Rabco SL-8E Tone Arm

Oldears, you can eliminate the servo noise by updating the servo! Its not hard...

The thing is, in reality the Rabco is a pivoted tonearm, not really a pure SL type, because it must pivot in order to activate its servo. Once this was pointed out to me, I lost my mojo for it. Never owned one.

Depending on how well the servo is set up, it really can be a linear tracker, much more so than any of the air bearing arms I've seen. This is because its lateral and vertical tracking mass is the same. On an air bearing, the cartridge cantilever flexes somewhat, which can result in the tracking error being higher than a radial tracking arm.

So the Rabco was actually capable of the lowest tracking errors of any arm made.

The original servo essentially did not work though- it has to be rebuilt if you want the thing to work.

Is having equal vertical and lateral mass a part of the definition of a linear tracking tonearm? I would not think so. I guess you meant that it is one of the best SLs you've used, because of the low lateral mass, as opposed to any air-bearing SL tonearm which will have a high lateral mass. I have seen the issue of lateral mass argued both ways, high is good; high is bad. I have no dog in that fight. I think high vs low has to do with whether you use a high or low compliance cartridge, but could be wrong.

But as I have pointed out other posts you can minimise cantliver flex in tangential air bearing arms by employing electromagnetic damping. I used a Shure V15Vmr on an ET2 for about 6 years and the cantilever is still as straight as a die. A small ( nickel size for you guys ) ring magnet under the beam accomplishes this.
Servos are like Digital, they are only a little bit out all of the time. Sitting in the listening chair, with a Goldmund Studio, watching the servo lights go on and off constantly with a $10k cartridge on the end is not my idea of relaxing to music.