Project No. 13943; A TD124 done less reverently.
Above photo: August 2019. Chassis # 13943 sits on 4 inch thick slate. It sports a Graham 2.2 tonearm and a Shelter 501 type II moving coil cartridge. The original rubber platter mat has been removed and replaced by what is seen in the photo. No mushrooms in use. The dustcover is from Ferruccio in Switzerland. He calls it a "Hood". And I like it.
To begin with I need to state that the documentation of this project page differs from my other TD124 refurbish projects in that it does not include nearly as much photo documentation of the parts and assemblies and processes one goes through to refurbish one of these units. For that the reader may refer to any other project listed within the TD124 Dept index page. Instead, I am concentrating on and reporting the results achieved by the processes and different replacement parts that have been used here. Where necessary I do link to pages within this website that do photo document the processes. In that way it is presumed that the reader is already somewhat familiar with refurbishing a TD124.
I should also note that it will become evident over time that this is more than a single process being reported here. This is an extended report of this player over the span of many years. I plan to keep this one, while the other two TD124 players I have owned have been sold between the years 2016 and 2017. A time of economic necessities for this humble webmaster.
This chassis came to me with a worn and ragged external finish. A decision was made to chemically remove all coatings using a product called "Aircraft Remover". The name will be familiar to those who have worked with automotive finishes. Particularly those working in auto body shops and in auto body supply stores. Painters who work in the aviation field will also know it. After the beige enamel finish is removed we are left with the bare metal. This chassis is an aluminum die casting. There is evidence of some touch-up and surface prep work having been done at the foundry. Nothing ugly. For my part, and after having chemically stripped the paint from the aluminum, I found it necessary to go around the external surfaces with a 6 inch sanding board and 400 grit wet/dry sand paper. This was needed to smooth out some rather coarse grinding having been done long ago there at the foundry. Following the 400 grit I scuffed the outer surfaces with #000 steel wool, and then followed that with more scuffing using a 3M nylon scuff pad (green) to finish off the cleaning process.
Now I just have to decide what color to paint this unit. I do have some piano black acrylic lacquer that I am tempted to use. Perhaps a light medium blue, or I could just leave this one in bare aluminum. It kind of reminds me of vintage aircraft with aluminum skins. The practice with aircraft was to occasionally polish the aluminum, which was left bare to the elements....even at high altitudes. Ahh, the gold ol' days. But for now I'll leave it with a scuffed finish and occasionally apply that green nylon scuff pad to maintain the look.
Well, it's going to need a motor because the one that came with it was dead!
As providence sometimes will have it, (serendipity?) I had previously purchased one of those Papst Aussenlaufer motors. The one I bought was the 60 hz version for operation on the North American power grid.
re: The Papst motor. It had been Thorens practice to supply spare E50 motors to customers upon request. But then there came a time when the motor manufacturer was unable to produce any more without investing in new tooling. The old tooling had worn out. So Thorens Export Company, (that part of the company not in Lahr, West Germany but still located in Switzerland), chose to look for an alternate motor to offer its customers as a replacement. Long story short, they turned to Papst.
Here is a short summary of my time with the Papst;
It needs to be mentioned up front that the Papst motor of which I speak is as 3-phase design that -in order to function within a TD124 as a drop in replacement- must operate on single phase power. Yup, that's right; now we gotta make a three-phase motor run on single phase power. For that it takes a circuitry modification as described in service bulletin No. 22. (It's a hack!) I tried it this way for a month. For a month I experimented using this Papst motor (60 hz version) on 13943. Toward the end of that month I came to the conclusion that with the stupid hack and all this motor does have some potential with the TD124. Once up to speed, sound quality seemed just as good as with the E50. However it was not lost on me that without a dedicated 3-phase power supply to feed it the kind of power it was designed for, the motor was no where near to achieving its design potential. And....it is not within me to design and build power supply circuitry. That's just not in my wheelhouse. So I sold the Papst to an Electronics Engineer that wanted to tinker with it and ultimately to produce a dedicated 3-phase power supply for it.
