).

You can change the speed of the table by adjusting idler wheel tension in this way.
Commonwealth tables have two lugs on the idler spring and adjusting these you can fine adjust speed.
My comment was something else. People think that grinding an idler to get to fresh rubber will affect the speed due to the idler being smaller, but this is not true, this was my point.
Chris