How to detect Resonance?
A relative low cost device to check resonant circuits is what used to be called a grid dip meter because it measured the grid current in a vacuum tube oscillator circuit.  When the coil of the oscillator is placed close to a resonant circuit, and the oscillator is tuned to the resonant frequency of that circuit, the resonant circuit will draw power from the oscillator and cause a lowering (dip) of the grid current.  Grid dip meters were constructed so that the inductor was external to the meter and could be easily coupled to a another circuit and also could be interchanged to allow a wide tuning range.  Newer versions used a transistor oscillator instead of a vacuum tube but the principle remains the same.  These meters typically covered a range from about 100 kHz up to 250 MHz and were calibrated with an accuracy of a few percent.  They were made by companies such as Eico, Heathkit, Miller and Kenwood.  You should be able to obtain one at a very reasonable price on Ebay.