Vinyl Old timers: HK's and Rabco's

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.

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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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.

Sean,

You should follow this recent thread at AA for info on Rabcos, esp. Dave Shreve: http://www.audioasylum.com/audio/vinyl/messages/129076.html

Shreve is well-known for his modified Rabco SL-8E and his pioneering work on optimizing VTA/SRA.

Rabco marketed the expensive (active servo) SL-8E and cheaper turntable/arm ST-4 combo under their own name, and contributed the rotating tube/tire-rider arm design to the H/K turntables. In the H/K ST7 and ST8, the tubular arm is terminated at the rear with a tire that rides on the rear rotating tube. The arm moves laterally, "passively", to maintain even tire contact with the rotating tube. When the tire wears down or when the tube rotation drive becomes uneven, tangential tracking is compromised as angular errors become larger before the rear of the arm moves in reaction to stylus drag motion at the front.

THANK YOU for all of your help. I appreciate the quick responses and tips / tricks / links for further info.

As to Steve's description of how the tubular arm is driven, i'm sure that you did a bang-up job of describing it. However, i'm having a hard time understanding exactly what you mean. I'm sure that it would all fall into place once i could see a diagram or actual unit that was "gutted".

I will check the thread on AA and see if it answers my questions. Just in case though, i was curious as to whether or not the tubular Rabco arm could "easily" be installed onto another TT ??? Judging by Steve's description, it doesn't really sound like it. Sean
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