Author Topic: Motorola Stereophonic SK107 - Phono with Vibrasonic  (Read 1486 times)

Motorola Minion

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Motorola Stereophonic SK107 - Phono with Vibrasonic
« on: April 20, 2018, 02:32:41 PM »
I picked up another Motorola on a trip upstate after seeing on CL and being the only one willing to pony up $25. Its the SK107 ($300 new), which has no radio but does have the "Hammond-licensed" vibrasonic unit built by Gibbs Manufacturing of Janesville Wisc. It is one of the more economical three-channel models having a 10" woofer, two 6" mids and two 3" cone tweeters. I am expecting to sell this one, as my other two are more expensive models, not to mention a tad LOUDER :P

I opened it up to see a the same pre-amp used in more expensive models, but an interesting amplifier that uses two SE 6BQ5 (Mullard OEMS) and the usual pair of 6V6GTA for the push-pull bass channel.

It looks similar to my SK112 ($605 new) but the amp is 20 watts versus the usual 51 watts. Both have the same early-American cherry veneer, not the sought-after Drexel cabinet models that many seem to have and are usually priced accordingly.
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Dave

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Re: Motorola Stereophonic SK107 - Phono with Vibrasonic
« Reply #1 on: April 20, 2018, 02:34:13 PM »
More pictures - the labels in these chassis are awesome. Only one electrolytic in the preamp and four dipped-paper caps that tested good that I replaced anyway. The resistors all were within tolerance, controls cleaned with Deoxit D5 and tube pins and sockets cleaned with standard contact cleaner ECG-branded.

For the amplifier, only (3) 47mf @450 volt and (1) 220 mf@50v are needed. I will test resistors of course. The real work is in the record changer, where I expect the most money to be invested, likely a idler pulley and a replacement cartridge for the Astatic 133D.

Only the two 6V6GTA made by Tung-Sol are weak. Fortunately, I have two Sylvania GTAs that test much stronger.


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Bill

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Re: Motorola Stereophonic SK107 - Phono with Vibrasonic
« Reply #2 on: April 20, 2018, 08:17:35 PM »
That really looks nice and should sound great when you are done.  Since you will have had lots of practice....want to do mine?  ::)

So with that picture comes questions: What's the unit with its back open?  I guess the other is not a question.....I love the Grand Prix.  :)

Bill

Bill

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Re: Motorola Stereophonic SK107 - Phono with Vibrasonic
« Reply #3 on: April 20, 2018, 08:21:15 PM »
Sorry for my previous question...I just noticed the caption under the picture with the two stereos.  I still love the Grand Prix.

Bill

Motorola Minion

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Re: Motorola Stereophonic SK107 - Phono with Vibrasonic
« Reply #4 on: April 23, 2018, 12:12:46 PM »
Thanks for the notice, Bill,  The Pontiac is my only link to a simpler time. And after 30 years of owning, partially restoring and barely driving it, I have been priced out of the market again. Cars have become an expensive hobby. the 1969 GP is probably my last one of this era, I have taken to collecting older records and more abundantly, the equipment they were played on. Nothing is as close to working on an old car of those days than working on a Motorola, or Fisher, or RCA Victor.....that was never serviced!

Your Motorola would be welcome in my shop, but only if you had time to wait. I do only a few jobs per year - I have to take burn-in seriously. My last customer's console was a Packard Bell with a V-M changer, and it took 6 months overall to work out the quirks before it went back. The 3-month random testing as shop musical accompaniment while working on three of my own, ones I should sell of course. There is nothing a former TV-repairman hates more than a call-back! >:(

Most guys my age were late to the party in the early 80s' and too young to afford the "real" desirable muscle cars (todays Barrett Jackson prices notwithstanding) so we settled for sleepers being neglected at the time. Nobody wanted the gas-hog big-boned GM and MoPars when the market was flush with GTO's, 442's, GS-Skylarks, Cuda's, Chargers and 340 Duster/Darts then selling for less than $10K usually. But as we saw the compromises Detroit was making in the late 1970's we went all-in in for the cars made before the ham-fisted pollution controls and unleaded gas.

