I'm trying to make a simple circuit

[Hypercase]

I'm trying to make a simple circuit. The circuit design says that i need to use a 3-18 pf adjustable capacitor, i haven't been able to obtain that component.
Could you please suggest a replacement that would work just as well as the 3-18 pf adjustable cap.

 

[Averagesupernova]

A 3 to 18 pF cap is a 3 to 18 pF cap. No replacement. Although, you could use a 3 to 25 or 30 or something. You just will not use up all of the range of the cap before you reach 18 pF and will have poorer resolution.

You might try adding in series a cap if you like to change the value of the variable cap. Caps in series inversely add. 1/c1 + 1/c2 = 1/ctotal.

 

[brewnog]

I quickly found a 3.5 - 20pF on RS, stock number 125-963. Keep looking and you might just find what you need.