Must be a RABCO arm, which Harmon Kardon used on their linear tracking turntables from the 1970's. Heard one years ago, well built and solid HK decks but cannot recall too much about the arm. Regards, Richard.
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Your friend indeed pulled out a Rabco. The one you describe is most likely the later model and was sold separately as the model SL8 E. It was powered by a dry cell battery, which would electrically cue the arm down to the LP and back up. There were two very fine "whisker" leads on either side of the arm, at the very rear. When the arm would go out of alignment (much beyond the required 90 degrees), a post brushing one of these whiskers would engage another small motor, and a bead chain drive would move the arm back into correct alignment. Proper adjustment of this arm was very difficult. Not only was it necessary to have everything extraordinarily clean for it to function properly, the hidden battery losing power could cause damage to the LP. I used one of these arms on my reference turntable for nearly two years, and have information as to mods, upgrade battery (faster response of cue and correction), and counterbalance and head shell corrections. The bad news is there are literally dozens of arms now that will out perform this unit. If you want to resurrect it for fun, I could possibly offer help.
Kudos to Albert. I'm kind of a "nostalgia" buff when it comes to older audio gear and do remember the basic arm design, i wasn't familiar with all of the info that you provided. Thanks for filling us in. I was told by others that had worked with that arm "way back when" that it was a good arm in its' day, but was EXTREMELY finicky and hard to keep running. Nonetheless, it might be fun to play with. I wouldn't start off with any of your valuable vinyl though : ) Sean
I had a Rabco arm mounted on a Sony belt drive table in the early 70's. It was outstanding when it worked properly. I can still remember the faint "whirring" sound when it made an alignment correction. After about 6 years, the arm would mysteriously raise in the middle of a track, sometimes as many as 3 or 4 times during one selection. I was told that the "contacts" had corroded. I traded it towards a $500 Yamaha direct drive unit at the dealer who first sold me the Rabco/Sony unit. The Rabco was much better than the Yamaha ...when it was working properly. Thanks for the trip down memory lane...
All of the other comments about the Rabco Arm..are true..It iis probably the....
SL-8 Rabco Arm.?..which I owned and used for several years..
It is a "bitch" to set up and to align cartridges with, but
we were willing to do that in those long ago days..But, if
you get this arm, it has a tendency to make a little "buzz"
as the servo engages to correct the arm geometry as it
traces the groove...that "buzz" sometimes would come through
the speakers as a little "zzz" "zzz" as the arm moved. It
was audible in quiet passages of music, but audible at other
times...Some arms were modified to eliminate that...M&K, I
believe, had one of the modifications available at the time
and arms which were sent to them for modification did not
buzz as they moved...Just a word of warning...Lots of fun
to set up if you enjoy this sort of thing, but patience is
required...Try to find the M&K Rabco if you can..There are
not many out there...the rest tend to buzz....