The AM Forum

I'm working on 2 valiants for a friend and both VFOs won't spread to align right on 160 meters.  The 40 meter spread is ok.  Funny that both show the same symptoms.  Trying to align the high and low ends just won't spread right.  Both rigs were butchered by cbers.  I've tried padding in caps and can make it good on one end but not the other.  Any help appreciated.  The screen grid resistor has been replaced on both rigs.  WB4VFN Rich

Rich,

Are you sure the VFO tuning capacitor is properly indexed to the dial?  It should be full mesh with the dial pointer at the CCW horizontal position. 

I have never run into a problem with calibrating any of the Johnson VFO assemblies when the dial/capcitor is indexed properly.  Is there any indication that the former owners changed any of the caps in the VFO?  If the proper marked values are installed then one of them may have changed value.  These caps will have specific temperature coefficient values so replacement is not going to be easy unless you are willing to have an unpredictable drift in frequency-even worse than the norm for these VFO units  :)

Thank you and no I'm not sure.  Fact is I never paid any attention to that and had both units completely apart.  I will check into that and I'm sure that is the problem  Thanks again 73  Rich

You are welcome and I hope there is a simple solution to the calibration problem.  I ran into that with the external Viking VFO once.

73, Rodger

I would think adding padder caps will reduce the tuning range and shift it lower.

Rich,
I have had good luck getting those "dog bone" caps that Johnson use in their VFO's from Surplus Sales.  Bob, W2ICQ put me on to them as a source.  Price not to bad either.
Good luck with the project.
Regards,
Joe, W3GMS