With a number of specialist tonearm producers, the United States was a thriving market for turntables. Rabco, based in Maryland, was one of these companies, selling its complicated SL-8 and SL-8E tangential-tracking tonearms from the late 1960s onwards. Powered by two small electric motors, they amassed a small but devoted following, prompting the company to expand into turntable production. The ST-4 was the outcome, and the company’s success drew Sidney Harman, who dutifully decided to purchase it for Harman International Industries, Inc. Rabco had replaced it with the ST-6 and ST-8 turntables by the time the sale was completed, and subsequently modified them to produce the ST-7, which had recently commenced production. The sole indication of its parentage was the ‘RABCO’ legend on top of the arm bearing assembly, which was thereafter offered as a Harman/Kardon product. By 1975, the deck you see here was selling for about £200 in the US, Europe, and Japan, more than twice the price of a Linn LP12.
Jacob Rabinow (January 8, 1910 – September 11, 1999), an engineer and inventor with no fewer than 229 US patents in mechanical, optical, and electrical devices, designed the ST-7. He was born in Kharkiv, Ukraine, but later moved to China and then to the United States, where he earned a Master’s Degree in Electrical Engineering. He started his own company after working on defense programs at the US National Institute of Standards and Technology. Radinow is responsible for a number of firsts, including the first disc-shaped magnetic storage media for computers (1954), the first straight-line phonograph (1959), and the first self-regulating clock (1960). Rabco was founded in 1968 by him, but he left after selling it to Harman. He won a number of honors during this time and wrote a book called Inventing for Fun and Profit in 1989.
When you encounter an ST-7 in person, a few things stand out: it’s a stunningly attractive and simple design on the outside, with a striking ‘mid-century futurist’ aspect. There are no plastic pieces on the plinth, which is built of thin planes of brushed aluminium. Touch controls are featured on the deck, which were the stuff of sci-fi nightmares in the early 1970s. A recessed stroboscope carved into the underside of the 2.4kg aluminium platter aids the variable speed feature. It’s a beautifully lovely item with superb ergonomics compared to other Japanese designs of the time — indeed, it looks more like a ruggedized Bang and Olufsen than a standard American turntable. The parallel tracking arm is straightforward to use and has removable arm wands that make cartridge changeover a breeze. The overall build quality is excellent – but not flawless, as we will find. The deck is 157x419x413mm in size and weighs 10kg.
It’s a different tale on the inside. The design is based on a belt drive, but that’s where the simplicity ends. The tonearm is a complex piece of equipment, mounted on a two-axis gimbal mount with optical end-of-side sensing. The tracking shaft is propelled over the surface of the record by a belt that turns from the bottom of the inner platter – which is, of course, driven by the turntable’s motor by another rubber belt. A tracking roller is turned by the latter. The roller is tilted enough while the arm is at zero degrees to move the tonearm at the correct speed for traversing an LP – approximately 0.17 inches per minute.
The mechanism is simpler than early Rabco decks that employed electric motors, yet being significantly more sophisticated than a traditional turntable. It’s still a hassle to service, and many ST-7s have been discarded over the years due to a lack of knowledge about how to fix them. Of fact, the same critique can be levelled at many Japanese direct drive decks from this era, with the exception that the ST-7 is primarily a mechanical technical issue, rather than an electronic one.
The tonearm is effectively mechanically coupled to the brushless DC turntable drive motor, which is perhaps the design’s major drawback. The long drive belt to the tracking shaft pulley, which dutifully transfers vibrations down the tracking shaft with only the tracking roller as the last line of decoupling, is all that separates it, despite the fact that it is a pretty quiet object with sophisticated electronic speed control. This is a rubber component that, like a cassette deck pinch roller, degrades over time and with repeated use. In other words, the deck has a lot of potential to sound less than ideal as it ages. Of course, this can be fixed, but most non-mechanical users won’t be able to do so. Another disadvantage is that the plinth is entirely empty and composed of aluminium panels, which aren’t exactly the least resonant material available. As a result, numerous models have had dampening panels installed inside throughout the years.
In a world where published specs were everything in the 1970s, the ST-7’s motor unit performed admirably, but it paled in comparison to the inflow of high-end Japanese direct drives at the time. Wow and flutter were both listed at 0.04 percent, with rumble at a respectable -68dB. Its tonearm specifications, on the other hand, were more spectacular, with zero tracking error, vertical friction, and lateral friction. The effective mass was reported to be 6g, which was extremely low for the time period. The deck functioned flawlessly while tracking an Ortofon OM-10, which was designed specifically for this application.
It’s fascinating to learn about a well-kept, completely serviced ST-7. It’s someone’s image of the state-of-the-art in vinyl in 1975, and it’s actually rather good in a number of respects – though to say it’s flawless would be too nice. The result is a sound that is clear, smooth, and unflustered, with an even and balanced quality that resembles open reel in some ways. You can tell you’re listening to a deck with a tangential tracking tonearm because it sounds well seated, stable, and has an outstanding stereo soundstage that continues to wow you no matter what record you play.
Things aren’t quite as amazing in other areas. The bass is a tad warm and boomy — which some people might prefer – and the midband has a minor tone coloring. It’s not one of those turntables that transports you from one recording studio to the next as you go through your whole record collection.
The deck has its own sound, which is nice and warm but not neutral. The treble, on the other hand, is really satisfying; it’s clear and crisp, just like other turntables with superb parallel tracking arms, and there’s virtually no side distortion. The Rabco’s main flaws are its modest speed instability (which can only be heard if you’ve been listening to a good quartz-locked direct drive deck) and susceptibility to external vibrations. It should be placed far away from loudspeakers and on a flat surface.
The Harman/Kardon Rabco ST-7 is best described as “flawed genius.” In comparison to its competitors, it’s a little out there, employing a novel solution to a problem that many would argue is more of an academic than a practical one. It’s still a fantastic deck to own and use, and a terrific conversation starter among your hi-fi buddies. When it was new, it was dubious value for money, but currently they can be had for nearly nothing if they need rebuilding, or up to £1,000 for a mint example. Expect costs to climb as we move further away from the high days of the 1970s.
Anyone who believes they can ‘set up a turntable’ with a basic belt-drive like the Pioneer PL-12D might reconsider after seeing the number of parts, and indeed adjustments, within the ST-7. The plus is that any competent DIYer should be able to get one going, and there are plenty of decks that need to be sorted out for pennies on the market. As a result, if you come across a Rabco in the classifieds, take it as is and pay a cheap price unless it’s in perfect operating order. Decks in excellent condition are now commanding significant sums of money. There’s a lot of information about the ST-7 online, including a download of the original user manual, which goes into how to set it up and service it in great detail. It’s not rocket science, but it’s a bit fiddly.