Thorens TD125 Restoration

I purchased a Thorens TD125 at a yard sale a couple of months ago. It had been in disuse for many years. It was dirty, had some damage to the veneer, was missing a headshell, and was reported to "not work." After much internal debate ("Do I really need another turntable? Do I really need another project...") I paid the $20 asking price. Here's what I brought home:



A quick look confirmed what I had hoped... the unit "doesn't work" because there is no belt. The motor runs fine without any noise.

I disassembled the unit from the plinth and found various household items to support it. This is not easy. The turntable is heavy, and there are no good places to grab it to pick it up out of the plinth. It's unwieldy and difficult to find places to support it when out of the plinth. To get it out of the plinth, the bottom cover must be removed. Then there are two wood screws holding strain reliefs for the power and signal cables. Finally, there are four slotted hex head cap screws that go up from the bottom through mounting blocks on the plinth into the main turntable chassis.

Here's a view of one part of the table inverted and supported on some large empty yogurt containers. (I like Divotdog's "jig" better than mine, but I had to use what was on hand.)



To separate the fixed chassis from the sprung main chassis and armboard assembly, first the tonearm wiring has to be unmounted from the fixed chassis. There's a strain relief and two screws holding down the terminal strip. That's it. There's also an "L" shaped piece of metal that attaches along with the terminal strip. I don't know what the function of this piece is, but I took the above photo mostly so I'd know how that piece went back.

After the wiring is free the two chassis may be disconnected. There are three very small locknuts that hold the suspension bumper assemblies together adjacent to the large nylon suspension adjusters. Once the nuts, washers, and rubber bumpers are removed the fixed chassis just lifts off the springs that stay on the sprung chassis. Now it's time for more yogurt containers and another clear workspace for the fixed chassis.

More to come soon....

I have two lengths of 4X4 post I use to sit the table on to work on mine, just support the edges. For the cost of the proper head shell, I would look for a TP16 MkI tone arm with head shell included for just a bit more.
Regards,
Jim

Jon,
Ping me if you're looking for a factory plinth in decent shape. PM me and we can work out a deal if interested.

Damping the chassis:

My initial approach was going to be to simply restore the table to good operating and cosmetic condition without any modifications. I wanted to have a baseline impression of how the table as-designed performed. After disassembling the two chassis I decided that I really didn't want to go in there again so I elected to make one modification that I had read about on The Analog Department website. This modification involved applying vibration damping material to the underside of the cast aluminum chassis. Here's the "before" picture:



I purchased a package of "Evercoat Q-Pads Noise and Vibration Deadening Panels" from an auto body supply house. These are 12 inch squares of a heavy asphalt-like material, adhesive backed, about 1/8 thick. It comes six squares to a package for $30. The primary use is for deadening automotive panels - inside doors, floors, etc, but the package also shows using it at home on ventilation ductwork, washing machines, and even speaker boxes (!) The material is fairly easy to work with. It doesn't cut through with a razor blade easily, but I found that it could be broken cleanly and easily along a good deep score mark. Here's the first piece applied:



The material is too stiff to follow the deep contours of the casting. The Q-Pad instructions say that the stuff can be heated up to 300F to mold it to irregular surfaces. Seems awfully hot to me. I cut my pieces to size and then held them over the stove with a pair of pliers until they got kind of droopy. They did not have to get too hot to touch to be soft enough to mold around the contours you see in the pictures. The final result:



This was not hard work but it got to be very tedious after applying the bigger, more uniformly shaped pieces. After I finished I realized that there is probably no good reason to cut the material to fit between the ribs. That was how I had seen it done on theanalogdept.com site, so I blindly followed suit. If I were doing this again I'd make sure there's enough clearance (I'm pretty sure there is) and just cover the whole thing, ribs and all. Might have to heat the material a little hotter and more carefully to make such a tight bend, but I think it would make the job a lot faster and easier and it should even work better to damp out vibrations of the chassis.

Next up - The bumpers.

Wow, Thanks for the excellent pictures and explanation. That looks like something I will have to do to mine when I get to that step. It has not been taken apart to that level yet so when it does this thread will be my reference.

