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Old 21st July 2014, 03:28 PM   #1
diyAudio Member
Join Date: May 2014
Default Motorola console recap question

Hi all,
First, apologies if this is the wrong place for this thread.
Now on to my question.
I recently acquired a Motorola 3 channel amp ( 1 low pp , 2 high se) that I'm thinking of restoring (as in changing parts of - mostly because of a muddy right channel).
I plan to start with replacing the resistances and capacitances of the high channels and would like some advice fromon what parts could be used from wiser people.
Specifically , what voltages do you think i should use?
The capacitances are rmc make ceramic discs with units mentioned in jF. Not sure what jF actually means... Is it microfarads?
there are also what look like metallic Motorola 8MFD caps with 25 WVDC (what's the W here? VDC I understand). I take it I need to change these? What can I replace these with?
Finally, if I were to take a phased approach what should I change first? The resistences , the Motorola's or the ceramics. Could the muddy sound be due to a bad transformer?
I will be trying to upload images.
Any help from experienced members will be appreciated.
Attached Images
File Type: jpg IMG_20140721_191341.jpg (696.8 KB, 56 views)
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File Type: jpg IMG_20140721_191133.jpg (588.2 KB, 53 views)
File Type: jpg IMG_20140721_191649.jpg (857.5 KB, 53 views)
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Old 21st July 2014, 03:49 PM   #2
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Rod Coleman's Avatar
Join Date: Jul 2004
Location: Warwickshire UK
Electrolytic caps like the 8MFD have a short rated life, and dry out and/or leak. Muddy sound is just what they are like. 10 years is enough to get them sounding bad, though they can struggle on for decades, sometimes.

Change these first.

8MFD 25WVDC - 8F 25V (WORKING V dc). Using 10F 35V should be OK in most cases.

If it crackles, the carbon anode resistors are often the cause. Also, measure them when there's zero voltage present on the supply caps. 5% and 10% tolerance on the ones in the photo, but they might get to be 50% high, with old composition types like that.

Ceramics don't necessarily degrade, though yours look like the coating seal is broken in many instances.

Try the amp, change them if you need to.
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Old Yesterday, 03:04 PM   #3
diyAudio Member
Join Date: May 2014
Thumbs up Thanks Rod

Thanks a lot Rod,
That was very helpful. I will get the electrolytic capacitors changed and let y'all know how it goes.
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