[frsimen]

I measured the inductance of L3 using my Wayne Kerr meter which only tests at 1kHz. It's possible that the value of L3, with its ferrite core, read lower than its true value.

If you factor in the grid circuit capacitance of the output valve and the output capacitance of V2, they appear in parallel with the L3/22pF series combination. Add in a little self capacitance for L3 and you end up with a notch response due to the L3/22pF and a higher frequency resonance due to L3 and the various strays in series with the 22pF.

I've not noticed any problems with the AT5 that would need taming. As it is a simple VFO/multiplier design, there isn't much opportunity for non harmonically related issues. The multiplier stage is stable when used on 160m, and it doesn't seem to misbehave when used on 80m.

I hope your AT5 clones don't drift as much as my real one does!

Paula