Thanks

Bill

Suspension Bumpers

The original rubber suspension bumpers had "perished," as our British friends like to say.



These bumpers only come into play when the table has been jarred with quite some force. Since they aren't touching anything when the table is actually playing (shouldn't be, anyway) I felt comfortable improvising replacement pieces. The originals seem to be quite soft, which I guess might reduce the "violence" when the suspension bottoms out, but I couldn't readily find any soft rubber pieces of the right general shape. A trip to Home Depot yielded some thin Neoprene washers, and I had some little plastic vacuum caps that I cut the ends off to make a short tube to slide over the central pin. My little tubes are slightly larger than necessary, but again - the suspension shouldn't be moving that far laterally while playing that the tubes would ever contact the very large mating clearance hole.

Here are the pieces:



I glued the neoprene to the original backing washers with Crazy Glue. This keeps the neoprene washers from falling onto the chassis and possibly causing a vibration. Here's the way they set up, shown without the chassis installed. The chassis sits between the upper and lower bumpers. Note that the backing washers have different size holes. The smaller hole washer goes on top (well, on bottom in the running position) and it sits on a shoulder on the pin. That's what sets the limits on the suspension travel.



Next up -- the electronics.

One thing before I get to the electronics... Some people recommend removing the small pieces of foam from the springs. They're intended to damp out spring vibration, but some people think they act to allow some undesirable coupling of the sprung and unsprung chassis. I chose to leave mine in. The foam is pretty soft, I cannot see it transmitting much of anything between the chassis. I think keeping the springs from ringing is more important. I could be wrong.

Electronics and 78 RPM.

The circuit board has a number of electrolytic capacitors that I thought I should replace. I ordered all the values I needed from Newark, and went up slightly in voltage. After I ordered them, I researched modifying the motor control to change the useless 16 2/3 RPM setting into a more useful 78 RPM setting. Turns out that one of those electrolytics needs to be a different value, along with changing the value of two of the film capacitors.

Here's the "before:"



And the "after:"



I hadn't bothered to check the dimensions of the replacement caps I ordered. I assumed (I know, I know....) that modern caps would always be smaller than the 40 year old caps on the board. Wrong. Sprague Atoms are big. It was a very tight squeeze but I got them in. Note that the topmost cap is nice and small. That's one for the 78RPM mod and I got it locally. It's a Nichicon, same rating as the long silver one at the bottom. It would have been easier if I had gotten smaller caps.

The Thorens instructions for adjusting the control board include using one of the trimpots to zero out the DC component of the signal. With the trimpot all the way over to one side I was still above the spec. Near as I can misunderstand the motor control circuit, there's an AC frequency that is synthesized by the control board. It's a kind of a push-pull circuit, and setting the DC offset to zero is really matching the amplitudes of the push side and pull side. (This is how I interpret it anyway. If I'm off base, someone please correct me so we don't let this misinformation stand.) With my knowledge that is barely sufficient to be dangerous, I looked at the circuit around the trim pot and decided that perhaps the small-signal transistors were no longer matched closely enough. Maybe they never were. The resistors I checked were all OK. One of the transistor P/Ns on the schematic was still available. The other was not, but Google found an obscure English web page that listed an equivalent number. I replaced the transistors and fixed the problem! (dumb luck). BTW, Thorens must have made a lot of running changes on these boards. When I removed the original transistors, they didn't match the numbers on the schematic. I couldn't find a cross reference for them, but I looked up the datasheets and saw that they were very similar to the units I had bought. There were also a few minor layout changes. The replacement transistors are all metal cans, I didn't take another pic.

Odds and Ends

Here's a picture of the other side of the stationary chassis. This side normally is hidden because the sprung chassis sits on top of it. Before I reassembled the two chassis together, I removed the nylon cups and cleaned them and the threads in the chassis. I put a tiny dab of teflon grease on the nylon before screwing them back in. There aren't many threads in the chassis, and it is easy to cross thread and screw up the nylon. I was very careful and had no problems. I also put a little of the teflon grease on the phenolic pads on the springs that sit inside the nylon cups. I wanted to be able to turn the adjusters without winding up the springs.