With it gone, I Then put my focus back on getting an E50 to work its best. The motor that came with this chassis arrived dead. An analysis of the wiring suggested the coils had an internal short and I was now looking for a new coil replacement set. However I also had another motor from one of my other TD124 players (sn#7888) ready to drop in. But that motor required service as do all of these motors when they have been left in long term storage. At the least they get a thorough cleaning and re-lube. However there was another option....why not try one of Audiosilente's replacement and upgraded stator coil sets on this motor. Little did I know then that I was about to purchase more than one of these upgraded coil sets. They turned out to be good.
It has been known for some time that the E50 motor did evolve during the production run of the TD124. Forensic evidence suggests that it was sometime late in the run of the original version that Thorens became aware that not all was perfect with the E50. The early motors might tend to run a bit warm and - over the years - perhaps "cook" the insulator over the copper windings. An undocumented revision was made late in the first version and used thereafter One source suggests that the changes were made around SN# 40000.* And the mkII production run certainly includes this revision.
*Simone Lucchetti http://www.audiosilente.com/ (text is in Italian. Use translator to view in English)
The result of the coil revision was an apparently cooler running motor (to the touch) and one that seemed a bit more energetic. The revised E50 will reach operating speed quicker on a cold start and then run with more torque throughout the day. What's not to like! As it turns out the above link (audiosilente.com) does produce, and make available, an upgraded windings set for the E50 that is to the same spec as the motor windings used on the MKII models. These can be installed into any E50. The price was agreeable for me, so I ordered one set of coils to be used on 13943.
Delivery from Italy took exactly two weeks. Simone sent the coils via registered mail. He also attached an installation instruction in pdf format to an email to me. The instructions are in English as well as Italian, complete and easy to follow.
Here's a copy: coils installation pdf
side by side. old (left) new (right). The new coils from Simone are slightly larger and fit a bit tighter inside the core. And that's a good thing. We don't want the windings flopping about loosely within that case work while the motor runs under load. We want the windings to be constrained almost firm within the inner dimensions of the core. And these new coils do just that.
The windings offer operation at 3 different voltages, just like the original. The only real difference is that the magnet wire in these new windings is a slightly larger gage. I did not measure this since it would require surgery. Rather, I followed Simone's instruction sheet, soldered the new windings to the Thorens AC terminal and then went through the usual motor-rotor alignment process while the refurbished motor ran under its own power. As I type this 13943 is playing an Lp. Paul Simon, There Goes Rhymin' Simon. This is one of several albums I use for setting up. I will observe the operation of the player with new coils over the next couple of days then write down any observations I have to this page.
5/1/2014....I've had a couple of days to listen to 13943 using the new motor windings. Here are some observations about the operation and sound quality of the deck...
5/6/2014.....its been 6 days since my last notes. There are some changes.
Listening. Sound Quality is getting better in several ways. Mostly it is a more solid and steady sense of pace. Really good pace. Keep in mind that I have an SP10 mkII standing next to the Thorens. The SP10 provides a very strong reference when it comes to holding a steady pace. And the TD124, with the new coils from Simone, is moving closer into SP10 territory on this one aspect. Oh, lest I forget, this is operating better and sounding better than how I had it using the Papst motor in all categories of performance. To get the Papst working correctly, methinks a 3-phase power supply is required. What was Thorens thinking about with that hacked Papst motor anyway?!! It seems like a cheap hack to me. It would have been better had Thorens offered a service that supplied rebuilt E50 motors with new coils. You know, send in your old motor as core and receive a freshly refurbished unit, like automotive alternators, etc.
With the upgraded E50 There is a greater "jump factor" than before. Instruments and notes tend to pop out of the speakers immediately in front of me. Where before and by comparison it was a bit less energetic this way. The music tends to seem more palpable and in front of me. Closer to touching me from where I sit or stand. Did I just get a glimpse into the recording space? It does seem to be getting closer to that goal.
Quietness. This TD124, (and using the motor out of 7888) with its mkII conversion motor mountings installed, and with the new coils, is as quiet as they come. A really good sense of silence between the notes. During the blank space between tracks. Lead-in grooves, etc. Detail delivery. Inner details, the quieter ones, are now in crisper articulation than before. It delivers both the big energetic parts as well as the delicate softer bits with equality. I've heard this before with 2729 but now, with the new motor coils installed and working in, I'm getting more and better. Crisper. Sharper. Yet organic in overall character.
