I'm adding this post for the OP, as well as anybody whom might visit this thread seeking information at a later date.
It does look like the range of TT's and Drive Motor Designs for the TT's has become extensive since the idea of a Used Model extended into suggestions for a Vintage Model as well.
It is known that a Vintage Model with a certain level of attention given to the servicing of the designs incorporated critical parts, such as a Platter Bearing, Motor Bearing (Idler Drive) and the Electrics can produce a TT that is a worthy contender to a Modern Design / Produced TT costing much more.
Add to the attention to servicing, additional attention for the optimisation of the Speed Control and the Vintage Model will catapult itself even further toward being a worthy competitor. It does not take too much searching to discover ancillaries are being offered and readily available, as 'Off the Shelf' or 'DIY Build', that have the capability to substantially improve on this area of performance as well.
Both Belt, or Idler Drives are easily improved on with this approach to additional ancillaries to control speed. I have a Custom Built Speed Control Unit that works on both Idler and Belt Drive TT's. It has proved a substantial improvement on my Idler Drives. I have not experienced it on an owned Belt Drive, but have heard another version of it used on a Belt Drive in another system and am of the opinion, the TT was much improved as a result of the ancillary being added.
The DD TT in general is already supplied with a design that will offer a very accurate speed control incorporated.
The add on ancillaries for a Belt or Idler Drive can in certain cases cost as much as a complete and functioning DD TT. This is one reason that attracts one to the DD TT as a worthwhile consideration.
DD TT's come with a more difficult task requirement, if there is a intention to improve on the Models designed Speed Control. A certain skill level is required to understand the Model of DD TT's electronics and it is best practice to use an EE with a known history of working on these designs, the chances are going to be significantly increased to receive a optimised end product.
My SP10 Mkii has a undergone a Overhaul of Electrics and Mechanical Parts. Additionally it has a Modification carried out by a very well respect EE who specialises in these TT's. The Mod' in place has improved Speed Control on this TT when compared to the usual function.
Many Vintage TT's in use are not optimised for use. This is ultimately present as a , result of the age of the TT Model.
The risk areas relate to the Platter Bearing, especially the unknown quantity of Rotations having happened and the condition within the Bearing Housing potentially being unwanted, whilst these rotations have been and are happening.
The Platter Bearing is an important consideration, the common encounter, when being investigative of the inner of the Bearing Housing. Is the chance that the Bearing Housing Internal and Parts that have a Mechanical Interface are Arid Dry.
Commonly the evidence to be seen, is that the Bearing Liner Bush, which will usually be produced from a Metal, is in direct contact with the Platter Spindle during rotations. Arid Dry Conditions with abrasive metal on metal operation is not optimised in any description.
A less common encounter is where the Spindle Base has a contact with a Steel Ball that has Scribe Marks etched into the Balls surface. The Arid Dry Condition with a Spindle seated upon and and in direct contact with a damaged ball, is certainly an unwanted interface. The abrasive effects of a defaced Ball will certainly have a unwanted impact on the quietness of the bearing in operation. Arid Dry Conditions with abrasive metal on metal operation is not optimised in any description.
The Thrust Pad in contact with the Ball, is most likely to be seen with a excessive wear, (indentation) this will increase friction, especially when the contact is Arid Dry. A worse case is when a evidence is witnessed, where the wear suggests that a Eccentric Rotation has been occurring, (this can suggest Bush Wear has occurred). The Worst case is to see evidence of Eccentric Rotation as the suggested cause of the Wear and Metal Powder (Probably Gold Colour) on the Thrust Pad (The Gold Dust is most likely dust from the Bush serving as a sacrificial part, and the dust is present as a result of abrasive contact in a Arid Dry interface.
There is today, no need to use Metal Bush Liners, there are Thermoplastics that are totally suitable for this role. Additionally there the same Thermoplastic Materials and other options, readily available to replace a Steel Ball and Thrust Pad.
The selection of replacement materials, will depend on how low the end user would like a 'coefficient of friction' to be achieved for the overall function and how fragile one would want their choice of materials to be, that are to be used within the bearing housing.
Changing the condition of Arid Dry and creating a Lubricated Bearing Internal, is quite straight forward, there are many different Viscosities for the Lubricant to consider. Where the complication arises is the maintaining the Lubrication within the Bearing Housing, as many designs as their basic are not able to keep a Lubricant, there is a leaching that will occur from the sump local to the Thrust Pad..
Maintaining Hydrodynamic Lubrication (HL) between the parts interfacing is another challenge and it is not known which Bearing Housing are able to maintain this condition from Vintage through to the Latest Designs.
The term (HL) is a Buzz Word for Bearing Design, but maintaining the condition throughout operation over a period is not easy to prove is in place, a alternative approach would be best to cultivate a periodical revisit to the needs for lubricant. .
Cultivating a discipline to care for the regular maintenance of checking Lubrication would be an advisable practice in this matter.
The overhauling a Bearing is getting more support daily, and there are skill sets making themselves available to assist with this task.
It is not uncommon for certain Brands Models to see direct swap out replacement Bearing Housings on offer. Built using Thermoplastics at the Metal Spindle Contact Interfaces, as well as having the option to select other materials as well.
A Bearing can also have Bespoke Bushes Machined to fit the radius dimension of the actual Spindle in use and the inner wall radius dimension of the Bearing Housing .
I have Bearing Housings using the above Swap Out Method and also have original Bearing Housings Overhauled and with New Parts Machined in Thermoplastic to suit the radius dimensions of the parts retained and supersede the use of original metal parts.
My experience is that it is quite possible and not too costly to achieve a Vintage TT, that can hold it own extremely closely to any TT up to 10 x it overall cost.
I have put my 'go to TT' along side TT's owned by others, to which one has the retail value of £25K, and have seen the responses from the attendees at the demonstrations. At a Public Demonstration, Two Directors of a Company that produces TT's to a value of £50K, told me they felt compelled to return to my Demonstration Room and give me a appraisal, which pretty much stated how impressed they were, and it reminded them of listening to their customers set ups with the most expensive systems.
SP10 Mkii's, most recently SP10 Mkii Kaneta and the SP10 R are now the main TT's within my HiFi Group. Prior to this the SME 20/12 with SME V was the Groups revered TT to aspire to.
The Groups SME owner has even moved on, originally to a Garrard 401 and now with a Scheu Analogue TT, that has undergone a few mod's and is reported by the HiFi Group as an extremely good TT and very affordable to achieve.
I have supplied a costing figure earlier that is realistic if the Donor TT is purchased with a prudent approach.
Note: This post is not to promote the SP10, it is to make it known, a Vintage TT of any Drive Type, will need to be thought about with a few extra considerations and associated costs, if wanting the chosen model to be optimised for function.