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Old 01-12-2018, 10:16 PM
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SpaceAge SpaceAge is offline
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Replacing peaking coils

Hi, I need advice about replacing peaking coils. I am working on a Motorola that apparently uses two visibly different types of peaking coils. There are four in total, three are yellowish-white blobs (for lack of a technical term), and one that is smaller and looks like a resistor sans the colored stripes. I actually thought the "blobs" were spider egg nests when I first looked at the chassis underside, thankfully not the case . Anyways, the Sams lists DC resistance values so I took some measurements. The brown one and two of the blobs are ok, but the third blob tests open. If I have to replace one, I might as well purge all of them, or at least the three nasty-looking blobs. Trouble is, I don't really know what the modern equivalent would be. I was hoping someone here could point me in the right direction. Here is the parts list and schematic. L14 is the brown coil; L15, L17, and L18 are the blobs. Thanks for the help .



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Old 01-13-2018, 01:36 PM
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Electronic M Electronic M is offline
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Congratulations you have just gotten a taste of a restoration quirk of the CT-100, 21CT55, and many humble Motorolas: Those lousy wax dipped white ceramic peaking coils.
I just changed out a bunch on my 21CT55.

Something like this should work for the 203uH L17. https://www.digikey.com/product-deta...LCT-ND/3767925
If Sam's had been kind enough to have listed the inductances of the others I could look up replacements...

In most cases, you can just short out an open peaking coil and the sets will work (albiet with changes in video response). If you have any spare peaking coils form parts sets you could do trial and error substitution.

The white ones are the only ones to worry about, they were a bad design and only seen for a few years in the mid 50's.

I also had a Motorola with those white coils, I ended up grabbing parts from the same circuits in a Motorola parts chassis a few years older.
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Old 01-14-2018, 05:49 PM
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SpaceAge SpaceAge is offline
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Quote:
Originally Posted by Electronic M View Post
Something like this should work for the 203uH L17. https://www.digikey.com/product-deta...LCT-ND/3767925
If Sam's had been kind enough to have listed the inductances of the others I could look up replacements...
This is what I was scratching my head about too. Maybe a Riders or Motorola service manual would have the info? Or I could try to track down data sheets from Motorola or Merit for the original parts but I would think that would difficult. At this point I'm not going to worry, and just proceed with the recap. I will reevaluate later and see where I'm at. Thanks for chiming in.

Last edited by SpaceAge; 01-15-2018 at 02:29 PM.
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Old 01-14-2018, 06:28 PM
madRad45 madRad45 is offline
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Here's the Merit Peaking Coil info from the 1969 catalog. I also saw of couple of the ones you need listed as available at ETF.
Attached Images
File Type: jpg Merit Transformer Peaking Coils.jpg (88.3 KB, 23 views)
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Old 01-14-2018, 10:43 PM
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Thanks for posting that, looks like I have a couple of options here...
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