When it comes to signal versus noise it seems to be working into belt drive territory. In ways I can still remember it plays with a greater sense of quietness (in the parts where it is suppose to be) than I got from my old Teres 145. In this sense the player delivers on its original design promise.... to be an idler driven turntable that does not suffer from what reputably plagues almost all other idler drives.....rumble.
The sound field is as wide and open as I've heard any of my TD124 motor units deliver. It plays big but now with a better sense of articulation, pounce and pop.
Time for review. Lets consider what work the drive train has had done, and what I might yet do with its various components.
Upper platter and clutch: This component is at once a weakness and a strength of the TD124. The clutch operation is a very nice utility that one gets used to quickly and will be missed when operating other players. By moving the clutch lever the upper platter is lifted up from the lower spinning flywheel and held stationary while records are changed. This can also be used for instant cueing such as is employed in a broadcast environment. ..
But the thin upper aluminum shell of a platter quite often comes to us having been bent in a previous life. And just a small injury to this fragile and soft aluminum shell can ruin its function. Yes, fortunately the light upper shell can be straightened into a condition where the clutch parts won't rub against the spinning shell during play, but.... But that is just generally how these units tend to be found. In this instance I am using the upper platter that came to me on SN#2729, my first TD124 that came with a severely bent upper platter. I have been able to straighten this shell into a condition where there is no rubbing against the clutch lever and it lies flatly over the friction pucks on the iron flywheel. Functionally I have 100% utility of it. Visually, as the platter spins you can see evidence of a less than straight platter...but one that does not intrude upon the audible performance of this unit. And this upper platter is one of the early units manufactured by the spinning process. Later upper platters were produce by the more common stamping method. I'm not convinced one method of mfr is superior to the other, but the early one works fine for me now.
The Iron Flywheel: As it is: It is well machined in that all surfaces spin true and concentric. When this flywheel is mounted over the bearing, there is no need for concentric adjustments. Manufacturing tolerances were held quite closely and the concentric surfaces will spin well within .001inches of -Total Indicator Reading- every time the platter is mounted to its bearing.
There is the perceived issue of the iron metal below and the stronger magnets used in moving coil phono cartridges above. Consider that just beneath the cartridge, as it tracks the record groove, just beneath by less than 3/8 inches lies that iron. And the cartridge magnet does pull itself down toward the iron. This is something easily measured. In the case of a Denon DL-103R cartridge I frequently use on it, there is approximately 1/2 gram of pull being exerted between the cartridge magnet and this iron flywheel. Of course I compensate for it by using an electronic vtf gage that reports its down-force while holding the stylus at record level and directly over the iron flywheel. Then, when measuring vtf using the same gage while holding the stylus off to the side of the platter and away from the magnetic pull, the reading is 1/2 gram lighter. I find this situation livable.
Although, a non-magnetic platter of similar density to that of the iron seems like an attractive idea. Yet such ideas cost real money to realize and there is some anecdotal evidence out around the web to suggest that not everyone has had good experiences spending good money after less than perfectly manufactured 21'st century product. The original parts, when found in proper condition, are well worth holding onto. Should I venture into this territory, I'll report my experiences. And, by the way, it is within my wheelhouse to accurately measure and evaluate machined products.
Platter mats: Is there anything better than the original Thorens rubber mat? Of course there is.
When experimenting with platter mats on the TD124 upper platter, the 'fly in the ointment' is that 45 rpm adapter that pops upward out of mat center. A platter mat needs to fit the fixture that holds the adapter, or you just cover the adapter with any mat with a spindle sized hole in its center. Who plays 7-inch 45's these days anyway? Well I do have a couple of ideas for a 45 adapter replacement that holds a mat down. One can be seen here in a review of the Woodsong Audio Upper Platter Mat adapter..... and also there is a mod you can do the the oem 45 adapter. But those are the adapters and lets move on the the actual platter mats. Anyway I have some alternate platter-mat ideas currently in use. Will I share these with all readers? Well one of them might become a product and I'd like to be able to at least introduce the mat before anyone copies it. But yes, I have a platter mat that works way better than the oem rubber mat.
