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Motorola sk44m amplifier

Bluesfan1956

Bluesfan1956

New Member
I recently purchased a Motorola console record player for $5 at Habitat for Humanity. Needed new needle but powers up nice sounds good. Can only get center sub and either left or right side together. But never L+R and center. Would like to find a schematic for wiring. Any help would be appreciated. New to forum, but love the vintage equipment.
 
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Thank you very much. Very helpful
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Those 3 channel Motorola's are not your typical 2 channel stereos. The amp should have 3 individual speaker connections. One for the center bass speaker and 2 more for the individual left & right speakers. The center bass speaker produces all the bass from both the left & right channels combined. The left & right mid and tweeter speakers are full stereo except they only reproduce the mids and highs, no bass. This is why you can't just take an old 3 channel Motorola system and make it 2 channel stereo unless you have an excellent grasp on electronics and knowing how to read a schematic to convert it but they are best to being left original. They are unique in and of themselves.

I own a Motorola 3 channel console I got from my Goodwill store some 20 years ago and when I brought it home and plugged it in, I had no sound. Taking the back off revealed all. The previous owner or person was probably trying to add another pair of speakers not knowing that these are not your conventional 2 channel console stereos. 4 wires were wired to the bass channel connection and the bass speaker was totally disconnected at the speaker itself.

In your first pic, that speaker wiring looks terrible and needs to be cleaned up. Also, which speaker does that connection go to? Aside from that shoddy wiring in your first pic, let's see a pic of the other speaker connections. You might want to take out the amp to inspect and clean up.

There were so many different models. Mine uses four EL84/6BQ5 output tubes in where two are used in push pull for the bass channel and the other two are used in single ended configuration for the left & right stereo channels.
 
Thanks for your input. It is just as I bought it except for new needle for player. Haven't had time yet to go thru it and clean it up. Should have time this weekend. Will post more picks when done. Thanks again.
 
Interesting. I have four different moto's and this is the first one I noticed a circuit reset button. Mine are all two-channel. Now I can go back to bed knowing that I learned something today.
 
At least one of the ECL82 tubes says Made in Great Britain which means it is a Mullard. So if you have six of those, you are set. They are great tubes.

If you tidy up the speaker connections as Century Tek said, you might well get sound from all three channels. Even if you do, the amp will be much more reliable if you were to replace the filters caps - those in the can. I think they used four 40uF at 350V caps in the can.

Not a lot of room to mount them under the chassis, but I believe AES sells a can that will fit there. https://www.tubesandmore.com/products/capacitor-ce-mfg-350v-40404040uf
 
Here are some more photos of the wiring and speakers. I appreciate all the input.
 

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Wiring to the speakers is likely good. Its the connections to the amp that need work.

Cut off those scraggly ends, and strip off 1/2” of insulation. Tin the ends with solder. Then make a bend around your needle nose and they’ll all screw right back in there.

Those orange capacitors on each speaker will want to be replaced. Get the closest value at parts express. Those are Non Polarized. The resistors on the tweeters are likely good.

Keep hitting us up with questions as you go. This is a very straightforward project to get going once you get past the 2.1 nature of the amplifier.
 
The left Channel connection its not putting out anything. I can take either the left or right side wire and put it on the right side and it plays but nothing from the left side. All the tubes are lighting up.20190711_081844.jpg
 
Measuring voltages on the missing channel will likely point to the problem. Even without a voltage chart, you can compare it to a working channel. Best way is to use an an adapter like this to measure on the top side:
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Could be dirty tube sockets too. Try gently rocking, in a circular motion, the two tubes of the Left channel. Do you get any crackling sounds?

Also try swapping the input RCA plugs, left for right, and see if that changes anything.
 
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Better have a test meter handy if you are going to do any kind of troubleshooting. These things are easily traced out. Really not much to them.

Yes, swap your inputs. This will tell you if the problem is in the preamp or the amp. In case you don't know, the preamp (volume, bass, treble controls) also has a tube or two so that needs to be checked.

What's that tube with the piece of tape on it? Maybe the previous owner put it there to mark a bad tube? :dunno:

Since this unit uses all the same tubes, you can at least swap 5 of the other tubes in its place to see if that's the problem.

EDIT: You can also turn the amp over and see if the dead channel wiring and output transformer connect to that tube with the tape.
 
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