Hello,
 I have not experimented in a while with my partially built tesla coil, but
has anyone used their Tesla coil as an antenna for ELF or other Freqs? If we
try to use it for 137 KHz how do you determine ERP?

 I had one I was building a few years ago using a 555 timer as an
oscillator with a buffer. Followed by a Darlington pair diving a pair of
power transistors. never got past the primary coil, due to frying the
primary wire with too much current (i.e. too small of a current limiting
resister and too much drive).