No,
no diode needed.
Just measure first the voltage from this additional coil
on the scope and see, which amplitude is higher,
the positive or the negative and then use the higher amplitude
for the positive side.
So in other words, just find the right polarity to pulse it through
the sparkgap onto the battery.

On my SSG I have a separate tri-filar power coil wound alongside the bi-filer trigger-power and there I only get ~200V spikes which appears not sufficient for this spark-gap I made because nothing happens.

I suppose the electrodes needs to be even closer for these low voltages, or I'm not doing something right...

Yes, 200 Volts is a bit low.
You need at least I would say 500 Volts or you need to cut
the rods into needle sharp like tips !
If you make them needle shaped at the end, there
the electric fields are much more dense and thus
the spark will jump much easier !

I was able to squeeze 400V out with a fresh battery and get the micro spark-gap to work, sort of.

I followed Stefan's advice and sharpened the ends to a needle point and when plugged into the circuit had to push one end of the electrodes to create a momentary contact and then it would spark. Suffice to say it does not smell nice.

Turns out the electrodes in the micro spark-gap have to be *really* close, much closer than I thought. Also, because my wire was wrapped around the electrodes and then electrodes glued to the plexiglass with hot glue gun, it started sparking where my wire was wrapped around on one electrode. As a consequence, it was getting hotter around that area and the glue started to melt. Talk about a chain reaction, hehe.

I can see the potential in the spark gap, but we need voltages in excess of 1000V to be able to use a spark gap of nominal size and not something super miniature.

This also makes me wonder about something else, a multi-filar circuit where one coil is a start-up driver, using conventional pulse electronics to kick start the self oscillations. Post start-up set of driver coils wired via a spark gap to a large high voltage capacitor(s) to continue the process. Last set of coils would be power coils used for whatever output is deemed necessary.

Of course that post start-up driver set of coils would need to produce 1kV and above, and be tuned properly with the right capacitor(s) and the spark gap so that the oscillations continue and do not stop. Definitely out of my reach of experimentation, for the time being anyway.

Hi

I was usually using a car ignition coil but they consume a lot of power and these type of coils can make big sparks.
So i was looking for a methode to produce high voltage with not too much input and i found some old backlight inverters used in laptops.
These you can just pulse with a signal generator to get high voltage out.
The primary is wound as two coils so it's also possible to use one for the drive and the other for the trigger in a blocking oscillator setup.
Then you can adjust the frequency just by bringing a magnet close to the core.
Another way is to pulse a coil which has many turns of fine wire and connect the signal generator in a way that only the pulse can go into the coil ,but not out of it into the signal generator.
Then you use two other diodes connected in reverse so that they only let the pulse out of the coil to collect the high voltage spike which is caused right after the Bemf due to extremly rapid collapsing of the field.
Basicly the circuits i have tested have had 5 elements.
1.a signal source.
2.a step up item.
3.wires of equal lengths and a means to guide the flow in and out of the coils and sometimes capacitors too.
4.the spark gap.
5.offcource is the output element, which mostly was NE2 bulbs but other things were used too.

M.