Motorola SK-29M Restoration

[stbasil]

Finally have the changer sorted:

1. After cleaning and lubing, it seemed to track OK at about 3.8 grams, except when it got near the end of the record, it would start skipping back one groove. Finally figured out that the skipping started when the trip finger travelled far enough to contact the trip link. So, I took the the trip link out (again), straightened it so that it was flat and had an true 90 degree bend, cleaned off all the lube that I had put on it , used a nail file to smooth off the edges, inside of the openings, and the surface of its tab where the trip finger makes contact. Thoroughly cleaned the surfaces where the trip link slides and made sure they were smooth. Left it naked, no lube. I think I remember seeing/reading somewhere that the aluminum-to-steel interface is lubricated by the aluminum itself, assuming everything is very clean. After that work, no problem with tracking towards the end of the record!

2. The Stereo Review test record showed some low frequency mistracking, so I ended up setting the tracking force at about 4.5 grams. The crude tracking spring adjustment really does not allow for much precision, lucky to get within .5 grams of what you are shooting for!

3. Now, the rumble: It was pretty bad, and also one of my ABBA records sounded pretty strange, too--weak bass, shrill midrange. But, another record with big band music did not sound bad! One thing I noticed was that if I turned the balance control all the way left or right, the bass came back, but was gone in the middle of the balance setting. Aha! Classic phasing issue, but all the speakers were in phase, and changing one of them made no difference. I figured the cartridge channels must be out of phase, so I swapped connectors on one channel on the cartridge, and Voila! everything was perfect--great sound on both records, and the rumble disappeared. I suppose the out of phase condition meant that the vertical component of the rumble was emphasized. When I first installed the cartridge, I went by Gary's diagram on the VM website (below) for wiring, assuming that this was a "Modern" Tetrad, thus it would have the "Modern" pinout. But, that clearly was not the case.

CartSubs-TetradWiringModern.jpg (50.9 KiB) Viewed 105 times

Now I need to start in earnest on the cabinet and getting that escucheon re-labeled. Unfortunately, cabinet work has to be done in the garage, and it gets pretty hot in the summer, especially when my wife returns from errands and parks her hot car (daytime highs are in the mid-to-upper 90's every day, now)!

[electra225]

I have a VM 1257 in a Motorola portable stereo that tracks nicely at 3 grams. None of the rest of my VM's will track very well under about 4 grams, and they like 5 grams better. You are right, the springs on the tone arm don't allow for fine tuning the weight. You get what you get. GE C-100 ceramics track strictly at 5 grams. Great ceramic cartridges of which I own three. The Tetrad in the Motorola will track really light. I forget the model number. Most of the EV cartridges in Magnavox stereos track at 4.5 to 5 grams and sound really nice. Nice job on your project. I can't wait to see the cabinet when you get it done. You do nice work.....

[TC Chris]

For a dry lube, I'm fond of paraffin wax. You can wipe it down to a fine film after application. I use it for sail tracks (waterproof, clean) door latch strikes, all sorts of things.

Chris Campbell