f=1/[2*pi*sqrt(L*C)]
where L is in H, C is in F, and f is in Hz.
of course actual capacitance is a little bit higher due other components in circuit.
so your circuit should be at 3.7MHz (when trimmer is on max capacitance) or some 10..11MHz when trimmer is on minimum.
personally i don't like certain things about this article:
- this is titled audio section which is hardly true, this is RF circuit (oscillator / mixer for audio / video)
- there is no real schematic, only layout diagram
- layout is without any dimensional reference (size, orientation etc do matter in RF)
- there is no indication how this stage is to be powered, positive should be at pos. end of 100uF capacitor
- 100uF is essential part of the LC circuit network but electrolytic caps are not good at RF, there should have been ceramic cap in parallel with it.
etc.
this is oscillator that should be adjusted to 4.5MHz, how are you measuring voltages? with oscilloscope?