Inasmuch as I love music and retrotech high fidelity music reproduction, I think it's healthy to take periodic breaks from hifi. Frequent visitors know that I also enjoy photography, especially using black and white film loaded in old school manual focus cameras.
So today's blog is about the Shoten R50 lens adapter that's designed to take a 50mm (Note: a 35mm, 45mm, 55mm or 58mm, etc. won't focus accurately) Pentax K bayonet mount lens and fully couple to the rangefinder focus cam of a Leica M body from 0.7 meters to infinity.
I bought this Lafayette PK300 idler-driven turntable because it looked like an improved Shield MO-19 (aka NEAT P58H) with the added feature of an eddy current pitch control as found in the Garrard 301/401 and Thorens TD124.
Shield MO-19 vs. Lafayette PK300
Comparing them side by side, the PK300 turned out to be proportionately smaller in all dimensions and lighter in weight. Hmmm🤔…let's travel back to the late 50s.
One morning, I discovered the right channel of my Ortofon STM-72 was dead. While waiting for the Weller WTCPS soldering station to heat up, I carefully peeled the foilcal to pull apart the 2-piece tubular housing so I can resolder the broken cable connection(s).
It was past lunch, so I took one last sweep at the Kutztown Spring 2021 radio meet before heading home. That's when I noticed this cabinet with a familiar looking metal-grilled driver partially hidden behind a huge pile of equipment. Without haggling, I handed a couple of ATM bills to the seller and we shook hands.
As soon as I got home I went through my Japanese audio magazine shelf and pulled this Stereo Sound Special Issue about Vintage Speaker Units, published in 2002.
Not exactly the General Electric A1-401 featured in the magazine but the slightly earlier A1-400. Pretty good memory for someone pushing 60, huh? 😉
GE A1-400 specs
As stated in the spec sheet, the perforated metal grill functions as a mechanical roll off filter for the 12" driver and the non-polarized wax and paper capacitor filters frequencies below 1800 Hz from reaching the 2 3/4" cone tweeter.
I also recognized this period correct DIY tuned pipe enclosure designed for corner placement. It was built based on an article published in the May 1955 issue of Audio (go to page 18), authored by Norman H. Bates.
BTW, AFAIK, he's not related to the lead character in Hitchcock's thriller. 🤣
Vocals are nicely rendered! The transition between the low and high frequency drivers is very coherent, as to be expected between two paper coned transducers. If I were forced to split hairs, I hear a tinge of nasal coloration in the lower region of male vocals, which I never notice with any of my Altec speakers.
Musical instruments and percussion are also well reproduced! Bass extension and definition of the A1-400 in the tuned pipe corner cabinet is at par with the Altec 756B in a 2.5 cf box, if not a couple of Hz more extended. Top end overtones are silky smooth and airy. Even if this cone tweeter lacks the ultimate transient speed and shimmer of a fine horn/compression driver combination, it's probably the finest I've ever heard!
I guesstimate its sensitivity to be in the high 90s/W/M because it'll boogie, driven by the 1250 mW SE triode connected 46 or 1500 mW SE10 amp. Although I can also listen to my Altec mini 757 with those aforementioned amps at respectable SPLs, it needs at least an SE2A3 for full dimensional monaural listening pleasure.
Kudos to Mr. Bates' corner loaded tuned pipe cabinet for the aforementioned impressive bass performance and my perceived easy-to-drive/high sensitivity nature of this speaker system. Kids, this enclosure was designed during the slide rule era!👍
Now I'm inspired to pursue my 285mW SE112A mono amp project.😊
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I really enjoy this speaker with a GE RPX or VRII phono cartridge tracing Atomic/Space Age/Exotica Lounge/Bachelor Pad mono LPs from the 50s by the likes of Martin Denny, Arthur Lyman, Walter Wanderley, etc.
After 21 years of hunting, I finally got a satisfying taste of the GE co-ax. I've seen this on eBay between $150-175, which I believe is a fair price for a unit with intact cones and no voice coil rubbing. A couple of my Instagram contacts even expressed fondness and admiration for this speaker when they saw a glimpse of it in my posts!
I now regret leaving my RCA 501-S1 in the attic 😔 because it would have made for a very interesting shootout. If I can trust my sonic memory though, the RCA didn't have the nasal coloration in the lower midrange I noted earlier. OTOH, the top end of the RCA could be deemed more reticent or refined depending on the listener's taste.
