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Thorens TD-166 MK II and 78 RPM

B

barnett1

New Member
Hello to all the Thorens experts out there. I have a TD-166 MK II that I have owned since new. I have recently gotten back into stereo gear after several decades (life gets in the way). My Thorens TT has become the 3rd of my three current tables. I also have a collection of vintage crank phonographs (Edison, Victor Talking Machine). What I would like to do, if possible and reasonable, is to modify my TD-166 to play my 78 RPM records. I understand about the variability of 78 recording speeds, etc., and I'm not too concerned about that. I'm also aware of the need for a 78 RPM stylus. I want to be able to play the old shellac 78's on my good system and I'm just looking for better fidelity than is produced by my vintage machines. I'm willing to give up one of the current speeds (e.g., 45 RPM) to make the 78 RPM work if necessary. Any thoughts, suggestions, guidance?

Thanks in advance
 
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What governs the Thorens speed is the locking to line frequency (synchronous motor) and the diameter of the motor pulley (transmission ratio). Unless you obtain or manufacture a pulley that's the right diameter for your line frequency and 78 RPM, it's not going to happen b/c it's too much hassle. In such case you'd also want the other speed to work, so the tapering between the two steps on the pulley must be adjusted for the speed change mechanism to keep working, and that's tough to do!

The other option is hooking up an external speed controller, which would circumvent the stock Thorens locking to line frequency, and supply its own - such that with the right combination of pulley diameter, it ends up with the platter spinning at 78 RPM. This was probably done before, but it kinda defeats the whole idea of simplicity behind the TD design. It's not cheap either.

The bottom line is, this is not the right turntable to play 78's.

BTW: Welcome to AK!
 
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Thanks for the welcome! The approach I had more in mind was changing the electronics (capacitor/resistor) to tey to get the motor to turn faster. I've seen the schematic and I believe that a 0.33uF capacitor comes into play when 45 RPM is selected. Or do I have that backwards and it's for 33 not 45?
 
No, it's not backwards, it's totally wrong. The large capacitor is a phase shifter which is responsible for the motor turning in the desired direction (otherwise it would spin in any arbitrary direction), the small capacitor is an arc-suppressor for the switch, and the resistor is only used in 220V locations to drop the voltage for the 110V motor. There's nothing you can do the electronics to achieve 78 rpm. I'm not even sure if the rudimentary components on the TD-16X power supply qualifies as 'electronics'. The speed stability magic is really limited to the synchronous motor and the number of poles within it, and it always runs on anything between 90V - 130V without affecting the speed.
 
Note that some of the later Mk-II's are running on AC/AC wallwart power supplies (16V - 20V) and are equipped with lower voltage triangular Sonceboz motors, but it's the same principal as the earlier high voltage motors (i.e 'synchronous motor'). That's why the exact voltage supplied by the wallwart isn't really important, as long as it's within a range.
 
I'm not prepared to give up yet. :) If the drive pulley is increased in size for the appropriate ratio and a longer belt is used, it could be converted into a dedicated 78 machine. The motor pulley mod could be accomplished by putting a correctly sized sleeve over the existing pulley. And the length of the belt necessary could be calculated. Is anything I said there incorrect?

I want to keep my Thorens, but as I said, it's 3rd out of three at the moment, so I would really like to figure out a way to get this to work.
 
The belt length has nothing to do with it, but you could experiment with the sleeve idea. I suspect it would prove problematic when it comes to speed change, but if you solve the 78 rpm pulley diameter issue, it's going to be marginal. For a dedicated 78 machine it's not an issue at all. Good luck!
 
The pulley diameter would have to increase by about 70%. My concern about the belt is just that it might be stretched too tight and put excess strain on the motor bearings. And yes, in this approach I would give up both 33 and 45 for 78. Trying to get multiple speeds to work like this would probably be far too difficult.
 
The expensive option is to get a TD 125 MK. II and an Andyjay control board that replaces 16 2/3 with 78 rpm. Or just get a TD 126 but avoid the Mk. III.
125/126 are better turntables than 16x/14x too.
 
