Motorola SK-29M Restoration

[stbasil]

My first random fix on this guy is the torn off speaker enclosure door, simple enough, actually, since it's due to the glue failing on the hinge side of the enclosure. While I was at it, I found that the inverted magnet oval midrange was completely white with what may be the dreaded cadmium dust. It came off easily with a wet paper towel, as did the same, very thick coating on the inside magnet cover. Both speakers ohmed good, fortunately.

The grille cloth is in decent shape except that it has shrunk upward on the bottom edge of the doors. They didn't wrap it around the speaker board on the top and bottom, so the only thing keeping it in place is glue, and there is not enough surface area below the midrange cutout to keep it secure when it started shrinking.

I can grip the cloth and with a lot of force manage pull it down, but it of course won't stay that way. I tried carefully heating with a hair dryer while pulling, but it won't keep it from shrinking back. Any suggestions on how to fix that, apart from replacing the grille cloth? I may just end up covering the exposed lower edge with some gold tape, but that doesn't fix the waviness.

[electra225]

Check AES to see what kind of grille cloth they have. I used a cloth very similar to that on that old GE stereo I redid, had a touch more red in it, but yours has shrunken and faded. Does that cabinet show signs of being wet? PB Blaster works well on the cad dust. Spritz some on a paper towel, wipe, and the cad dust seems to stay away.

That 6X9 speaker has a 232 EIA code on it. Magnavox!

[stbasil]

Uploaded Sam's SK-29M service manual, and also a single page schematic from 1960 Beitman's, to the Uploads Amps and Tuners section. Neither of those have a tuner schematic.

[electra225]

Thank you!!

[William]

It is weird not seeing the magnet in the normal spot, and this is the first time ever seeing a speaker like that, thank you for sharing that photo.

Bill

[electra225]

Antique Electronic Supply is now called Amplified Parts. They have quite the selection of grille cloth. Hopefully, you can find something close that will work.

https://www.amplifiedparts.com/products ... lex-piping

[stbasil]

I've got some ideas of how to retain the original grill cloth--it's got a more interesting weave than the guitar amp stuff, and my wife thinks the "waves" are really cool! I'll be posting about that later...

But for now, here's a problem I've encountered. The control escutcheon was dirty, of course. I began to clean it, first washing with dish detergent, not much help, theb testing a small area with isopropyl alcohol since it looked discolored from cigarette tar. Lots of brown stuff came off, and it seemed to not affect the black text. But I soon discovered that the stuff that I thought was discoloration was probably some intentional tinting to make the aluminum appear gold to match the brass knobs. And, the text also started to smear, so this is going to be a complete strip and redo for the escutcheon

But, I had an interesting experience with AI, after reading on ARF about a guy who had ChatGPT clean up an old radio label. So I uploaded this photo of the aborted result of my cleaning:

Then, I told it to clean up the text and symbols:

Then I had it remove all color except black and replace with white

I could have done all that in Photoshop, but it was interesting to see what the AI can do and it took a lot less time!

Now, I have to figure out how to transfer the text to the escutcheon. From my research, I think there are a few ways to do this:
1. Print a reverse image onto glossy paper using my laser printer, placing the printed paper onto the aluminum and ironing the toner onto the metal, then soaking in water to soften and remove the paper which will leave the toner stuck onto the metal. Have to seal it with some clear coat, of course.
2. Print the text onto some gold foil paper and stick it onto the escutcheon, add some clear coat.
3. Use some type of dry-transfer film, similar to #1 method, but it would just peel off and leave the toner without having to soak.

I've never tried any of these approaches, so I am hoping to get some advice regarding the best DIY approach to this! Any thoughts?

[TC Chris]

Looking forward to your results. I had the same chore in the pre-computer age, on a Zenith H-725 with a rusted dial ring and kitchen grease that had attacked the numbers. My solution way back then was to paint with spray metallic gold paint, apply press-in numerals, and spray over with clear enamel. Looked good enough for office use. Your method will likely produce a more authentic look.

