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Consoles => Motorola => : TJ January 10, 2021, 08:02:57 PM

: Motorola SK52W
: TJ January 10, 2021, 08:02:57 PM
I am soooo glad to see the forum back up and running again!

Just today, I picked up a beautiful SK52, which is the Drexel Declaration cabinet. Had I not Frankensteined my '58 Magnavox Continental into a '58 Concert Grand, this would have replaced it.  This is another console that I am restoring the electronics and flipping, and may already have it sold to a close friend. 

I have worked on a few Motorolas, and this, by far, is the most complex unit that I have seen from Motorola.  Being a Motorola, it has one of their awesome three channel amps, but they used ECL82/6BM8 tubes in PP to power the left and right channels and a pair of EL84/6BQ5 in PP for the center channel. Those 6BM8 tubes are not cheap to replace if they are bad, fortunately, all of them in this amp test nice and strong.  The other Motorolas I have worked on were all PP 6V6 for Left, right, and center channels.

Where it gets weird is the vibrasonic unit has its own amp and pair of speakers.  The vibrasonic amp has a 12AX7 feeding two more 6BM8 tubes that are in PP.  All of the other Motorolas that I worked on had the Vibrasonic as well, but, it just fed back into the preamp and fed the main amp speaker system. 

The system is fully functional and I ran it for about 15 minutes to see what was and wasn't working. It needs capacitors done, the Main filter can on the amp was starting to get warm while I was using it, it was probably reforming, but I don't trust it. It also needs a new cartridge on the record changer, the left channel is a little weak compared to the right.  Everything else works perfectly.  The drive wheel on the changer is, surprisingly, in excellent shape, the changer functions perfectly, all of the tubes test very strong, most in the amp have been replaced at some point in the '70s or '80s. The radio works great in AM and FM and the AFC works great on FM.  The gimickey speaker isolator switches work, which is cool, not sure how often they were ever used LOL.

The one thing I wish it has was the MPX adapter for Stereo FM.  I have a little standalone HeathKit mpx unit, that I would se if I were keeping it, but It would be best to find an actual Motorola MPX unit.  Time to scour eBay and pay too much...

Hopefully the pictures start working soon and I can post some pictures of this beauty!

: Motorola SK52W
: TJ January 11, 2021, 06:23:44 AM
Here is what the amp for the Vibrasonic system looks like: https://www.ebay.com/itm/Mullard-Blackburn-ECL82-6BM8-PP-Mono-Tube-Amplifier-Motorola-HS-862A-Amp/143208409661?hash=item2157e2ea3d:g:eaMAAOSwNcZcrLxz 

: Motorola SK52W
: Motorola Minion January 11, 2021, 11:55:27 AM
Hi TJ, For a customer who bought my SK107 as his first working 3-channel, I am working on his SK28 and an SK-55, which is like yours.

I honestly did not believe what I was seeing for the vibrasonic stage when I finally got the schematic for the SK-55 ( I had to order the Sams from Moyers Electronics).

Two of my Motorolas (SK112 and SKR151) both have all 6V6, and the older 2-ch stereo models use 6BQ5 (SK-32, SK13 and SK17) so the 6BM8 circuit is already unfamiliar. I will be working on this one soon but I do not see an FM adapter in any of them.

: Motorola SK52W
: TJ January 11, 2021, 12:20:32 PM
From what little time I have been able to listen to the SK52, I do like the this vibrasonic system over that in my SK112.  With the SK52 having it's own amp and speakers, the reverb effect is as obnoxious as on my Sk112 which is pushing the effect through all of the speakers and over-coloring the sound even at low levels of reverb added. 

I am really looking forward to seeing how this restore goes.
: Motorola SK52W
: Bill January 11, 2021, 07:50:21 PM
Hey Trevor!  We have something almost in common.  You just got a Motorola SK52 in Drexel with reverb.   I have a Motorola SK76 in Drexel with reverb.  Same amp as yours and same little amp and separate speakers for the reverb.  The difference between yours and mind is the cabinet.  We both have the same basic cabinet except mine has short legs and two lids.  Changer on the left, controls on the right.  Does yours have a 12" or 15" woofer?  Mine has the 15".  The other big difference is yours is pristine, and mine looks like I pulled it out of the dump.  I have not resorted mine yet, it's just had a complete scrubbing before I brought it into the house.

Bill
: Motorola SK52W
: TJ January 11, 2021, 09:31:08 PM
Hey Trevor!  We have something almost in common.  You just got a Motorola SK52 in Drexel with reverb.   I have a Motorola SK76 in Drexel with reverb.  Same amp as yours and same little amp and separate speakers for the reverb.  The difference between yours and mind is the cabinet.  We both have the same basic cabinet except mine has short legs and two lids.  Changer on the left, controls on the right.  Does yours have a 12" or 15" woofer?  Mine has the 15".  The other big difference is yours is pristine, and mine looks like I pulled it out of the dump.  I have not resorted mine yet, it's just had a complete scrubbing before I brought it into the house.

Bill

The Motorola in my picture is my SK112, which was my first console, and the one I use to listen to the radio in the morning while I get ready to work, it has an excellent FM tuner.   

