Here's a circuit I'm working on. It's a parametric oscillator that I plan to adapt for use in driving the Drive Coils on the motional-EMF device I'm building. I tried building it with only varactors rather than capacitors, but I couldn't keep it in resonance.

The 4 Drive Coils (portrayed as 13.5 mH inductors) peak out at ~600 mA current at ~11.3 volts, or ~6.8 watts of circulating power per coil.

The 555 timer only takes ~800 uA at 12 volts, or ~10 mW.

The battery supplies ~10 mW of constant current, with very short ~524 mW pulses to the coils.

The varactor acts to keep the voltage pulse from the MOSFET centered at the peak of the waveform.

The zener diode acts as the drain to ground, while maintaining a minimum of ~5.5 volts so the coils ramp up their oscillations more quickly.

The 1 uH inductor is there to ensure both banks of two inductors are balanced and don't 'cross-talk', rather they oscillate in concert with their associated capacitor.

Here's the code for it:

$ 1 0.000005 5.023272298708815 42 10 50
165 224 144 272 144 0 0
w 224 176 192 176 0
r 192 176 192 240 0 474000
w 192 240 224 240 0
w 192 240 192 272 0
w 192 272 224 272 0
w 192 272 192 352 0
c 192 352 192 384 0 5.0000000000000004e-8 0.001
g 192 384 192 400 0
r 192 352 304 352 0 5000
d 352 352 304 352 2 default
w 352 208 352 352 0
f 352 208 400 208 32 1.5 0.02
w 288 112 400 112 0
w 400 112 400 192 0
l 400 256 400 304 0 0.0135 0
c 464 256 464 304 0 0.00052 0.001
w 400 224 400 240 0
w 400 304 464 304 0
c 288 304 256 320 0 1e-11 0.001
g 256 320 240 320 0
w 400 192 416 192 0
d 416 240 416 192 2 default
v 448 112 400 112 0 0 40 12 0 0 0.5
g 448 112 448 128 0
l 400 304 400 352 0 0.0135 0
c 464 304 464 352 0 0.00052 0.001
w 400 352 464 352 0
w 528 352 592 352 0
c 528 304 528 352 0 0.00052 0.001
l 592 304 592 352 0 0.0135 0
w 528 256 592 256 0
g 656 352 672 352 0
w 528 304 592 304 0
c 528 256 528 304 0 0.00052 0.001
l 592 256 592 304 0 0.0135 0
w 464 256 528 256 0
l 464 352 528 352 0 0.000001 0
w 416 240 400 240 0
176 656 256 592 256 2 default 0 6.9e-11
w 656 304 656 256 0
O 464 240 512 224 0
w 656 352 656 304 0
w 416 240 448 240 0
w 416 192 448 192 0
c 448 192 448 240 0 1e-11 0.001
w 464 240 448 240 0
w 400 240 400 256 0
w 400 256 464 256 0
z 656 352 592 352 2 default-zener
o 15 64 0 12553 0.0001 0.0001 0 2 15 3
o 25 64 0 12553 0.0001 0.0001 1 2 25 3
o 35 64 0 12553 0.0001 0.0001 2 2 35 3
o 30 64 0 12553 0.0001 0.0001 3 2 30 3
o 23 64 1 28931 0.0001 0.0001 4 1 0.0001
o 41 64 0 12546 0.0001 0.0001 5 1
o 32 64 0 12545 0.0001 0.0001 6 2 32 3

You can go here (Falstad Circuit Emulator) and click on the 'File' link, then click 'Import From Text'.

If I've made any mistakes on the circuit, or you have any improvements, let me know.