The original nylon platter bearing sleeves have been replaced with new Oilite bronze. The platter bearing shaft itself was carefully examined for evidence of wear. Using a micrometer, the shaft was measured for evidence of out-of-roundness and of taper. In both cases it turned out that there was no measurable evidence for either. However there was some visual indication of where the bushing sleeves and shaft had been running against one another. A very fine-grit strip of Crokus cloth (a rubberized abrasive) was used to put a new pollish all over the 50 year old bearing shaft. Once done, the shaft was measured once again with the micrometer and found to be still uniformly round, straight and the same original diameter (out to 4 decimal places). In this condition it was ready for the next 50 years.
The bearing ball at the tip of the shaft was also removed (unclipped) and examined for evidence of wear. This, like the shaft, showed no measurable evidence of wear. It was cleaned and placed back into its countersunk socket at the tip end of the shaft (with a dab of lube) and retained by a bronze clip retainer, which snaps into place.
The bottom thrust cap, attached to the bottom of the bearing housing by three machine bolts, has been upgraded with one of my gunmetal bronze caps. This very solid end plate provides a rigid, non flexing point for the bearing thrust. Currently I'm using a Teflon-infused Delrin thrust pad in place of the original Nylatron one that Thorens provided. According the material specification, it has 15% teflon mixed in with the Delrin. Wear rates with this material appear to be better than I've noticed when using plain Delrin or Nylatron as a thrust pad.*
* I've had approximately twelve years to experiment with different bearing thrust pad materials and observe wear rates.
I still use the same type of oil that Thorens recommended in the main bearing. A straight 20wt. turbine oil. But a modern equivalent and from the same oil company that provided the original. (Texaco)
Update circa August 2019. It was prior to my move away from the Seattle area that I lathe turned some Delrin bushing sleeves for this platter bearing. I wanted to experiment with alternate bushing materials and Delrin was at the top of my list of materials to try. One reason for this choice is that Delrin has a long history of success in applications like bushings and bearings as well as in higher impact applications for automotive uses. The material is naturally slippery, it holds up very well against heavy loads and is known to wear well. That was the fall of 2016. I did find it necessary to use a specialized kind of hone (not the abrasive type) to adjust size after pressing these new bushings in. After honing I had a running clearance comparable to what I'd seen with the sintered porous bronze Oilite bushings I'd been pressing in. With the Delrin bushings I have a running clearance of .001 bushing to shaft. That was my target operating clearance and it was realized after the hone operation. For lube I continued using the straight 20wt Texaco R&O 46 turbine oil that I have a stash of. What I noticed right away was that spin-down times increased dramatically in comparison to the Oilite bushings I'd been using. Since then I have removed the bearing shaft to check for evidence of wear periodically and found no evidence of concern. The lube is staying in the housing. Almost three years later I continue to observe how well these Delrin bushings are holding up....and they are. The one consideration here is that these bushings are not of the self-lube type and do require that the operator maintain necessary lube levels within the bearing housing! I keep the lube level all the way up to the top within the housing for apparent reasons here.
Discussed above. Having tried a Papst Aussenlaufer* motor, with some slight disappointment, I moved on to an E50, -- renewed not only with new rotor bushings and thrust pad, but also with new upgraded mk2 coils from Simone Lucchetti of Audiosilente. See notes above for how well this worked. Based on my experience so far I'll likely stay with the E50 described below.
* I know of one individual who is currently designing and building a dedicated 3-phase controller for the Papst Aussenlaufer. In fact, this individual has the exact same motor I fooled about with. I will report his results as he lets me know them. I do expect to hear of results far better than what I experienced while using this 3-phase motor on single phase power per the Thorens bulletin No. 22 hack. The bulletin 22 method employed a modified circuit to fake the three-phase motor into working on single-phase. (timing capacitors) My spidey sense says no way a motor hooked up like that can run as smoothly as it should. We think the dedicated 3-phase Power Supply will take a TD124 to new heights using the Papst Aussenlaufer. (hmmm, it wasn't then and isn't now in my budget -or- wheelhouse to get into 3-phase motor controllers)
Motor Controller for the E50 on single phase: There is likely something I can look at. For now let us save it for future reference. File under; "Yet to be tried". As far as I know, no one is actively offering a standalone motor controller specific to the needs of the E50 Thorens motor. Although there was one produced by Loricraft for use on their Garrard 301, 401 and Loricraft 501 players. I've yet to hear of anyone using one of these on a TD124, but the motors are of the same essential design but with differences in external case work and also wattage.