Yes I saw the posts about the TD-125 mods and using a 126. My proposed solution might end up not being much cheaper, but I at least have most of the pieces already, including an Ortofon cartridge that can accept a 78 stylus. And I have the attachment to my 166.
 
barnett1 said:
The pulley diameter would have to increase by about 70%. My concern about the belt is just that it might be stretched too tight and put excess strain on the motor bearings.
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Transmission ratio wise the belt plays no role. Don't worry about extra stress. Those belts stretch on their own faster than any of us likes them to. My concern would be, for such a large pulley, the gap to the belt guard at the end of the speed change lever. If there's not enough room, you may have to discard of the lever. You're not gonna need it anyways.
 
I just took a quick look and you are correct. There may be a space issue there. I haven't worked out the exact dimensions yet. But for a dedicated 78 machine, the speed change lever could be removed if necessary.
 
Taking a piece of reinforced silicone tubing, 5/8" ID, 1" OD and about 1/2" high, and wrapping some vinyl tape around the outside to increase the OD to 1.065" creates a bushing that fits perfectly on the motor pulley and drives the platter at 78 RPM. The startup takes several revolutions to overcome the added mechanical disadvantage of the larger motor pulley, but once up to speed, the speed is consistent. This method also allows the motor pulley clutch to remain and provide a gentle start.
 
barnett1 said:
Hello to all the Thorens experts out there. I have a TD-166 MK II that I have owned since new. I have recently gotten back into stereo gear after several decades (life gets in the way). My Thorens TT has become the 3rd of my three current tables. I also have a collection of vintage crank phonographs (Edison, Victor Talking Machine). What I would like to do, if possible and reasonable, is to modify my TD-166 to play my 78 RPM records. I understand about the variability of 78 recording speeds, etc., and I'm not too concerned about that. I'm also aware of the need for a 78 RPM stylus. I want to be able to play the old shellac 78's on my good system and I'm just looking for better fidelity than is produced by my vintage machines. I'm willing to give up one of the current speeds (e.g., 45 RPM) to make the 78 RPM work if necessary. Any thoughts, suggestions, guidance?

Thanks in advance
Click to expand...

Can't be modified. Not a suitable machine for 78 RPM. Why not a Lenco for 78 RPM work, the L-75 has lots of variable speed range.
 
I have already successfully modified the TD-166 MK II by adding the motor pulley bushing, turning it into a dedicated 78 RPM turntable. Cost < $10. Buying a Lenco (or any other turntable) would require a significantly higher investment....
 
barnett1 said:
I have already successfully modified the TD-166 MK II by adding the motor pulley bushing, turning it into a dedicated 78 RPM turntable. Cost < $10. Buying a Lenco (or any other turntable) would require a significantly higher investment....
Click to expand...

Lenco can go over 90 RPM (and some shellac plays at that speed for correct pitch). Which is why I recommend them for vintage disc playback.
 
barnett1 said:
Taking a piece of reinforced silicone tubing, 5/8" ID, 1" OD and about 1/2" high, and wrapping some vinyl tape around the outside to increase the OD to 1.065" creates a bushing that fits perfectly on the motor pulley and drives the platter at 78 RPM. The startup takes several revolutions to overcome the added mechanical disadvantage of the larger motor pulley, but once up to speed, the speed is consistent. This method also allows the motor pulley clutch to remain and provide a gentle start.
Click to expand...
Nice. :) Sounds like victory. For a dedicated 78 machine, it sure sounds like an economically viable success. The reason the 78 mod sounds so awkward and inconceivable with a TD-16X model, is because a 1" pulley step, (plus change) is gigantic and can hinder the speed change mechanism useless - unless designated a single speed machine. Also, at 78 RPM (technically should be 78.26 @ 60Hz) is fast enough to induce vibrations on the stock suspension system, which was not designed for such high speed. Nitpicking aside, I don't think the content of 78 records is up to snuff with the Thorens standards anyway, so what the heck! This sure sounds interesting to me.
 
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