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| 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.
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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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.
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| 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...
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.
Overall, my ears still prefer the smaller and more affordable brother, the Altec 4722!
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.
Inspired by the sonic niceties I heard, I was undeterred so I contacted Mr. Kimura of General Transformer Sales Co. Ltd. After a few emails aided by Google translate, I finalized my order.
Gtrans.co.jp is headquartered in the same location as the former Noguchi store we visited in 2015, which is in the basement of Tokyo Radio Department Store in Akihabara.
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.👏
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| Finemet FM-MCT1 |
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!
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!😉
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| Stereo Sound Tube Kingdom Volume 104 |
If I got it right, in this survey of commercially available MC step up transformers, the Finemet FM-MCT1 was the only DIY unit.
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.
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| 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.
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| 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.
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.
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.
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.
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| 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
It is essentially the Realistic Mark 7 above with a different inscription on the badge.
I have a close affinity for the Mark-7 + A3 since this was the very first Japanese idler-driven turntable I acquired.
After going home with me to Manila and back stateside, I finally found time to try the JS 4120Ns in my preamp. After adjustment of voltages and operating points, I was impressed by the increased detail and resolution brought forth by replacing the Allen-Bradley plate load resistors while retaining the sonic aura I've come to treasure from my Bruce Berman-derived 76 > 1/2 6SN7 line stage circuit from Sound Practices Issue 13.
Unfortunately the JS 4120Ns have been out of production for quite a number of years. 😞
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| NOTE: According to the 7N7 data sheet, it has a maximum cathode to heater (filament) voltage rating of 90V. To get around the 142V at the cathode, I lifted the filament potential 65V above ground via a voltage divider network in the B+ supply. Hence, 142 - 65 = 77, which brings it back to spec. |
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| 100 Hz, 1 kHz and 10 kHz square wave output from 2 x Hammond 156C plate choke loaded 1/2 7AF7 + 1/2 7N7 cathode follower |
I tried the budget-friendly Hammond 156C plate load chokes in the circuit above on my loctal preamp as well as on my main preamp with the 76 line stage below.
Detail improved but I missed the micro dynamics and organic quality in the midrange of the JS 4120Ns. That said, I'm now using this topology in the nosTDA1541tube DAC in my main hifi set up. Meanwhile the loctal preamp line stage has been reverted back to its original state with Allen-Bradleys.
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| NOTE: This choke saturates instantly past 8 mA! |
Since the Hammond 156Cs are easy on the wallet (just like the 125ESEs I wrote about decades ago😉), why not try and judge for yourself? If you hear potential, then proceed to the nickel plate choke-equipped circuit below.😊
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| Custom wound Intact Audio 250H nickel plate chokes |
I was so impressed with Dave's nickel plate chokes👏 such that I ordered a pair for myself so I could use the JS 4120Ns for other tubes and circuits. I also confirmed that in order to get the most out of the plate load choke topology, one needs a competent winder, and nickel should be part of the equation!
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| Even if I always used more rugged 6SN7 GTA and GTB types in the cathode follower section, when I built this preamp over two decades ago, the power supply was configured so that the filament potential was about 75V above ground. |
I've always admired the sound (or more appropriately, the lack thereof) of nickel permalloy, having owned the Tamura F7002 and Tango NY15S since the 90s. Even if these output transformers are hefty beasts, which helps the low frequencies, it's not their bass response that captivates the listener. Instead, they present a very natural midrange replete with rich and harmonious overtones, which are virtues I also hear with Finemet.
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| 100 Hz, 1 kHz and 10 kHz square wave output from an Intact Audio nickel plate choke loaded 76 + 1/2 6SN7 cathode follower |
After praising the merits of exotic core material, I wouldn’t want readers to get the impression that nickel or Finemet are the quintessential elements to great sound. Tube choice, circuit topology and operating points, parts selection, etc. not to mention the synergy of components in the hifi chain, all contribute to the sonic stew. That's why I encourage audio hobbyists to listen and experiment so that they can carve their path towards their own musical satisfaction.
Although this video is merely a proof of concept, I got inspired and used my Sony A7II + Voigtlander Ultron 28mm f1.9 LTM lens mounted on a tripod rather than my usual iPhone. So plug in your Koss Porta-Pros or Sennheiser HD6XXs and (hopefully) enjoy!🎶🎹🎻
Maybe 🤔 I'll talk about my plate choke adventures with SE amps next time!😉
