Harmon Kardon ST-7 with Rabco Tonearm

"These are some of the most sought after turntables from that mid-70's era!"  Really?  If I remember correctly (and please do correct me if not), that turntable has a built-on version of the Rabco SL tonearm, only instead of the motor-drive pulling a chain that propels the tonearm across the LP while maintaining tangency in the big Rabco, the tonearm on the ST8 is propelled by a rotating rubber tire riding on a metal bar.  The issue with that set-up was noise from the rubber tire transmitting to the rear pivot and hence out to the cartridge.  It's historically very interesting but not the greatest in terms of success in reaching its goal.

Most troublesome TT ever made .

Maybe that's why he gave it to me!

I never owned one, but a close friend did.....agreed with schubert (above).   The arm is a dog - don't think it was Rabco.

I have four...(2) ST5's and (2) ST7's.  Incredibly frustrating to set the arm up to ride the roller properly...but...once it all comes together, it's audio Nirvana.  I have had over 15 esoteric turntables, from B&O's tangential tracking tables (not so good) to eclectic pivoting tone-arm turntables on some of the best platters out there, and find the HK / Rabco combination to be one of the best sounding.  I don't hear any rumble (as stated by someone above) and have the equipment to play really loud - if I want. The soundstage and depth of field is quite remarkable.  I highly recommend these if you have patience (yes, a lot of that), dexterity and motivation to really get into a piece of gear that will reward you with a wonderful music experience.