I debated whether to refinish the cabinet but the patina grew on me.😊
In the context of my monaural hi-fi system, it shall remain second only to the Altec mini 757 because when I played a young Sinatra LP for my buddy Ding, he initially thought it was Bing Crosby.😄 Sinatra only sounds like Sinatra LIVE or on an ALTEC!👍😎
Let's see what the gentlemen at Stereo Sound thought of its younger A1-401 brother two decades ago...
The scan below is from Stereo Sound Vintage Analog 2, 2014
Looking back to my late 90s home brewer article for Sound Practices issue 17, I noticed that a good number of components in my hifi system then are still serving two and a half decades later. The Tamura TKS83 moving coil step up transformer is one of them.
After building a hifi system for my cousin during lockdown, the Hashimoto HM7s made me realize that while the Tamura TKS83s can equal the HM7s in terms of bandwidth, the TKS83s can sound mechanical. It also became apparent that there are areas in which the classic Altec 4722s and 15095As can be improved upon.
When I finally heard a pair of Peerless 4629s, I was very impressed by their uncanny ability to reproduce very lifelike 3-dimensional vocals. However, I was quite disappointed when I played anything greater than a string or jazz quartet because the sound started getting mushy and dynamically compressed.
Overall, my ears still prefer the smaller and more affordable brother, the Altec 4722!
Upon our return from the expedition, a sumptuous dinner prepared by Tish + a bottle of Ripasso awaited us. We capped the evening by hooking this wooden box to my hifi. Our jaws dropped each time we played an LP!
In the ensuing days, I did further evaluation and indeed, these Finemet MC transformers are doing something extra special. My only reservation was, in spite of the potted construction, the FM-MCT1s are more susceptible to hum induction compared to the Altecs and Tamuras. Even if John lined the wooden box heavily with copper shielding, I still had to keep them away from power transformers, AC motors, etc.
Kimura-san specified a 3-4 week window for delivery. So I downloaded the spec sheet, studied the schematic and ordered a cast aluminum project box from Amazon.
Within 18 days, the transformers were at my doorstep.👏
These are very well made and quite hefty! They're heavier than the TKS83s which, if memory serves me right, are about the same weight as the HM7s.
I chose a different layout for the 145mm x 121mm x 40 mm MC step up transformer chassis for neater routing of RCA cables.
Under the hood
The input and output RCA jacks are on the backside mounted on top of the chassis. Only the ground lug was mounted on the side.
I installed the 3-position gain/impedance load selector in front of the chassis.
No matter which cartridge I used - Denon DL103, -R, -C1, Fidelity Research FR1 MkII, Ortofon SPU #1s, -G, -GM, Supex SD900, etc. - male and female vocals + instruments are portrayed with 3-D presence and realism in a deep and wide sound space. The musicians are in my man cave!
Boosted by the Finemets, even the most analytical and dry-sounding MC cartridges in my stash, like the Goldbug Clement II and Sony XL44 came to life with more warmth. If that's a coloration, it's certainly most welcome!
These Finemet MC transformers seem like they were configured to resolve every note in the complex musical score and massive instrumentation of late romantic symphonies along with the wide range dynamics from pianississimo to quadruple fortes inscribed therein by the composer. They also excel in reproducing the ambience, airiness and spaciousness of the concert hall's acoustics embedded in well recorded LPs.
I finally found a pair of MC transformers which combine the organic midrange and harmonious richness of classic vintage iron + the wide bandwidth, detail retrieval, and dynamic range of modern magnetics!
Ever since I became an audio DIYer, I pride myself in not being impulsive about upgrading components in my hifi. This is a rare exception!😉
CODA
As luck would have it, last week we had a family get together because a cousin based in Tokyo was visiting and brought some goodies!
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.🤔
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.
The above idler wheel was resurfaced by Gary of VoM. 👍
Even if the rubber motor mounts were still supple, I replaced them with springs. A nice lesson I learned from servicing my NEAT P58H.
To my ears, the spring mounted motor + 8 mm ball bearing/nylon countersunk washer thrust pad help lower the noise floor.
Realistic Mark 7 stepped pulley specs
Dynax P-9
These pics were sent by a blog reader.
It is essentially the Realistic Mark 7 above with a different inscription on the badge.
