[Hallicrafters] Black Beauty capacitors Beware

[David C. Hallam]

Jim,

What is the recommend procedure to sweep the the filter?  I do not have 
a sweep generator but do have a good assortment of test equipment.

David
KW4DH

On 3/7/2015 10:20 AM, Jim Liles wrote:
> Hi Greg,
> good assoermentr
> Exactly!  They were as good as film and legions better than ceramic.  That’s why you still see paper defined on the schematics not ceramic caps.
>
> I still would replace the paper because as they dry out or begin to leak the Q goes to the devil.  Won’t effect the .5Kc position because it doesn’t use them but when you use the higher band widths, especially the 1Kc, they will widen because of the denigration of the Q.  May not be obvious but if you sweep that filter system it’s obvious.  The band center skew jumps out at you when using the ceramic caps.
>
> In any case the paper at their worst will out perform ceramic unless they are shorted or open.
>
> One measure is, you should be able to tune in an SSB signal in the 5Kc position and dial right down through 1Kc and still clearly copy that conversation without touching the BFO and tuning to peak for clarity.  The best definition that describes what you have to do when incorrect caps are installed is “You have to be a human I.F. shift mechanism”  You have to tune an SSB signal then tune slightly back and fourth for peak strength while adjusting the BFO for clarity.  You don’t want to go there, let the radio do it for you.
>
> One thing that I didn’t mention is the 390 ohm resistor will be well above 420 ohms.  Those resistors are very critical.  Get it right on or 5% below not above or the 5Kc position will droop excessively.
>
> Kindest regards Jim K9AXN
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