You can see the size of the clearance holes for the suspension limiting pins adjacent to the large white spring seat/adjuster cups. You can also see an outline of where the bumpers had contacted the chassis. Something I didn't notice until I went to put on a belt later on... The nylon pulley on the motor has been pushed way too far down on the shaft. I have no idea how that would have happened. I was able to pull it back into position and there was still plenty of friction to keep the pulley from spinning on the shaft. Also visible is a strip of foam on the strobe housing that has perished. I replaced the foam with some similar weatherstripping from Home Depot. I think the foam is another suspension bumper, or perhaps it is there to shield light from the strobe from leaking out and becoming visible where it isn't supposed to be. The housing is slid into the 50Hz position only so I could clean around it better. At the bottom of the picture you can see the angled mirror that is part of the strobe viewing system. Normally the brushed aluminum control panel sits along that front edge at the bottom of the picture. I had removed it so I could more easily clean everything. The mirror was all cloudy with nicotine (as was the rest of the table). I used alcohol to remove the haze from the optical parts. Not shown here is the thick rectangular window that sits above that mirror and is enclosed by the control panel. There's a black spring steel clip that holds it in place. The clip had started to rust just a tiny bit, and there was a little orange/brown spot visible through the strobe window that was annoying me, so I stripped and repainted the spring clip with some Krylon semi-flat black spray paint. (This was the same paint I used on the lower part of the plinth, more on that soon.)



When I went to put the clip and window back in place, I was amazed at how it nested right into some tabs and notches in the chassis. This whole unit is really a fine example of Swiss/German consumer product engineering. It is fairly complex with many individual pieces and fasteners, yet it disassembles and reassembles with ease. Most of the fasteners are captive, meaning that when you loosen them they remain with one of the components and don't just fall out of place. This really simplifies working on the unit, and is not the kind of attention to detail normally seen.

I didn't take any pictures of the two chassis joined back together.

Next up: The tonearm.

The Tonearm

The tonearm really looked crappy when I got the table. There were paint spatters and tape residue on it. No headshell, no bias weight, some corrosion on various parts, and the bias weight arm and string hanger were a little bent. The tonearm rest was broken. These arms have a soft rubber insert that decouples the counterweight from the arm tube. The rubber perishes (I'm loving that word) and the counterweight sags and takes a decidedly un-masculine posture. I didn't photograph mine, but here's a similar one I found on the web. Mine was much worse, perhaps the downward angle was twice as much. The one in the picture shows no rubber between the two parts of the coupler. There should be about 1/8" of rubber between the two, though that's actually an earlier tonearm. Maybe those were different.



I took apart the coupler and had to scrape away the remnants of the rubber. I bought some very soft natural latex tubing from McMaster Carr. It's slightly larger OD than the ID of the mating tube, and it's ID is slightly smaller than the sides of the square cross-section piece that fits inside. I've seen pictures of the original Thorens part, and it is contoured with "mushroom heads" where the rubber protrudes out either side of the tube. I also bought some O-rings about the size of the mushroom heads in case I wanted to more closely simulate the Thorens part.



I used a little silicone spray to help things along and I was able to stuff a piece of tubing through the metal housing. I cut it about 1/4" too long hoping that when I assembled it the compression of the extra length would form a mushroom head between the two pieces. It came out OK. It was hard to cut cleanly. I think if I had been able to make a more accurate and clean right angle cut I would have had a nearly perfect mushroom head.





I bought a spool of clear polyester thread and I found a brass nut that weighs 1.4 grams. I believe this is the specified weight for the anti-skating weight, but I'm not sure. It is the right weight for a similar but older tonearm that is a little shorter. It was a challenge to tie a bowline knot in that nearly invisible thread so I'd have a loop to go on the adjusting arm that wouldn't just close up like a noose. It was also a challenge to tie an appropriate knot around the nut. I cheated there and added a dab of Crazy Glue to keep it from untying.



Here are the pieces all assembled:



I had been looking for a headshell but they kept going for big bucks on ebay. I found this entire donor arm instead. Headshell, Shure M75 cartridge, armrest, and even a different arm should I want to try that at some point.



