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Vinyl Old timers: HK's and Rabco's

Need some help here. I have seen several old HK ( Harman Kardon ) TT's that had Rabco linear trackers on them. I always assumed that this was the Rabco 8 arm. I recently saw a Rabco 8 for sale on a website and it was completely different. The arms that i remembered looked like a regular linear tracking arm with a straight tube and a headshell. The 8 as displayed on this website looked like a much wider and flatter piece of metal i.e. almost like a piece of flat-stock.

If this really is a Rabco 8, what model arm is it that i recall as being stock on the old HK tables ? Sean
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sean
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ivanj
35 posts
 
The flat Rabco arm was the original. Then, HK came out with the ST7 and ST5(?) which were integrated linear tracking TTs that had a cult following, and actually sounded good comapred to a lot of what was out there. Bob Graham actually used one to do some comparison listening tests when he first brought out his arm - that was supposed to be marketed by McIntosh, but that's another story!
sean OP
6,231 posts
 
In case you wanted to see what i was talking about Detlof, here's a link to one on Ebay. I've since been able to find several others that look like this even though i've never seen one before. Kind of amazing to me as to how i could have missed this design all of these years.

Ivan, so what were the "tubular" models on the HK tables called ? Which one actually worked better, the tubular models or the "flat stock" models ? Sean
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http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=1358781471
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albertporter
4,949 posts
 
Ivanj is correct. The original Rabco SL 8 was constructed with a wide and flat head shell that formed the entire tonearm except for the block and bearing mechanism that it plugged into.

I owned and modified at least three of these, getting excellent performance for the early 1970's. I mounted the early model we are discussing on several turntables including Thorens, Luxman and Linn while I worked in retail audio.

If you buy one and need information, I remember quite a few tricks, including several ways to improve tracking, and a way to speed up the cue and lift.
sean OP
6,231 posts
 
Thanks for your offer Albert. I will surely keep that in mind as i am looking for a "vintage" type arm / table combo to compliment the rest of a like-minded system. I am still curious as to the differences in performance between the flat arm and the tubular arm that was used later on. I'd love to hear from anyone that has info on either of these. Sean
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albertporter
4,949 posts
 
Sean, One of the mods I did on the early flat tone arm Rabco's was to reduce flex in the giant head shell (arm).

Originally this design was way too flexible, having been formed from wafer thin aluminum sheet with the edges bent over to increase strength. Certainly it was lightweight, but provided less than a perfect platform to secure the cartridge.

Add to this, the counterbalance was large and heavy in order to accommodate (heavy) cartridges of that era. I had a machine shop mill the counterbalance where it's weight balanced against my reference cartridge when fitted very close to the bearing point. (Reducing the moment of inertia).

I substituted other materials for the flat aluminum sheet design with balsa wood, Oak, steel and Plexiglas. Each offering trade off performance over the stock material.

Today I would consider Carbon fiber or other modern lightweight, but stiff materials to substitute for the aluminum.

I never heard the tubular version of the Rabco, but would assume it would be superior in rigidity to the flat design.
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