Here is the SK52 that I picked up on Sunday: https://www.facebook.com/marketplace/item/392459048494721 (https://www.facebook.com/marketplace/item/392459048494721) It has the dual lids, 15" woofer, and yes, this one is pristine as well. 
: Motorola SK52W
: Bill January 12, 2021, 07:54:15 AM
Well, another senior moment for me!  :-[   I actually have a SK52W as well, I do not know where I got the SK76 I thought I had.  Except mine still has short legs and does not look anything like yours as far as the cabinet goes.  Some where back in the forum I wrote about the SK52 when I got it.  I can't remember if I included photos or not, but they would not show up right now anyway.  I'm looking forward to more about your SK52 Trevor.  Please keep us updated, especially with the way it sounds that way I have something to look forward to if I ever get to mine. Sorry for the senior moment.

Bill
: Motorola SK52W
: TJ January 12, 2021, 08:17:22 AM
Well, another senior moment for me!  :-[   I actually have a SK52W as well, I do not know where I got the SK76 I thought I had.  Except mine still has short legs and does not look anything like yours as far as the cabinet goes.  Some where back in the forum I wrote about the SK52 when I got it.  I can't remember if I included photos or not, but they would not show up right now anyway.  I'm looking forward to more about your SK52 Trevor.  Please keep us updated, especially with the way it sounds that way I have something to look forward to if I ever get to mine. Sorry for the senior moment.

Bill

It would be interesting to see what your 52 looks like as it sounds like it may have been mislabeled from the factory. 
: Motorola SK52W
: TJ January 13, 2021, 09:27:01 AM
Last night I went through and recapped the main amp and the Vibrasonic amp. On both amps there was a 10uF cathode bypass capacitor for the 6BM8 tubes that was completely dead (showed no capacitance and tested as a resistor), there was a 100uF cathode bypass capacitor (which is the 4th section of the main electrolytic capacitor can) for the 6BQ5 tubes in the bass channel that was testing at 150uF and was showing high ESR on the capacitor tester and it was replaced as well as the other three sections of the main filter can.

On the main amp, I replaced all of the ceramic capacitors with poly caps, except for the two that were bypass caps, and the two 35pF NP0 caps.  One thing I have noticed working on the old tube equipment is the ceramic disc caps always seem to test below their rated capacitance, usually at the rated tolerance level, 10% caps test 10% under, and 20% caps test 20% under. The new Panasonic poly caps test spot on; I doubt that it will make much of a difference, but it makes me feel better LOL!

I left the ceramic caps in the vibrasonic amp, as mentioned earlier the Cathode bypass cap was replaced, and the 10uF filter cap was also replaced.  It's a cute little mono PP amp, I kinda wish Motorola would have continued this design for their vibrasonic units after 1960/61.

The amps will get reinstalled tonight and get tested.  Then it will be time to tackle the tuner and the two electrolytic caps that are in the tuner/preamp and replace any of the ceramic disc caps that are in the audio path.
: Motorola SK52W
: firedome January 13, 2021, 10:42:08 AM
We had a Motorola 3 ch console, 1962 or 63, modern style walnut, had the legs with the "bridge" between them and the big round dial control panel. 6V6s in the amp w/ the original Motorola tubes, and a 15" center woofer w/ 2 way mid + tweeter for the side speakers. Had an awesome sound, can't share my pic yet. Motorola made some excellent consoles.
: Motorola SK52W
: TJ January 13, 2021, 11:15:30 AM
We had a Motorola 3 ch console, 1962 or 63, modern style walnut, had the legs with the "bridge" between them and the big round dial control panel. 6V6s in the amp w/ the original Motorola tubes, and a 15" center woofer w/ 2 way mid + tweeter for the side speakers. Had an awesome sound, can't share my pic yet. Motorola made some excellent consoles.

The Motorola you are describing sounds like it is the SK77, which is the next version of the SK52.

This is the 4th Motorola that I have restored. All were still working, except for the SK75 that had bad tubes.  Motorola like using disc capacitors, so the only thing to fail on them were the Tubes and Electrolytic caps, and this is the first Motorola that I have done that had bad electrolytic caps. 

Motorola had excellent components, and they have always sounded really, really good.  Judging from the 1962/63 sales brochure that is in the Downloads section, they were not cheap either.  The SK77 in 1962/63 was $650.  That was in the same range as Magnavox Imperials of the same time.  (The imperial amp was rated at 30 Watts output, the Motorola amp was rated at 51 watts output)  I kind of wish Motorola would have made a competitor to the Concert Grand, it would have been spectacular!
: Motorola SK52W
: Bill January 13, 2021, 06:28:47 PM
It sounds like you are really making progress.  Once done, and I know you said you were going to flip this, do you think you will change your mind?   Keep this, and sell your other Motorola?  This one was a top of the line!  Check your email, I'm sending you a photo. 

You mentioned the Downloads section in your post, is it up and running and I just have not figured out where it is? 

