[Boatanchors] National HFS Coils

[Cal Cotner]

      I took a look at the A,B and C coils in my HFS, and they vary a  
bit.  It looks as if the turns are spread and compressed on a couple  
of them.  I didn't look at the schematic, but I assume one is the  
mixer input coil and the other is the local oscillator coil.  I would  
think that some compression or spreading of the coils might have been  
done at the factory in order to accomplish two things.  One would be  
to ensure that the tracking of the dial calibration is reasonably  
close to the calibration plate on the front of the receiver, and the  
second is to have the mixer input coil track the local oscillator  
tuning across the band.  However, there is an antenna trimmer  
capacitor which might compensate somewhat for imperfect tracking  
between the mixer input tuning and the local oscillator frequency.   
So I wouldn't be surprised to see some deformation of the coils in  
their plug-in forms.
      One way to check the tuning and tracking might be to first  
check the local oscillator tracking with the frequency to which the  
receiver is tuned.  Then one might insert either an iron or brass  
loaded tuning wand into the coil form and see if the tracking gets  
worse.  The same thing could be done with a signal generator feeding  
the receiver to see if the mixer input tuning improves with insertion  
of the wand.  Not sure wherre one would want to set the trimmer  
capacitor when doing the latter.
      Anyway, I hope this is of some help to W0QFC who posed the  
question.  I'm not sure I could take a deecent picture of what the  
coils in my HFS look like.
73,
Cal K4JSI