Hey,
I’ve been working for a couple of days on the super simple oscillator, the circuit seems to be correct but I can’ t hear any audio :/. Before, when the circuit was incorrect, there was a steady electronic noise that seemed to be the result of the oscillator+the noise from the mixer; I also noticed that when I touched certain legs of certain components either with the tweezers or my hand, the noise amplitude was raised Sensibly. Now this noise disappeared and I can’ t hear anything. The +V is provided from 2 9v batteries connected in series, and the GND is the - side of the battery. The led glows and its intensity is responding to the potentiometer movement. I also checked with the multimeter in continuity mode and everything seems to be all right. Here’ s the picture of my breadboard layout.
Hope that u guys can help me!
Have you tried a different transistor? I’ve heard some 2N3904s work and some don’t although all the ones I’ve tried do. Also, you say the circuit was “incorrect” before; could you have blown the transistor? I don’t see any obvious problem in your photo. Though not seeing the obvious is one of my superpowers. The resistor in series on the output looks like it’s seen better days, maybe try swapping that?
Yeah actually the resistor is quite new, I just scratched the surface trying to change it’ s position. I have a bunch of different transistors here, I’ ll try now with a 2N3906
No, that won’t work, 2N3906 is PNP.
At this point I’ m thinking that the problem is in the jack socket, could it be?
One thing to try is a different 2N3904. As I said, reportedly some work and some don’t. I don’t know if it varies depending on the batch or the maker or piece to piece or what — the ones I’ve tried have worked.
Also: BJT In Reverse Avalanche Mode – Kerry D. Wong
Oh yeah, ALWAYS look suspiciously on your wires and connectors! Remember the faster than light neutrinos? Bad connection.
Well eheh! I tried replacing the transistor with another one of the same type but it’ s not working either. I also tried to change the capacitor with a much bigger one (100 uF) but still no sound (I thought that maybe the frequency of the oscillation was too slow to even hear it). Also, my led it getting brighter and dimmer according to the position of the potentiometer dial: is it correct or should it blink following the oscillation rate?
I’ m quite confident that the jack socket works, since I hear crackling in the headphones as I connect the alligator clips to the socket’ s pins. I also tried to try the same alligator clips on different pins, with no positive result 
A few threads have discussed problems with this Circuit. Not sure if its because its usually people’s first or that really this reverse avalanche effect that causes the oscillation isnt as consistent as people expect. I skipped building this thing, so i cant say i have any experience with this one.
Do you have a multimeter? If se, we can guide you in the process of troubleshooting if you like. Also, are you using new batteries?
Hey @Caustic ,
I do have a multimeter, it would be super nice if u could help me with the troubleshooting!!
Bigger capacitor will make the frequency lower, not higher. But 10 to 100 uF should be audible. If there’s oscillation it will be too rapid to see the LED flashing, but yes, the brightness will change with the pot setting. Check your connections from the transistor to the resistor to the jack and from the jack to ground.
I also read these posts already, in fact I layed out the component on the Breadboard as @richy486 did in his latest posts and discovered some errors in my previous circuit. So it was very helpful
Oh yes sorry you are completely right!
@Caustic so I tried to change the transistor with a S9014 first and a S9018 later, which are other transistros that appear on Kerry Wong’s website, but still no sound. I checked the circuit again and again and everything seems to be working. I also watched this video https://www.youtube.com/watch?v=wRBB7lsQ7o4, which seems to bring up more problems, such as that the volume is very low and stuff. I had tought before that the problem could be related to the volume, but when I’m using headphones directly in the jack socket, I don’t hear sound at all; when I plug the oscillator into my mixer, I get only the noise from the mixer. At this point I’m quite confused
Did you disconnect power before continuity checking? These sorts of breadboards sometimes split halfway, but i think you have avoided any problems with that.
@Caustic thanks for the very detailed explanation! It will help for sure! Tomorrow I’ ll check if I have different avalanche transistors and I’ ll let u know. I’ m quite confident that with a bit of more work and some more good advices I’ ll get this to work and complete my first DIY project!!! Hope that u guys will be here for some more help 
well the way the continuity works is it sends a bit of power and checks if the circuit is complete that way. if it is already powered, you arnt doing the test right. If you get power, that probably means there isnt a break anyways so its prolly fine. Just know its best to test with power off.
Also, are we sure those resistor values are correct? Its a bit hard for me to see the colors.