Above you said
but then you said
So you get audio from the individual oscillators but not when connected to the mixer?
Not sure why that would happen but maybe it’s a DC level thing even with single oscillators. So maybe AC coupling will be the fix.
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And maybe you could try by focusing on getting a single oscillator to work to your liking, you can solder capacitor in parallel to “add” their values, so it should be easy to test different combinations
To me it sounds like you’re almost making the 2002 circle drone project, but without the premade PCB. My suggestion would be to look at the schematic posted on this page:
I used this schematic to make my own modified drone with switching capacitors to make 1 circuit have multiple capacitor frequencies in it. I haven’t run into any problems when using the components and schematic listed there. The other piece of advice I can give is 2 things:
- I highly recommend starting out with a breadboard for these kind of projects because it lets you test a circuit fully before spending the time soldering a problematic circuit. It also lets you switch out components quickly so that you can see what could be wrong.
- with the simple oscillator using an ss9018 I find the capacitor stops the reverse Avalanche below a certain voltage and a certain uf capacitor. To me 100uf is much to large, I found after about 40uf the oscillator just stops. You can increase the voltage of the circuit up to about 22v before you run into issues, but increasing the voltage basically just makes the capacitor behave like a lower uf capacitor, which is pointless.
Hope this helps some how!
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Thanks for your patience everyone.
I am making progress. I took it all apart and started focusing on one at a time. I discovered that on a couple of them the transistor was just bad. On some the LED (i had a different color for each cap value) seemed to be causing problems. On those, the LED would light, but no oscillation was happening. I replaced those with a large red LED and that seemed to get things humming along nicely. After swapping out these components, I now have 5 fully INDIVIDUALLY functioning oscillators. My task today will be to wire it all up into my mixer circuit and see what happens.
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Different color LEDs have different amounts of voltage drop (forward voltage) across them — usually higher for blue and green than for red and yellow. That might alter the voltage required for oscillation, or I guess conceivably could prevent oscillation entirely.
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100uf (and 47uf) actually worked well for me at 12v but after getting my oscillators working I wasn’t happy with how it sounded so I’m probably going to stick with 10-22uf going forward.
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Yeah, I thought i’d be okay sticking with red/yellow/orange. Interestingly it was the reds that caused an issue, and replacing them with larger reds fixed it.
Science isn’t an exact science.
I had issues with higher uf value caps as well. Keeping it under 22uf worked for me. Also, you will find you have issues with the passive mix circuit on the circle Drone. Use the opamp dual power mixer. Also, you may need to ac couple your individual outputs.
Don’t sweat it. I know you’ve said you’ve read the other threads on troubleshooting this, but really the oscillation from these is hit or miss. Even if you ultimately dont get these working there are so many other projects that, ironically are much more simple to get working. Its “simple” in terms of components, but in my exp its not so simple for everyone to get it to work. 
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Working out why it’s failing and making it work is a great learning exercise though. I likely won’t get much use from these in the long run but the time will still be well spent
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Just one last update: it’s working 100% now after putting caps between each output and the mixer. I think I might also put a small resistor in parallel with each pot to try and mitigate the dead space at the end.
My (maybe?) last plan is to find a filter circuit to put after the mixer and experiment with that.
Thank you all so much!
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If you’re looking to filter the oscillator, I used the video by Moritz Klein on filters to figure out where to stick a filter into the circuit. It worked pretty well, you can get a very basic low pass filter into the circuit without needing to modify anything really. I just put the filter after the oscillator circuit and before the output/mixer circuit. Highly recommend all of his videos!