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 Post subject: Knight 6B-127 Bad Coil
PostPosted: Sep Tue 28, 2021 10:21 pm 
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Joined: Jun Tue 17, 2008 4:11 pm
Posts: 245
Location: Mt. Rest, SC, USA
My Allied Knight 6B-127 has an open coil in the IF trap (#6 on the schematic). I believe the inductance is supposed to be 3.9 millihenries, based on calculation and by measuring the coil in a Sentinel 285P, which seems to use an identical chassis.

I have never dealt with replacing an inductor and am unsure what to look for in a replacement. :? Looking through Digi-Key, all of the 3.9 mH inductors I see are power inductors designed for power supplies, not RF circuits. Here are some I saw: https://www.digikey.com/en/products/detail/bourns-inc/RLB0913-392K/6677240, https://www.digikey.com/en/products/detail/bourns-inc/5800-392-RC/774848, https://www.digikey.com/en/products/detail/abracon-llc/AIAP-02-392K/3059896, https://www.digikey.com/en/products/detail/abracon-llc/AIAP-01-392K-T/3059854. Their inductance is often measured at a really low frequency, e.g. 1 kHz. They all have ferrite cores, unlike the original which was air core.

Some specify a self-resonant frequency, but most don't. Is this the highest frequency the inductor will work properly at? The highest I saw was only 1 MHz, which is below maximum of 1.7MHz it will see in the circuit.

I did see find a Meissner 15-2866 IF trap https://antiqueradiosandparts.com/index.php?route=product/product&product_id=2138&search=Coil&page=3, which has both the inductor and capacitor. Should I use this instead?


Attachments:
File comment: Schematic
Allied Knight 6B-127.png
Allied Knight 6B-127.png [ 559.66 KiB | Viewed 197 times ]
Bad Coil.JPG
Bad Coil.JPG [ 677.21 KiB | Viewed 197 times ]

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 Post subject: Re: Knight 6B-127 Bad Coil
PostPosted: Sep Tue 28, 2021 11:24 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 2479
Location: Lafayette, CO
Why exactly is that trap there? Does the radio work with the open coil? Craig


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 Post subject: Re: Knight 6B-127 Bad Coil
PostPosted: Sep Tue 28, 2021 11:40 pm 
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Joined: Nov Tue 14, 2017 5:09 am
Posts: 4096
Location: Austin, Texas
It looks like a trap at the IF. The radio should play OK without it.

Jay


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