Hi all!

I am asking for help if someone, may be @FrontSideBus can measure an inductor used in a real SX72 SOX ignitor.

I am trying to make a replica, tried a wild guess of using an inductor from 36W HF ballast, the circuit does oscillate, but peak voltage generated is on a low side, ~450V so not enough to start my SOX lamp.

Also a a real marking (voltage rating) of MOV (varistor) element in the circuit will be interesting.

Here is a picture of what I am trying.

I'll have to dig one out and have a look.

A quick non-destructive way to measure the coil is to bang it with a charged capacitor and measure oscillation frequency. You can do this right in circuit, as non-conducting TRIAC will isolate the coil from most other components, no desoldering needed. Most competent multimeters can measure capacitors until they are not especially small.

1. Hook an oscilloscope in one-shot mode over the coil terminals.
2. Charge some known verified film capacitor, I had 0.01 uF on hand for example, to some suitable voltage, say 9v.
3. Firmly touch coil terminals with the capacitor.

Then you can calculate the inductance of the coil as L=1/((2*pi*F)^2 *C)

I would like to know the coil DC resistance, too.

Here I captured that damped ringing with 0.01 uF cap. This gives oscillation frequency of about 28kHz, which calculates coil inductance of about 3.2mH which is close to what I exect.

My cheap LCR meter says the coil is 380 mili henrys.
Seems a bit much but the meter reads correct when presented with 22 and 100 micro henry inductors that I had lying about.
DC resistance was 10.7 ohms.

MOV is rated at 1kv.

380mH seems to me as way too much for such small coil. The 3..4mH seems more reasonable value.

Be careful with the generic RLC meters, they can mislead when the coil parameters deviate from what they were intended for.
It is i portant to always be aware what and how exactly the RLC meter works and how it comes to the number it is showing.
If it is some pulse ramp measurement (then what is the timing and impedances), harmonic impedance measurement (then what is the frequency and circuit impedances, how it calculates the inductance, whether it uses parallel or series loss resistor model,...).
Mainly parasitics may skew the result a lot...

My cheap LCR meter says the coil is 380 mili henrys.
Seems a bit much but the meter reads correct when presented with 22 and 100 micro henry inductors that I had lying about.
DC resistance was 10.7 ohms.

MOV is rated at 1kv.

Thanks Mark!

I will try some significantly larger inductance in the circuit and see how it works out.

I'd say 380mH looks a bit high for that purpose, yes and that probably means a coil without a gap. I bet a coil with such inductance and such size of ferrite core will saturate at about 200 milliamps in this circuit, but this may be a part of the game. Hard to say without probing the actual circuit in the work.

By the way, can you still try a capacitor discharge way to directly measure the inductance? Also it will be great if you can hook this SX72 on some suitable ballast choke and capture the actual pulses it generates with an oscilloscope. A 1:100 2kV probe will be enough for this.

I'll try this weekend.