Notes:
The original data sheet for the ZN414 states that the maximum working frequency is around 4 MHz. That may be
true, but SW broadcasts are so powerful that this receiver will work well with signals up to around 6 or 7 mhz.
The 10k resistor controls the operating voltage for the ic which is critical for good performance.

The tuned circuit consists of a variable capacitor and fixed air spaced coil. For the inductor, I wound 10 -20 turns
of wire on an empty tube of around 1.5 inches diameter. The turns were spaced so that the overall length was
around 3 inches. The variable capacitor tuned 0 - 300 pF but there is plenty of scope for experiment here. One
final point, you will need an external antenna to receive broadcasts. I have an outside wire that is about 7 meters
long and this was quite effective. The antenna can be connected at either end of the coil or via a series capacitor
value between 10pF and 100 pF.