Ok i've tried the schematic you sent me, it gave a nice oscillation, but the frequency was wrong! It had a frequency of about 4.90kHz, whereas it should be closer to 33.93 kHz. Any ideas what the reason of this could be?
I was using a BC337 npn bjt transistor and a 1n5255b zener diode (which i hope is a good stand-in to the diode you were using since i didn't hava any on hand).
The voltage was still +7v and the cap and coil values are the same. The base resistor was the same you were using, 1k.
The images are respectively using the following resistors:
10k
1k
560
220
Are you sure about the component values? I agree, your 10mH / 2.2nF tank should resonate around 33.9 KHz.
The frequency of the ringing tank circuit will only be affected by the values of L and C, and any stray reactance in the circuit. The zener you used has a reasonable low capacitance when reverse-biased, and even if you removed it from the circuit the tank ringing frequency will be virtually unchanged. Your transistor is a fine choice for this circuit (as long as the ringing voltage doesn't exceed the Vce breakdown voltage, which it doesn't). The transistor output capacitance is about 15pF, which is trivial here given the 2.2nF tank capacitor.
I notice in your previous post you also show a 4.9 KHz tank oscillation frequency. I suspect that your inductor is not really 10mH, or possibly the capacitor is not 2.2nF (or both).
Another interesting thing is that your ringing tank voltage is much smaller than I get in my simulation (with a 1K series resistor I get 20V P-P but you get about 3.7V P-P). Can you measure the DC resistance of your inductor? In my simulation I have the inductor resistance at 100 Ohms, which is pretty high for a 10mH part.
Finally, in your previous schematics you show "DSO", which I assume is your digital storage oscilloscope connected directly across the tank circuit. Is this a differential measurement? The top of the tank is at +7V so I hope your scope ground isn't connected there. The fact that the tank voltage goes negative when the transistor switches off tells me that the +7V rail is your ground reference. I don't see how this will affect the resonant frequency, but it might be simpler to measure the tank signal relative to DC ground. There will of course be a +7V offset.