But once you settled for next best, generally an example of "all-the-toys" big-block beasts, that were loaded and lower mileage, you cant resist them. The 1960's Buicks and larger Chrysler Products discussed on this forum are enough to make me want one.
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Dave

Bill

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Re: Motorola Stereophonic SK107 - Phono with Vibrasonic
« Reply #5 on: April 23, 2018, 07:14:06 PM »
Dave,

Yes that was a simpler time, and I remember it all too well!  In 1963 my parents purchased a brand new Pontiac Grand Prix.  What a car!  It was beautiful and to this day I have never seen another 1963.  I have seen 1962's and 1964's at car shows but never a 1963.  I so wish I had that car today. Hang on too yours and enjoy it in between working on all those stereo's.   :)

Bill

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Re: Motorola Stereophonic SK107 - Phono with Vibrasonic
« Reply #6 on: April 24, 2018, 02:33:09 PM »
My late uncle bought a 1963 GP when he was 18, after my grandfather passed away. It was quite a car for a young-un to have and he once recalled it had the 318-bhp tri-power 389. He married two years later yet it was a daily-driver, then he started racing a big-block 68 Chevy II and switched to trucks as daily-drivers - Chevrolets C10, ElCamino and a K5 Blazer, only getting a 71 Grand Prix and later 77 TA for my Aunt.

I never did ask him why he couldn't have waited a year and got a GTO - LOL.
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Dave

TC Chris

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Re: Motorola Stereophonic SK107 - Phono with Vibrasonic
« Reply #7 on: April 24, 2018, 09:08:53 PM »
The mother of one of my high school buddies was a teacher, a bright and devoted lady like a lot of teachers.  She had a 1963 GP with the Tri-Power option.  I could never quite figure that one out.  She wasn't a lead-footed driver.  But oh, did that car make my heart go pitty-pat, with that classic 1963 design, the GP's special concave rear window (shared with the Olds Starfire), and the big 389. 

Bill

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Re: Motorola Stereophonic SK107 - Phono with Vibrasonic
« Reply #8 on: April 25, 2018, 06:14:59 AM »
Amen!

Bill

electra225

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Re: Motorola Stereophonic SK107 - Phono with Vibrasonic
« Reply #9 on: April 25, 2018, 08:15:46 AM »
Pontiac and Oldsmobile had the nicest interiors in 1963.  Made a Buick look like a school bus interior.  My grandpas' brother bought a new '63 Olds Starfire and bought his wife a '63 98 Holiday hardtop.  They both had bucket seats and floor shift console.  The 98 was all white and the Starfire was burgundy with three-tone interior.  My issue with Pontiac and Olds was that they were burdened with that old clunky Hydra-Matic transmission.  Dynaflow was much smoother.

Did you know that Cadillac had the smallest engine of all the GM divisions in 1963?  Pontiac had a 421.  Chevrolet had the 409.  Buick had a 401.  Olds had the 394, while Cadillac soldiered on with its dinky 390.  They cured that in 1964 with the magnificent 429.
I don't need Google.  My wife says she knows everything.

TC Chris

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Re: Motorola Stereophonic SK107 - Phono with Vibrasonic
« Reply #10 on: April 25, 2018, 09:44:44 PM »
My '65 Starfire coupe has the then-new Turbo-Hydramatic, but for some reason I always like the sound of the last Hydramatic before that--Slim-Jim?  It wound out a bit in 1st and then settled into a low burble in the next gear.  The Turbo-Hydro was a superior device but didn't sound as good with a big V-8.

My buddy's grandfather had a '61 Starfire convertible, silver gray with two-tone red leather interior.  I still lust after it.  What a glorious automobile.  He traded it for a '64 Starfire coupe and handed the '61 to my buddy's mom.  Later she got the '64, nice but not the smashingly elegant thing that the '61 was.

Chris Campbell

Alfista

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Re: Motorola Stereophonic SK107 - Phono with Vibrasonic
« Reply #11 on: April 25, 2018, 11:31:12 PM »
My mother (5'2 and about 90 lbs) seemed to have a thing for big cars.

 My favorite was a 1970 Lincoln Mark III. 2 door with a looong nose and (relatively) short deck, 460cid with 365HP. I ran a 15 sec quarter at 90+mph on our dirt road with that thing, starting on a curve and ending uphill - only about half of it was straight and flat.
 
 A bit later, when I was just old enough to drive legally, I found that it would go at least 129 mph and that it had more kahunas than I did. A bit of floating convinced me that I was not a good enough driver to take it farther, and we should slow down before we become part of the landscape.

