[Collins] Two More 51J4 Questions

[Grant Youngman]

Jerry ...



> 
> 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

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). 

If that filter cooked, it did so before I made the change ...

> I don't think the filters should be that different.

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. 

Grant NQ5T