Motor Notes Update (8/8/2019): The E50 motor I have written about above , originally taken from 7888, was pulled out of 13943 and placed back into 7888. Then 7888 was sold with a healthy motor, (and healthy everything else). The reason for that was that the other E50 that 13943 originally came with was in need of new coils, or otherwise dead. Circa 2016, after selling 7888 with the above motor installed, I ordered another upgraded coil set from Audiosilente for this motor. That refurbish process went as above described except that I re-considered replacing the sintered bushings with new tighter fitting bushings as I had been doing up until this motor. After taking bushing and shaft measurements to analyze wear I concluded that by re-using the original motor bushings I would have .0008" to .0010 running clearance shaft to bushings. Fresh bushings would result in a lesser running clearance in the .0006 - .0008" range. So why not allow a couple of 'tenths' more clearance! So I kept that new pair of bushings in their little plastic bag and went with the older bushings, thoroughly cleaned and well soaked in fresh 20 wt turbine oil. There was a different result in fresh motor behavior after this motor refurbish with the looser fit - bushing to shaft. A slight difference. As before the motor came up to speed from a cold start within one rev. And that is from a cold start. The difference was in watching the strobe to determine speed pitch and watch it change as the deck warms up. Instead of slightly slowing after that initial coming up to speed -- as before, this unit wants to go ever-so-slightly faster than nominal for a few minutes then slows back down to the nominal 33-1/3rd. Just that little bit of extra clearance! Well that was 2016. Now it is 2019 and the motor still behaves that way. And I have a new replacement set of motor bushings that I think I'll just keep in their package and save for a different motor.
Another difference with this current motor and the first one is that it is in the mk1 motor grommet configuration (shorter post / single grommet). And in place of the generic rubber grommets I'm using Silicon motor grommets from Gel-Tech. More about those down below in the idler wheel notes. Anyway this motor is getting along fine.
I've tried several different belts. I have some notes on this elsewhere on the site. After some experimentation with new OEM Thorens (with logo) belts*, and with a few different aftermarket belts available cheaply on Ebay, I've settled, for now, with a belt supplied by Schopper. The Schopper belt duplicates the length, width, thickness while elasticity is slightly tighter than the oem Logo belt, but with a more modern compound material that sheds far less material residue onto the drive and driven pulley surfaces. Further, the Schopper belt does stretch just a bit after the first few weeks. And, in NA we use the smaller motor pulley for 60hz operation. Likely the same belt would seem too tight on the larger 50hz pulley.
Other individuals have noted that on certain stepped pulleys, particularly the last version as seen on the MkII players, belt tension can have a direct effect on noise levels at the stepped pulley. Of course this ties in with the amount of eddy brake influence. Use more eddy brake and the stepped pulley seems to generate more noise. Use a tighter fitting belt and then the stepped pulley seems to generate more noise. I've had two mkII players in for service and I did observe that there is a slightly greater amount of noise being generated at the stepped pulley in comparison to the earlier design. However this noise is ambient and airborne in nature and not necessarily surface borne and traveling through the chassis structure, which would be a greater concern. But it is of concern. Experiment with different belts to arrive at the best compromise with regard to ambient noise levels coming from the stepped pulley region of the chassis.
If I were to take the best design features of the entire production run of the TD124, my optimal TD124 would have the first version stepped pulley design, while using the later motor revision.
