Restoring a 1959 3-channel Motorola

Paul Samarin · by **Paul Samarin** » Tue Dec 11, 2007 2:38 am

Hello, this is my first post. I'm looking to restore an inherited Motorola. It had very full, warm sound for most of its life, but is old and tired.

I've never touched electronics before, so I'm seeking all the help I can get. Is this forum a good source for tips and for locating parts for this not-quite-antique beauty?

TIA,

Paul
In Southern California

Paul Samarin · by **Paul Samarin** » Tue Dec 11, 2007 7:10 pm

Meant to mention the model: "SK32"

Thanks,

Paul

Record-changer · by **Record-changer** » Fri Dec 14, 2007 6:16 pm

You need to learn to solder before tackling this. Nothing can make a fine system sound bad like bad solder joints can (and they are hard to find too).

The main thing you might want to do is replace all of the electrolytic capacitors. They deteriorate with age to the point where they either leak current or change value. Hum is the symptom of this.

Test the system after each change.

They will probably have to be special ordered, and the multiple-section caps are usually not available anymore. You might want to leave the multiple-section "can" in place (but disconnected) to preserve the look of the amplifier, and find other places inside the chassis to hide the new capacitors (which will be considerably smaller, due to new technology). Be sure the voltage on the new capacitor is greater than or equal to the voltage on the original. But get the closest available voltage that is greater than or equal to the original rated voltage. The capacitance should be greater than or equal to the original, but not too high.

Remember that electrolytic capacitors are polarized. They burst if connected backwards or connected to AC, spewing boiling electrolyte everywhere. Old ones have a + sign on the positive end. New ones have an arrow pointing to the negative end.

Most non-electrolytic capacitors do not gradually change value over time. They usually suddenly short or open when they fail. The values are critical only if they are in a tuned radio circuit or a tone control circuit.

Check the values of the carbon resistors. They change value if overheated.

Get some Caig CaiLube MCL or Caig DeOxIt 5 to clean the crud out of noisy controls.

Get some Caig CaiKleen RBR to clean the rubber idler wheel in the record changer.

Use sewing machine oil to lubricate the motor bearings, the idler bearing, the idler jockey arm pivots, and the turntable center bearing.

Make sure there is NO lubrication on the change cycle trip parts. They must be clean and dry to function.

Find someone with a stylus microscope to check each stylus.