[ARC5] OT? bc-348 bfo question

[mac]

Two or three turns typical, number determined by cut-and-try..   
Recommend just adding , say, three turns and see if the performance  
improves.  In some receivers of the era the gimmick cap was put on the  
grid of the last IF stage to increase the injection level.

Dennis D.  W7QHO
Glendale, CA

******************
On Sep 13, 2013, at 5:37 PM, Fernando - LU2DFM wrote:

> On Fri, Sep 13, 2013 at 07:37:09PM -0400, Jay Coward wrote:
>> Check the feedback "gimmick" capacitor. It's a couple of twists of  
>> two wires.
>> Jay
>
> Thank you; I'm thinking alike. The gimmick looks like original to
> me, and it's pretty small: the wire from the BFO coil goes over the
> plate wire, but does not coil around it. I think this is too little
> coupling.
>
> My feel is that the output of the BFO is too small to get enough  
> carrier
> into the detector for moderately strong signals and up. The plate
> voltage of the triode section of the 6F7 varies between some 45 to 32
> volts as the RF gain is varied (MVC, no AGC position). That's pretty
> near what the manual indicates.
>
> Tomorrow I'll take some meticulous measurements and will decide if  
> more
> gimmick capacitance is needed or there's something wrong in the BFO.
>
> Does anyone has a photo of an original gimmick cap?
>
>
> -- 
> 73 de Fer, LU2DFM
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