*available at your local Thorens Dealer
Thorens changed the stepped pulley bearing design three times over the production run of the TD124. The stepped pulley design on 13943 is the first version. It has a precision ground solid steel post anchored to the chassis from below by two set screws. The stepped pulley, containing sleeve bushings (bronze) and a spherical cup at the very top of its housing to hold a bearing ball (Ø 4mm). The stepped pulley with its bronze sleeve bushings, and bearing ball within, slides over the upright post. Gravity holds the stepped pulley over the post and against the bearing ball perched at the very top of the upright post to provide a vertical thrust point. For lubrication, the TD124 service manual is followed and straight 20wt turbine oil is applied liberally to the the bushing and shaft. It should be noted that within the bushing is a groove, centrally located, that holds a felt oil retainer. It is made certain that this felt is thoroughly saturated in the above noted lube.
The stepped pulley receives its drive from the motor-driven belt at the large ring on the very bottom. Above the belt ring are 4 stepped ring registers of different diameters to provide platter speeds from 78 to 16 rpm. The rubber tire of the idler wheel drives against one of these while being slightly pinched against the inner rim of the iron platter. This is how the platter is propelled. The stepped pulley might also be termed as a capstan. Like a pinch roller, but with 4 different rings for 4 different speeds.
The question becomes one of what can be done to maintain design integrity of this part of the drive train. My experience so far is that this earliest design of stepped pulley does not provide any significant problem to be overcome. The examples that have come across my workbench have not shown evidence of significant wear on either upright post or inside the bronze bushing sleeves. And the ring registers that drive the idler tire seem to have held up very well.
The 4mm bearing ball at the top can be replaced with a new one. But close examination by measure (micrometer) and by magnified vision (10x Loupe) have not shown any significant evidence of wear to these original parts. So I've only had to clean, re-lube and re-assemble the stepped pulleys that I've seen so far. I have experimented with using different bearing ball materials on this assembly. For instance I have used Silicon Ceramic bearing balls (gr 5) in place of the original hardened steel one. I can't say that I have heard, or measured, any significant difference between oem and any other bearing ball here.
This stepped pulley is of considerable import to the overall noisiness of this drive train. Using a mechanics stethoscope it is easy to point a finger at this area of the chassis as having the highest noise levels during operation. It is like the nexus of drive train vibes. Anything done that reduces noise here, has to be beneficial to the Signal/Noise Ratio of any TD124.
At this point I've tried three different kinds of idler wheels. 1) OEM, 2) two different reproductions of the oem and 3) one O-ring idler wheel from Audiosilente.
Firstly there are the original 50 year old ones found on the Thorens motor units as they come to me. In some cases I've seen these with the rubber showing cracked surfaces and a hardened surface all over the rubber. Others, however have appeared to me with still soft rubber, no cracking or crazing and no evidence (visual or audible) of any flat-spotting out on the rim where the rubber drives against the platter and stepped pulley rings.
It is possible to have an existing idler wheel re-covered in new rubber by one company that specializes in doing just that. http://www.terrysrubberrollers.com If you go this route you replace the tire rubber but retain the original steel parts of the wheel and also the bronze bushing sleeves within. And they may or may not have some wear in them. It's a viable and least expensive repair I can think of. By the way I have worked with one refurbished idler wheel done by this firm. It was on TD124 sn# 59805 which is photo documented for refurbish here and can be found back at the TD124 Dept index page. Terry's work did the trick and played a significant role in the process that restored new performance to that machine.
edit 8/8/2019 There used to be the option of buying from Mirko at "classicturntables.com" a new replacement idler wheel lathe-turned from bronze and with new bronze sleeve bushings, then fitted with the outer tire rubber. The Mirko idler wheel duplicated the shape and dimension of the oem Thorens idler wheel. Although he may have used a slightly different rubber compound than the original units. (likely it is a softer rubber) However that option no longer exists. Mirko does not answers emails and his site isn't working. Those wheels are still out there in service and, should rubber renewal be required, I'm confident Terry's Rubber Rollers can renew that good as new.
