I’m gathering the results of my Thorens TD-135 research and restoration here for future reference as I work on a well used example that probably had a long institutional career. This page will be changed as I gain experience, find new resources, and correct mistakes. I am not an expert, have owned only this Thorens.

Information for the TD-135 is scarce because of its relative low sales and esteem compared to famous big brother TD-124. I can see these being marketed for home use and libraries and amateur radio stations. The 135 and 124 share some drivetrain parts –including the motor (possibly with smaller coils than the 124 Mark I and positively smaller than the 124 Mark II), belt, pulleys and idler wheel– so potentially useful information about the 135 is often buried in online threads or pages dedicated to the more popular 124.

Also, the motor pulley has two sizes for 50 and 60hz, so sometimes belt sizing becomes confusing.

A 135 is over 50 years old by now, so some repair and maintenance was expected. The work I’ve done so far has resulted in much improved sound and much lower mechanical noise, encouraging further efforts.

Some reports of Thorens restoration suggest that the focus and solidity of sound as the best indicator of the health of the drivetrain. In my limited experience this is perfectly correct: I have immediately noticed missteps by paying attention to sound quality.

However, after building a heavy plinth and working with its modular design to minimise rumble, it has become more difficult to discern the “needs” of the drivetrain. I therefore suggest tuning the drivetrain while the table is mounted in a hollow box –as they often were in institutional use– then moving it to the heavy plinth.

Also, in the course of working with the motor, I built a “giraffe plinth”, consisting of a top plate screwed to 11″ 2 x 2 legs so that I could adjust the motor alignment while running under load. This works well for the purpose, but is nearly as quiet as the heavy plinth.

Tonearm

The BTD-12S tonearm that came mounted is an earlier iteration of the TP-14 that came with the TD-125. Because it is mounted on the table without an armplate, it has a different bearing arrangement than the separate BTD-12S tonearm which was mounted to the 124, so the diagram in that manual is not completely correct or useful for the 135. There is no downloadable manual in English for the BTD-12S, but there is one available for the TP-14, and it has useful information for working with the 12. It also assumes an armplate mount. Both manuals are available at vinylengine.com.

The tonearm is meant to be run without any lubrication. The manuals in German and French say so if one can read them and find that imprecation buried in the middle with no emphasis. The manual for the 14-series tonearm also specifies no oil. My arm was both corroded and had been lubed. I polished the races and installed new bearings in the tonearm base. The balls in the upper race were no longer round from corrosion, causing intermittent skip on different records and at different places and not repeatable in successive plays of the same record.. The skipping is gone after the refurb and the arm tracks well.

That said, it is not easy to set up; even experienced Thorens restorers have told me that they find these a challenge, and there are no instructions for reassembly that I can find. I may include a diagram or instructions for that at some point. Before taking the arm apart, I strongly suggest making a diagram of the layers of washers and springs, and doing the work over a tray which will catch the 18 bearings as they fall out, since they are not retained. Any attempted adjustment of the vertical shaft at first will result in the arm falling apart and the bearings dropping out. I used a lid from a storage container underneath and it worked well.

The bearings in the base of the tone arm are 7/64″, each race takes 9 balls. Local bearing houses did not stock that size. For replacements I found some hardened stainless 440 tight-tolerance balls at McMaster Carr which fit well and have a better chance of surviving in a humid climate without lube. The races appear to be bronze or brass and polished nicely with little effort. I have an original drawing of the arm and they did indeed spec 7/64″ balls and not a metric size. I have been told that at the time Thorens had them made especially for this arm.

The reason for the difficult adjustment is that there are several things which must be aligned simultaneously. When the cuing lever is used to lift the arm, it also presses the bearing pack together to “brake” lateral arm movement, so that when cuing back down the arm should land in the same place. If this is not correct the arm will swing slightly when lifted and set down. Yet when the arm is set down the braking must not be applied. so there is a sub-1 mm difference between being held and being let go. The slack –so that the arm does not wobble–is taken up by a light spring which is part of the bearing stack on the bottom side. There are multiple places for adjustment –the lever, the bearing shaft collar, a cue height limiter on the arm base– each affects all the others, none can be found correct without a trial. It is painstaking work to get that adjustment right, in the end it’s easier to manually set the needle down.

The manual for the TP-14 has a procedure for calibrating the VTF adjustment lever on the arm. The suggestion is to balance the arm first with the counterweight, then set the lever to the desired VTF. To calibrate the lever, one uses 1g and 3.5 g settings and turns an allen-head bolt to match a scale. I found the settings to be wildly variable going up and down the scale, and also as the arm tracks across the playing surface. Adjustment of the bolt was not adequate to get the lever setting close to the actual VTF, in fact it made little difference at some settings. So I decided to bypass it by unhooking the end of the spring from the lever.

