Linear Tracker ...I was wondering

mijostyn - do you have any idea how many times you have used the word "Horizontal Mass" on this thread alone.

"I won't even look at an air bearing arm because of the problem of too much horizontal mass."

Then, why are you posting here still ? 

FYI ..............et al 

Cartridges mounted on an ET 2 do not see the Horizontal Mass due to the patented I Beam/Counterweight design. A vertical leaf (flat) spring isolates the counterweights from the air bearing spindle. If interested to learn, it makes more sense, I think,  for you to do some research, download the manual, and come back with any questions if you have any..

I have used 50 Sonus Blue Gold 50x10-6cm/Dyne on the ET 2
with no problems whatsoever.  

ct0517, raw BS I'm afraid. Just what is that horizontal bean going through the air bearing? A perfect vacuum? It may have less horizontal mass than other linear arms but there is still a marked discrepancy. It is IMHO the best design for an air bearing arm almost identical to the Walker. Wonder why they stopped making them? Anyway I am still of the opinion that the best way to do a linear tracker is by having the horizontal axis servo driven. The physics of the situation does not change just because you do not like it. It should be horizontal effective mass by the way. The horizontal and vertical masses are the same. The effective masses are much different.
Terry9, yes, look at a picture of the Walker. Look back behind the cartridge to the intersection of the arm to the horizontal beam, the part that goes through the air bearing. At the intersection there is a clamp that joins the two. If you loosen the nuts you can twist the arm adjusting the azimuth and move it forwards and back adjusting the overhang or lack of overhang as it were. It is $120,000 but the money was not the issue, it is the design. This could be done with a stand alone arm probably for not much more than an Air Line. ET was doing it but stopped. I am not a big Walker fan. You get virtually the same isolation and performance out of an SME 30/12 with the V12 arm as you would with the Walker for less than 1/2 the price with no noisy compressors and air rushing around all over.

@mijostn1  You really need to get your facts straight particularly if you are going to debate the ET II arm with ct0517.  Outside of the desigjner, Bruce Thigpen, Chris is probably one of the most knowledgable people on the planet when it comes to the ET.   Chris's experiments with the arm have led to improvements Bruce has actually incorporated into the arm. 
 
@jagjag  If you want to take a swing at a linear tracker, I'd go for a used ET II;  They don't come up real often but I've see a few between $700 and $1000.   Setup can be exacting but once dialed in it pretty much stays put.  Azimuth adjustment is very simple as is VTA.  Bruce still supports the arm so you can get any parts you need to repair or upgrade it. Bruce has great customer support.  He responds promptly to your email inquiries.  

Mijo, my air New Way air bearings and bushings are inaudible at a few inches (63psi). The Trans-Fi at lowest workable pressure (9 mm Hg) is inaudible at 6 inches, but I usually use 20 mm Hg, which is inaudible at 3 feet.

@mijostyn
As entertaining as I find your posts, for me to continue to share direct experience information on this public chat forum thread, with someone replying to my posts based on theories, and no direct experience. (that’d be u) You need to show me a desire to learn and in this case, the ability to think outside the box.

I recommended that you go to the Eminent Technology website, download the ET2 owners manual and breeze through it. That would get you to at least 1st base, and I bet you would learn a lot too. Another option is to go to Florida and see the tonearm in action directly at Bruce’ factory. No, Bruce did not stop making it as you say. He also supplies parts as needed. A tonearm, whose basic design has not changed since the 80’s and is still SOTA. Whats the word again, for audio products that last that long ?

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For the Op and readers of this thread
Here is a short video on the Sonus Blue Gold cartridge I referred to earlier - whose compliance is 50 x 10-6cm/Dyne, and is set at 1.24 gms VTF. Many feel only the stiffest of carts can work on a air bearing linear tracker. They haven’t used an ET 2.

The ET 2.0 HP in room 2 - Aluminum armwand and single leaf spring counterweight.

https://www.youtube.com/watch?v=Q-AqjI2B1uY

https://photos.app.goo.gl/CQdPMuBW1JFN7Npk9