Schopper in Switzerland offers for sale a reproduction of the oem idler wheel. I have seen one of these up close and was impressed with the quality of workmanship. I was also impressed with how true all of its surfaces were when observed in operation. Not just the outside diameter but all surfaces spun concentric. (you can't say that about even oem wheels) The one I observed came to me with a "Idler Wheel Noise Reduction Kit", which included a small semi-clear plastic "container' with special thrust pad and a tiny bottle of lube.(ordered separately) In function this kit provided a sealed tub with lube in it to keep the idler thrust wet with lube at all times. The price was impressive but not out of reach. These can be purchased directly from Schopper at: http://www.schopper.ch/
A third option can be seen here: http://www.theanalogdept.com/o-ring_wheel.htm From Audiosilente (Italy) is a solid aluminum precision lathe-turned O-ring idler wheel that I have in this TD124 unit (13943) as I type this. It has been in use for a few years so I can report its performance over an extended period. You have to be careful when mounting the different O-rings to the wheel. It must bed perfectly into the wheel periphery groove so as not to go bump. It's not that hard to do, though. When I was still using the single rubber motor grommets and studs it did seem as though the drive noise level went upward in comparison to a well worn oem wheel I'd just taken off. But then I changed the motor grommets (std rubber fresh and firm) with Silicone grommets from Gel-Tech in Japan and drive train vibes dropped down into quiet territory. No measurements taken. Just listening.
Idler Wheel thrust washer.
This is the tiny little nylon flat washer ring that slips tightly over the upright precision ground steel post. This post serves as the axis of the idler wheel rotation and foundation behind its driving force. But the post takes most of the force on the horizontal plane and that little nylon washer serves more like a positional reference and isn't taking any high vertical loading. Nonetheless it shouldn't be neglected. So far I find that it is normal to find original thrust washers in good usable condition. I know this because I look them over with magnification and sharp lighting. But this could also be a point worthy of experimentation. Upon assembly, I just make sure that there is ample lube on this location.
Of course we can pay attention to the Schopper "Idler Wheel Noise Reduction Kit" which supplies a puddle of lube to the thrust end of the wheel. There is some food for thought there.
What makes it work; It runs on AC current. Within the motor coils are several different windings designed to allow the motor to operate at different voltage ranges as follows: 100/120 , 125/150, 200/250. These different voltage ranges are user selectable by means of a commutator board with an insulated screw that is threaded into one of the three voltage taps desired.
The motor will operate on either 50hz or 60hz mains frequencies. 60hz will result in 17% faster motor rpm than 50hz. The speed difference is compensated for by using a two ended drive pulley where one end is a diameter appropriate for the one frequency and the other end for the other frequency.
It's terminal speed is determined by a combination of factors approximately as follows:
The shaded pole induction motor constantly attempts to synchronize into the mains frequency but does not -- due to slippage at the poles. The main benefit of this design is a smoother running motor due to the lack a cogging effect like that which plague's synchronous motors.
Another benefit of the shaded pole motor is that its slippage at the poles allow the use of an eddy current brake as a speed pitch adjustor.
Another major brand that uses this type of motor is Garrard in their 301 and 401 models.
I found some short calculations in Machinery's Handbook to determine motor rpm when the outer platter is rotating at 33-1/3rd rpm. I've put one to use below.
(platter rpm is 33-1/3rd.)
(a) to know step pulley rpm: 9.682dia x 33.333 / .470dia = 686.66 rpm
(b) to know motor shaft rpm: 2.755dia x .686.66rpm / 1.177dia = 1607.rpm
Unloaded and at 60hz 110/120 vac the motor has been measured at 1750 rpm
Using the above method to calculate motor rpm I can estimate that the loaded motor must rotate at 1607rpm to turn the platter at 33-1/3rd rpm. This indicates a ~1% drop in motor rpm when driving the platter at 33-1/3rd rpm.
Some observations. By changing the AC mains voltage coming into the motor, the rpm will either increase or decrease with voltage change. More volts = more rpm. Less volts = lesser rpm.
Using my Viz IsoTap Wp-27A variable output voltage isolator, I can either decrease or increase voltage to the motor in 5 volt increments. A 5 volt change to the operating turntable will result in a visible difference in speed as seen at the strobe window. Perhaps on the order of a 1% speed change. (rough visual estimate)
If a variable frequency power supply were employed. Motor speed could be regulated by altering mains frequency to attain the desired platter rpm. To date, it is unknown if anyone has produced such a power supply for the TD124.