I weighted the arm and use the counterweight and a scale to set VTF. To my ears this made a large improvement. And it probably saved wear on the cartridge and records. To be fair, the spring and interior of the arm shroud were corroded when I received the table.

I will note that I was also not aware of some binding in the lateral bearings at that time, and have since loosened those somewhat and polished the cones. This resulted in improved tracking and the statically-set VTF is consistent across the arm travel. It may be that the bearing adjustment would make the dynamic balancing system work correctly, but it’s easier and more stable for me to continue to use static balancing for now.

Drivetrain

The drive for the TD-135 is belt/idler. There is a pulley on the motor shaft which drives a belt to a stepped aluminum wheel that then drives an idler wheel at four speeds depending upon alignment. In between each speed setting is a neutral which pulls the idler wheel back to allow it to move vertically to another speed position.

The motor is not synchronous. There is an eddy current magnet outside the idler wheel, fine-adjusted by the inner star control on the speed selector. For coarse adjustment the platter must be removed and a holddown screw loosened. The magnet must be held closely while loosening the screw, then moved very slightly, the screw tightened, platter reinstalled, and measurement taken again.

For oiling the control mechanisms and the platter bearing, I used light turbine oil. The platter now takes an average of 01:20sec to spin down from 33 1/3.

I disassembled the motor and applied the turbine oil to its bearings. There is a procedure for cleaning out the sintered bronze bearings by baking them.To remove the bushings and felt washers for cleaning and relubing, two rivets on each end of the motor housing must be drilled out, they will be replaced by small machine screws for reassembly. One suggestion is to swap top and bottom bushings because the top one gets more wear from being under load by the belt.

I used careful and light applications of brake parts cleaner, absorptive cloths, and patience. The previous lube was green, and it seeped out as I worked. I worked in a hot dry shop and allowed drying time before relubing. When done the bushings looked like new, other than having a matte appearance typical of using brake cleaner. The motor still gets hot, but that is a common symptom, to the point that one technician in Italy offers stouter motor coils to help overcome this. A fine alignment can be done with the motor mounted, by loosening the motor housing bolts and slightly realigning the stack of motor parts for optimal free spinning. One can feel the difference when spinning the shaft by hand. Ideally this gets done under belt preload. This is where the “giraffe” plinth mentioned above is useful, one can reach in and adjust the motor stack while running under load.

By now one might get the idea that these are painstaking to set up.

Belts

This a perceived fraught issue with the Swiss Thorens models, TD 124, 134, 135 and 184. A few years after these turntables were designed and built, the company changed management and nationality. There are many belt vendors out there, including the current Thorens company, that claim to sell the correct belt made of original materials and to original specs, but not everyone is convinced; there are reports of them not working as well as NOS belts from the Swiss years of Thorens, including belts with 50 years of service behind them.

I first opted for a belt from a seller on eBay that had good feedback for his TD-124 belts, which are supposedly the same as the TD-135. That belt took a few days of running before the table would reach proper speed without drastic realignment of the eddy-current brake. The brake still needed adjustment. It measures to published spec, but elasticity also matters.

One thought is a longer belt, midway between spec length and worn out length. I also tried two mid-size belts, which i bought here.

Another point brought up is that a tired motor needing service may not be able to overcome the resistance of the newer belt. Kits are available to refresh the bearings and felt oil-retention washers on these motors, as well as the new coils mentioned above.

The differing opinions and results on belts from various users led me to experiment a bit. After spending time with various belts I’ve found that it doesn’t matter which belt is used if the motor is internally aligned while using whatever belt. If the motor is aligned with the tightest firmest belt, other lighter belts will tend to work well without requiring realignment.

Plinth

Belt/idler turntables are reported to improve when tightly coupled to a non-resonant vibe-absorptive plinth. Slate is the current favorite, but thin-lam ply is also popular because it can be veneered.

Using the downloadable manual from Vinyl Engine (joining up is necessary to have access to their downloads), I scaled a printable template for the first layer of the plinth I’ll make for it. It’s a pdf, prints to 4 pages at 100%, then trim and tape together so the measurements marked on it –that span across pages- are correct.

It’s not perfectly proportioned, taken from an old scan, but the indicated measurements are within a few percent. This also should work for the TD-134 and TD-184. Cut out of 5/8 or 3/4 ply this would make a good “giraffe” plinth for motor adjustment.

Download “135_template_printable.pdf” 135_template_printable.pdf – Downloaded 152 times – 115 KB

In the end I went with no plinth top at all for my TD-135. I found a stock of old very dense and heavy wood in my shop, no idea what it is, and made a simple box out of it. I then put a thick piece of MDF in the bottom, laminated from two 1/2″ pieces, then fitted tightly and fastened to the box walls. There is a hole in it for the wires to go through, it has no attached feet, sits on appliance dampers. The 135 base has a piece of automotive door-edge protector on each corner, and it sits on the box without being fastened down. The box is crudely made, but it works very well in practice.