Why Linear Tracking never took off?

Twl's comments are to the point. As someone who tried several of the linear tracking arms in the mid-1980's, I found them to be a mixed bag. Linear tracking arms are conceptually the "ideal" way to reproduce LP's, since the path of the tonearm/cartridge duplicates the tangential path of the recording lathe cutter head. There are a number of practical and engineering problems, however, in making a good linear tracking assembly that is affordable.

First, the tolerances neeeded to produce a high-quality, air-bearing linear arm are very tight, which means that the manufacturing costs are likely to be much higher than a conventional pivoted tonearm.

Second, if you were going to invest in a good quality, air-bearing linear tracking arm, you needed to have a really solid, stable turntable that would accept the tonearm/bearing assembly. There weren't a lot of TT choices in the early to mid-1980's that were suitable for use with air-bearing linear tracking arms.

Third, the air pump needed for an air-bearing assembly posed additional engineering challenges. The pump must be able to deliver a fairly high volume of air at a very constant pressure (fluctuations in air pressure could lead to jerky movement of the tonearm). Noise was almost always a problem with those pumps, so having them in the same room with your playback system wasn't a good option. The alternative was to place the pump in an adjoining room or closet, and then run a long tube from the pump to the tonearm assembly. Needless to say, this tended to exacerbate the WAF (wife acceptance factor).

Last, not all cartridges were well suited for use with linear tracking arms -- there were either mounting problems, or problems with excessive noise being transmitted from the tracking assembly to the cartridge. There could also be problems with the rather stiff phono wiring harness, which could cause drag as the linear arm moved across the surface of the record.

In short, there was great potential in linear tracking arms, but their cost and the "tweakiness", and the expense of a really good matching turntable was more than most people could afford. With better pivoted tonearms becoming available from 1990 on, air-bearing linear tracking arms became relegated to the very highend market.

One rationale for linear arms was to maintain perfect tangency to the groove, following the track of the cutting head across the lacquer. In comparison, pivoted arms are truly tangent at only certain radii on the record, and this can result in distortion.

Linear tracking arms are far from simple in operation. TWL mentioned air bearing versions with pumps, and there have been others with multiple rotating rods or servo motors to facilitate the arms' lateral mobility, especially as required to track off-center records.

So I assume affordable Linear Tracking models from the 80s, such as Technics SL-10,Yamaha px-2,etc,are good in "theory"...but bad in "practice?"...are there any affordable models that come to mind...maybe the revox b791?

The Revox TT is a pretty good one for their "genre" of TT, which is direct drive, and mediocre linear tracking. If you wanted a TT of this type, you should be aware that the direct drive types will impart a motor vibration into the platter(whether they claim it won't or not) and the linear arm of that type will not really be true linear, but instead, a "crawler", and will be loose enough to lose information at the arm bearing. For the money that you will pay for a Revox 791, or a B&O 9000, you could get a nice, belt-drive, pivot arm TT, that would walk all over the Revox in terms of performance.

Twl, are Regas, VPI HW-19 IV, & Sotas better than Revox B79x?