[Collins] Two More 51J4 Questions

[Dr. Gerald N. Johnson]

Sure points at the filter, especially when moving the filter to a 
different socket gets the same result.

73, Jerry, K0CQ, Technical Adviser to the Collins Radio Association.

On 8/23/2013 1:05 PM, Grant Youngman wrote:
> Jerry ...
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>> I see the original circuit shows the IF tube plate current passes through the filters. DC can change the transducer, it would be a good idea to make the mod to isolate that DC voltage and current from the filter inputs
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> I've done that. I feed the plate through a 1.8 mH choke paralleled with a 56 pf cap. That goes to a .01 cap which feeds the 240 pf cap across the filter inputs (through the switch).
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> If that filter cooked, it did so before I made the change ...
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>> I don't think the filters should be that different.
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> A few dB difference would be normal. 17 dB sounds wildly off to me. Also, the filter passband is extremely ugly and far exceeds what I would call normal "ripple". By contrast, the 6 KHz filter has the classic shape with just a hint of ripple on an otherwise flat top. So all in all, I suspect it's just a bad filter.
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> Grant NQ5T
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