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Author Topic: Collins 51J4  (Read 2785 times)
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k5ygc
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« on: November 16, 2011, 08:32:39 AM »
Is there a way to change the 6 kc filter to 8 kc. Maybe even connect the 6&3 kc filters together?
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Steve - K4HX
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« Reply #1 on: November 16, 2011, 08:54:59 AM »
That won't work. Look for a 9.4 kc filter. You'll see one for sale once in a while on the web. Also, Fair Radio used to have them.
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k5ygc
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« Reply #2 on: November 16, 2011, 09:05:38 AM »
OK thanks for the reply.
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w3jn
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« Reply #3 on: November 16, 2011, 10:51:50 AM »
You can remove one of the filters and bridge the filter input and output with a small capacitor - 150 pf or so as I recall - which then broadens the selectivity to the point where only the L/C IF transformers' selectivity is in play.  As I recall it's perhaps 10 kc but the skirt slope is pretty gradual.

The hell of the 51J-4 is it's a 500 KC IF, and filters are quite a bit rarer than 455 KC units.
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