Unfortunately the armrest is a little different. Mine is a post that goes though a locking collar under the armboard for adjustable height. The one above just simply tightens down to the armboard at a fixed height. I'd have to add a washer to keep it from falling down through my armboard hole. I was able to remove the broken plastic piece from mine... it unscrews. The one on the donor board seems to have been molded in place on the metal. I can turn it but it does not unscrew. It just turns and turns (with difficulty) on the metal but it won't come off.

Next: The unveiling!

The Goods!

I neglected to discuss the plinth. I didn't take any pictures along the way, this is what I did:
I reglued the two pieces that were peeling off. I removed the rest of the strip that was missing a piece and replaced it with a new piece of teak veneer that I found. I used Rock Miracle to strip the original finish from the teak. This worked surprisingly well. I used some fine sandpaper and then 0000 steel wool to remove any remaining imperfections and smooth down the surface. I applied Watco Danish Oil - Natural - which left the teak quite a lot darker and browner in color than it had been. It looks more like walnut. It looks really good, but I would have preferred a lighter, more traditional "Danish" teak look. If anyone has suggestions for lightening it without too much work, I'm all ears. I also wouldn't mind giving it a little more of a rubbed luster. Would a paste wax work for that?

After I finished the teak, I masked off the entire plinth, inside and out, except for the black section at the bottom. I lightly sanded that, and used Krylon semi-flat black spray paint to refinish it. It came out fine, though there are some imperfections in the wood right at the edges that I didn't know how to fix. Not too noticeable.

Once more... the before:



And now:

A few more odds and ends.

The platter bearing was bone dry when I got it, but there seemed to be no damage. It spun freely even dry, no noise, no play. I cleaned it with alcohol and used a very lightweight oil I had obtained some time ago for another purpose. The platter spins with no noise or vibration and is difficult to remove because of the hydraulic suction. It does not spin down for nearly as long as others report, though. Spinning it by hand (belt off) to about 33 RPM, it comes to rest in only about a minute. Supposedly they can spin for four minutes when in good shape. I'll have to do a more serious cleaning and make sure that it is the right oil I have.

I also need a gram scale to calibrate the toneam VTF mechanism. It uses a spring and I suspect it is not set up right.

So far, though, with limited listening and with this Shure M75 conical stylus of unknown condition, and with unknown VTF it sounds terrific. Deep bass, really pronounced and warm midrange, maybe a little soft around the high edges. I am comparing it to a B&O with a new Soundsmith SMMC-2 cartridge, a setup I think is almost diametrically opposite to the Thorens/Shure. The contrast is quite apparent.

Beautiful! You should be proud of your work.

Thanks! It is gratifying when it comes together reasonably well. I wish I knew that the stylus was good and what the tracking force is... I'd like to play more than beater albums on it right now! Although... the beaters I've played so far have never sounded better.

Well done! :thmbsp: she looks good.

marc mc

That's excellent work there!

I loved those TTs back in the day!

I think your extensive work was well-justified by the results.

So gratifying to see a "Classic" given a second chance! :thmbsp:

bsujeep said:

Wow, Thanks for the excellent pictures and explanation. That looks like something I will have to do to mine when I get to that step. It has not been taken apart to that level yet so when it does this thread will be my reference.

Thanks

Bill

Click to expand...

Hi Bill,
Mel told me he was working with you on your TD125. I don't know if I can add anything to what Mel already knows, but feel free to ask. Someday soon I may want to pick Mel's brain about sand-filled plinths.

Looking good. Also I love them shures m75's Get a cheap 3rd party stylus and you are good to go.

JonL said:

Thanks! It is gratifying when it comes together reasonably well. I wish I knew that the stylus was good and what the tracking force is... I'd like to play more than beater albums on it right now! Although... the beaters I've played so far have never sounded better.

Click to expand...

What number does the stylus say? Its probably around 2 to 1.5 The best thing about those carts is you can get everything from 78 stylus to jico sas if you want. I use cheap Phasftil styluses and they work great.
The Shure M75 is about equal to the V15 II

Have you looked on Vinyl Engine for a manual?