I'm looking forward to the finished Motorola and a report on how it sounds.  :)

Thanks Trevor,
Bill
: Re: Motorola SK52W
: TJ January 13, 2021, 09:00:37 PM
It sounds like you are really making progress.  Once done, and I know you said you were going to flip this, do you think you will change your mind?   Keep this, and sell your other Motorola?  This one was a top of the line!  Check your email, I'm sending you a photo. 

You mentioned the Downloads section in your post, is it up and running and I just have not figured out where it is? 

I'm looking forward to the finished Motorola and a report on how it sounds.  :)

Thanks Trevor,
Bill

The downloads section is still there, a "hidden" button to the right of the photo gallery link on the homepage. 

: Motorola SK52W
: TJ January 13, 2021, 09:15:54 PM
This evening has been productive on the 52.  I pulled the tuner out to replace caps, and I only had to do two!  A 10uF filter, and an 8uF on the FM detector circuit.  Every other cap was a ceramic or poly cap.

I find it pretty awesome that in 1960, when this SK52 was built, that Motorola had stopped using paper caps.  The tuner section was full of the early red poly caps and ceramic disc caps.  All of those old poly caps still test spot on for what they are rated so I just left them.

I wish I could say the same for the Philco that I worked on for a friend this summer.  It was a solid state unit from 1966 or 1967, and it was FULL of original paper caps, they look just like the ones I pulled out of my 1938 Philco radio. Needless to say, I was shocked to see those in there when I went to service the stereo for him.

I have put everything back in the cabinet, hooked up all the wiring, and have been listening to run for the last hour.  I have a little bluetooth receiver plugged into the tape jacks, and it sounds great, like a Motorola.  I want to use this for a few hours over the next week to make sure everything stays working on it.

I have ordered a replacement cartridge for the changer, once that's in and thoroughly tested, it should be good to go!
: Motorola SK52W
: Bill January 14, 2021, 07:48:49 AM
Congrats on a successful, almost done, rebuild.  I wish I was there to hear it, like I said before maybe that would give me the ambition to do my Motorola SK52 next.  I hate to do it and put the all the components back into a cabinet that needs totally refinished.  Maybe next spring I will start on mine.  I sure wish all of the little boxes were marked and easier to see, that sure would help.  Have you found a way to make the photo gallery work?   Have you decided to keep this one, or flip it?                                                                                                                                                                     

Bill
: Motorola SK52W
: firedome January 14, 2021, 10:54:54 AM
Nice work Trevor, well worth the effort. Every Moto I've ever heard sounded excellent. I also way prefer their lift-up lid to the sliding type, which look cheapo to me, one feature of Maggies that I never cared for. Even my semi-BOL Dumonth has a very nice cabinet and liftup lid. it's frustrating not to be able to post any pics!

: Motorola SK52W
: firedome January 14, 2021, 10:56:12 AM
Nice work Trevor, well worth the effort. Every Moto I've ever heard sounded excellent. I also way prefer their lift-up lid to the sliding type, which look cheapo to me, one feature of Maggies that I never cared for. Even my semi-BOL Dumont has a very nice cabinet and liftup lid. it's frustrating not to be able to post any pics!
: Motorola SK52W
: TJ January 14, 2021, 07:03:43 PM
Nice work Trevor, well worth the effort. Every Moto I've ever heard sounded excellent. I also way prefer their lift-up lid to the sliding type, which look cheapo to me, one feature of Maggies that I never cared for. Even my semi-BOL Dumonth has a very nice cabinet and liftup lid. it's frustrating not to be able to post any pics!

Thanks!


I agree, I've never cared for consoles that had sliding lids, except for the Maggies that have the sliding glass lids like my Continental, the glass lids give it a more high end feel.

Right now I have the 52 playing the Piano Bar playlist from Apple Music: https://music.apple.com/us/playlist/piano-bar/pl.fc0d9d21c13c46149110dfd8dd844896 (https://music.apple.com/us/playlist/piano-bar/pl.fc0d9d21c13c46149110dfd8dd844896) I like this play list as is has a lot up upright bass, piano, and high hat, so you get to listen to the entire spectrum that the console can play.  The 52 is really nailing the high hat hits, they are crisp and clear, the piano rings through, and the woofer handle the upright bass like a champ!  On instrumentals like this, I like to set the vibrasonic to 2 to 3, that little bit of reverb gives instrumental music a nice touch.

This will be a hard one to sell, but, if it is the close friend that buys it, I will still get to see it and enjoy it.
: Re: Motorola SK52W
: Bill January 15, 2021, 07:59:52 AM
I too agree with the sliding top thing.  The glass tops, like my Berkshire, make it more high-end but leave you no place to put things.

I just checked out the Apple Music.  The piano bar has some really good music, and artist that I really like.  Errol Garner's "Misty" is one of my favorite arrangements of all times.  And one of my favorite songs of all times is "A Nightingale Sang in Berkeley Square."  Marion McPartland did her arrangement on Piano Bar.  That song played by the right organist on a Theater Pipe Organ is one of the most lush pieces of music every written.  Here's the song played on a Digital Theater Pipe Organ by an artist that knows what he is doing.

https://www.youtube.com/watch?v=PXEkQdcuncI&feature=share

Bill