Chris Campbell

[Brettzky99]

Congrats, nice find. I've got a 28 and a model 30

[William]

Brett, same guts in yours as stbasil's,just a different cabinet???

Bill

[stbasil]

Have set aside the escutcheon label issue for now, working on cleaning the electronics and turntable so I can move those from my downstairs garage shop to my upstairs electronics shop. Wish I had the space to have everything on ground level!

This console was probably stored in an attic for a long time; excessive heat has worsened the aging process!

The platter mat on the VM 1200 was pretty ugly, but thanks to suggestions from some folks at ARF, it's looking a lot better! Ended up soaking in Oxiclean in the sun for several hours, before and after:

I'm sure some of you are members there, too, though with different handles, so thanks if you contributed advice!

The tubes were all original, the EL84's were all marked "Made in Holland" and the,12AX7's all looked like this.

The rectifier was marked as Motorola on its base.The 12AX7's in the preamp had a yellow dot on top, I guess they had been selected for low noise, maybe? They'll go back there, of course. Unfortunately all glass markings, except the faint type etchings, came off when I wiped the grime off the tubes!

The Sonotone 8T had its stylus, but the bridge had collapsed somewhat and some jelly-like substance is all around it, I suppose it's a damping gel that the heat caused to liquefy. I'm going to attempt to disassemble and repair it, but I'm not hopeful. Would really like to save it ...

I'll start on the electronics soon. ..

[TC Chris]

Nice job on the mat. And follow up on the cartridge repair attempt. I've got an old mono Emerson portable that a prior owner had outfitted with an 8T or 9T (memory fails). The cartridges were well regarded as ceramics go. Mine may need rescue after sitting in the repair queue for 50-odd years.

I used to be really snotty about ceramic cartridges but I'll bet that they produce higher frequencies than my ears can respond to now. The "I'll bet" is because I carefully avoid hearing tests. Don't want to know. Had an MRI for the sciatic issue and it shows other alarming things. They always do. Avoid unless necessary, and if it shows something that produces no symptoms, ignore it.

Chris Campbell

[electra225]

The good thing about a ceramic cartridge as used in a console stereo is that they don't pick up noise from a two-pole phono motor. I have found some ceramic cartridges to be quite acceptable in performance. The GE C-100, EV 26 and 132, Sonotone 2T and 8T among the ones I have had experience with. I believe for "more modern" turntables, a magnetic might be preferable. I never understood why some folks stick their noses up at ceramic cartridges and console stereos. Heavier tone arm weight is one gripe, but I've found that if you keep the needle in good shape and if the tone arm pressure is appropriate for the cartridge you are using, that hasn't been an issue in my experience.....

[William]

Thank you for the tip on the platter mat, I will try that on one that if have. And, yes, please keep us informed with your cartridge. I sure would like to save a couple I have if nothing more as a comparison to what it did sound like compared to what a new cartridge can produce.

Bill

[electra225]

Learning to clean tubes without removing the markings is an acquired skill, best mastered by practice. I was fortunate to have my stepdad's junk tube bucket to practice on. He had a TV repair shop and never threw anything away, even if it was total junk. Art's "clean it without touching it" procedure works out pretty good as well, but, again, that is an acquired skill.

[stbasil]

After much disassembly, I have determined that the 8T cart is beyond repair.

In summary, the two little posts sticking out of the damping gel are where the saddle (Yoke? Thingy?) attaches through those two little holes, the stylus shaft sits inside the Y part. Apparently the stylus sat on the platter in a hot attic for decades. The posts are attached to the two ceramic elements inside the body.
One was deformed downward, as you can see in the photo, and the yoke attachment was also broken from the piece that held it onto the cartridge body. I removed the brass rivet and washer intending to glue it back together.

But then I broke off one of the pins, so I gave up on this, it was a long shot anyway. But, I learned a lot about how the cartridge was put together! I'm guessing that even if I had managed to get it all back together, the asymmetry of the two pins would have caused significant distortion. This video gave me the courage to try this fix, y'all might find it interesting, too.
https://youtu.be/eVCyjPm9hhM?si=p_nl655lFvrxmTWx
Now for a replacement cartridge...