[Amps] Square plate choke ?

[k7fm]

Old crystal sets used to be wound on square wood.  It made it easier to 
scrape the insulation off for tuning.

You need not figure out the formula.  Just build one and measure the 
inductance and resonance points.  Even better if you have a network 
analyzer, but crude equipment will give you enough information.

Square stock is a lot tougher to groove, though, so you will have to be 
satisfied with close wound wire.

For show, you might try triangular, too.

73,  Colin  K7FM