 At my age now, I'd trade a kahuna for a good Mk III.

-Tim

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Re: Motorola Stereophonic SK107 - Phono with Vibrasonic
« Reply #12 on: July 03, 2018, 03:36:15 PM »
My mother (5'2 and about 90 lbs) seemed to have a thing for big cars.

 My favorite was a 1970 Lincoln Mark III. 2 door with a looong nose and (relatively) short deck, 460cid with 365HP. I ran a 15 sec quarter at 90+mph on our dirt road with that thing, starting on a curve and ending uphill - only about half of it was straight and flat.
 
 A bit later, when I was just old enough to drive legally, I found that it would go at least 129 mph and that it had more kahunas than I did. A bit of floating convinced me that I was not a good enough driver to take it farther, and we should slow down before we become part of the landscape.

 At my age now, I'd trade a kahuna for a good Mk III.

-Tim

Funny thing, the 455 in this GP ran a 15 sec quarter at 93 mph at a drag strip in its previous body. Nothing like a large mass in motion-lol.
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Dave

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Re: Motorola Stereophonic SK107 - Phono with Vibrasonic
« Reply #13 on: August 16, 2018, 12:35:17 PM »
It is just too hot, muggy and awful to enjoy my old car sitting next to it, I manage to make progress on this junior Motorola Stereophonic. All I need is a good fan and some fantastic sounds to be happy in the garage these days.

It's been belting out Henry Mancini's greatest hits LP and Three Dog Night CD. It sounds with these extreme music genres like it should too ;) The chassis, Both preamp and amp have been recapped, cleaned and tested. Its nice to NOT have a tuner in this compact model but it was an option suffix-FM.

After plugging in the tubes and powering up, I measured power supply and tube voltages to find all within a small range of spot-on with the Sams schematic. I installed a terminal strip between the 6BQ5's and 6V6's which allows easy measurement of output tube cathode voltages and confirming resistor values without removing the chassis, held down with 10 bolts. The 6V6 pair for the bass/vibrasonic channel is about 20 volts and each of the single-ended Mullard-sourced 6BQ5/EL84 were a bit higher than listed at 8.25 and 8.5 volts. Mullard and Amperex tubes are considered valuable mainly due to longevity. Many of the original 6BQ5 used in Zenith and Motorola plus a few Maggies were either "made in great Britain (or Holland)". USA mfrs made great 6V6 and 6L6 but a difference with a 6BQ5 is noticeable with the ear and confirmed with a meter: European-made EL84's have higher quiescent cathode current set-points. I can expound further once I restore my 3 RCA's that all use 6BQ5, bothe single-ended like this and push pull, in a Fisher Electra 7 using a 481A amp and a Magnavox Symphony with the 9300 amp. .

After playing some demanding orchestral tracks on the record changer (borrowed from my restored Motorola using a Sonotone 9t cart) and through the radio (using the stereo input option), using a classic Rock CD - The cone tweets sound great, but I wonder what subbing in some Mag Kilocycle horns would sound like. 8)

This console is the entry-level stereophonic yet almost as rowdy as my two bigger Stereophonics both using 6 x 6V6 and a 12" or 15" woofer. Specs say EIA 20 watts for the little guy and 51 watts for the bigger ones. 

The loudness is great at 3-4, staging with wide open sound - but as you pass 7, the Bass needs to be dialed back from 8 to 6, or else the 10" woof gets saturated. The vibrasonic effect barely worked until I saw a shipping pin still in place to keep the reverb tank springs from moving. I was wondering what that long string from the reverb was. A tage was at the other end. It was gone but I bet it stuck out of a back cover hole and instructed you to "pull out the string" after the console was delivered.

This console was never serviced, yet working as most are found. This will be confirmed when I start working on the 1200 series V-M changer. For now, im using my other changer while I work on it. Im waiting a week to do that for more Zoom-spot turbine oil to come in the mail.

For now, the cabinet is really dirty so I have to do that in the meantime - Ill post that easy clean-restore-a-finish and wax next.
« Last Edit: August 16, 2018, 01:05:19 PM by Motorola Minion »
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Dave

Bill

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Re: Motorola Stereophonic SK107 - Phono with Vibrasonic
« Reply #14 on: August 16, 2018, 08:36:41 PM »
Nice work Dave!  One of these days I'll start on my Motorola.   ;)

Bill