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Thursday, September 17, 2020

Rek O Kut Tips Redux

Rek O Kut L34 Rondine Jr. + S160 tonearm

Although not quite in the same league as the Garrard 301, 401 and Thorens TD124 + MKII, this classic American turntable marque has a steady stream of enthusiasts and followers.

I've learned a few more tricks to keep vibration and noise at bay since I uploaded Rek O Kut Tips in the early 2000s.

Old and New Rubber Grommets

Even if they all look alike, Lord rubber grommets have different weight capacities. Unfortunately, there are no tell-tale marks. I only learned about this because I asked one of the sellers.

ROK L34 motor

For the larger and heavier motor used in the L34/L37/B12, I recommend the rubber grommets sold by ebay seller 10stan.

Papst Aussenläufer used in the B12GH

The softer grommets sold by tdsbill provided much better vibration isolation from the smaller and lighter Papst Aussenläufer motor.

Under the chassis of a ROK B12GH

With proper rubber grommets installed, make sure the motor floats freely and is not jammed by untidy cable routing.

Talented machinists have been offering brand new idler wheels for Rek O Kut turntables in the $50 range. Since the bearings wear out, it might be more cost-effective to just get a brand new idler wheel from a reputable seller rather than getting your old idler wheel refurbished for $35-$40.

The performance of the idler wheel in the center is as good as a refurbished original wheel with a good bearing.

Karmadon idler wheel for Rek O Kut L34/L37/B12GH

However, this precision idler wheel by Serge of Karmadon was a significant improvement in noise and vibration reduction over the stock and aftermarket units in the preceding picture. A meticulously grounded rubber wheel of proper Durometer rating is bonded to a hub milled from solid brass fitted with a sintered bearing machined to tighter tolerances. The performance gain was at par with using Audio Silente idler wheels on my TD124!

1/4" ball bearing
steel vs. ceramic

There's a smoothness in the "feel" of turning the platter over a ceramic bearing even if I can't claim that I heard an improvement in sound. Some say the ceramic bearing can wear out the thrust pad, I haven’t noticed any wear on mine after almost 5 years. Use it at your own risk.

Rek O Kut B12GH + Grace G565G

Using the proper rubber grommets, routing the cables neatly, with a Karmadon idler wheel and a ceramic bearing, the only noise I could detect from the ROK B12GH was air-rush from the built-in cooling fins. However, I wasn't as successful in using it in a lightweight plinth like I was with the Garrard 401 and Thorens TD124.

Rek O Kut L34 Rondine Jr.
+
Denon DA305

Unlike its more sophisticatedly engineered contemporaries from Garrard and Thorens, these Rek O Kut idler-driven turntables really need the help of a massive plinth to absorb noise and vibration.

JE Labs ROK L34 + SME 3012 and Excel ES801
DIY Plinth
ca. early 2000s

Friday, July 7, 2023

Japanese Idler-Driven Turntable Part 4: Realistic Mark-7

Here's a tale of two idler-driven turntables of Japanese origin sold by Radio Shack in the late 50s. They share the same model badge and engineering features but they aren't exactly twins.🤔

This turntable/tonearm combination has been in my collection for over twenty years. I wired the tonearm for stereo because I particularly enjoy using it with the Shure M3D and M7D.

I couldn't find this in any of the Radio Shack Catalogs issued from the late 50s to the early 60s unless it escaped my tired, old eyes.

from page 2 of the 1957 Radio Shack Sale Flyer

However, the A-3 tonearm, which is essentially a Calrad SV12/Musicmaster Model 12/Velvet Touch sibling, was featured in the 1957 sale flyer above.

from page 4 of the 1958 Radio Shack Sale Flyer

This is the Mark 7 turntable recorded in the Radio Shack Catalog Vault.

Based on the shape of the chassis, this Mark 7 is perhaps the younger of the two since it looks very similar to the succeeding Mark 8, which I will discuss in a future installment.

DIFFERENCES

Although not quite as heavy and massive as a QRK or Russco, the cast aluminum chassis is very rigid on both units. The earlier MK7 chassis above is configured to accommodate a 9"-10" tonearm, while the later MK7 below was designed as a "motor unit" like the Garrard 301 and 401.

The speed selector linkage to the idler wheel in both are similar, but due to a slight difference in the motor mounting layout, the idler arm and idler wheels are not interchangeable.

SIMILARITIES

Except for the paint color, this hysteresis motor is exactly the same unit fitted to my NEAT P58H, which I covered in Part 2 of this series. Click here for motor servicing information.

The main bearing is an oil lubricated design, which supports a 3-lb. cast aluminum platter.

MODs & TIPs

Before moving on, the younger MK7 depicted above had a serious issue - the motor has a bent rotor spindle!😔 Will I be able to save it by adapting the motor from another Lafayette PK245 (don't ask my wife how many turntables I own 😆) with a warped platter?🤔

While planning the motor transplant, I examined the MK7 idler wheel condition and decided it might be worth rejuvenating.

So I mounted it on a handheld drill, deglazed the rolling surface with 400 grit sandpaper, and soaked it in brake fluid for over a week. This was suggested to me decades ago by a kind soul who visited the Rek-O-Kut Tips page in my old website. It has worked with two other Japanese idler wheels but I've never tried it on a Lenco or Rek O Kut. Back in those days, it was more convenient to just send Lenco and ROK wheels to Ed Crockett, RIP 😞 or Terry Witt 👍, who's still catering to the needs of audio DIYers.