oh.. That P.O.S. schematic!
The dumbass that published it should be hooked up to the correct version of it and fried for a few minutes! I have seen this one countless times!
Or one so close to it I cant tell the difference from memory.
I have done several dozen 6 volt to 12 electrical conversions on tractors, trucks, old viehicals and assorted farm machinery over the years. I often put a 4 ohm 10 watt resistor between the 12 volt source and the coil if I dont have a internal resistor type coil available. To greatly help out the "inductive snap" put the capacitor parallel to the switching transistor.
This is how the old points and condensor ignition systems are set up. Most of the condensors I have checked over the years run anywhere from around 2 uf to as much as 20 uf. most are in the 2 to 6 uf range.
Use an old condensor from a lawn mower or some old points type ignition system if you have one available. Mylar non polars work great too. just make sure they have 200 volt or higher rating. Playing with the capacitor value will help you tune it to get the best sparks.
I would put a diode in the line feeding all the 555 control stuff with a capacitor on the 555 side.
This blocks reverse voltage spikes and helps isolate the controls from the 12 volt power. I would also put a diode and capacitor across the whole switching end too from the input of the coil to the output of the switching transistor. This gives a bypass path for the inductance snap to follow and lets the coil and condensor power have a good path to follow when they resonate.
And definitely toss the 2N3055 transistor and use a Mosfet or IGBT or at least a high gain darlington with a 200 volt 10 amp or higher rating!
um... turn the coil around. If your using the schematic shown your firing it the wrong way! wierd as it may sound this helps alot on this circuit.
The primary of the coil is in series with the secondary not parallel as most seem to think.
When properly done this circiut can blow sparks right out the top of some coils outputs and back down to the side terminals!
Just like in the picture I posted earlier! Thats one of my spark toys. I am running back to back coils one is forward firing the other is reverse firing. (180 degrees out of phase) I have 6 volt coils with 24 volt sources and no resistors.
the switches are 600 volt 50 amp IGBT's and the circuit is set up for adjustable dwell (Switch ON/OFF time) and frequency! Very tunable and can vary the spark size and intensity greatly!
Once you have your sparker set up and working properly feed an audio signal into pin 5 on the 555. If done properly your sparker will sing for you!