At first I tried to run it using 5v but could not reach a 170v output, so I opted for a 12V supply and put in an LM7809 regulator. I put a heatsink on it although it probably does not need one. I was able to get 170V but found that this would change if I varied the input voltage (bypassing the 9V regulator that is) But the main issue is that the voltage drops if I connect a load.
No load: I/P = 12V @ 100mA; O/P = 170V @ 0mA
1 neon load: I/P = 12V @ 200mA; O/P = 148V @ 0.82mA
2 neon load: I/P = 12V @ 200mA; O/P = 133V @ 1.3mA
Testing with 1 neon load: By adjusting the variable resistor I can reduce the voltage, but cannot get it above 148V. It is as if my circuit is reaching saturation. I had triggering issues on my scope but noticed that the square wave did change from no load to 1 neon load, but adding the 2nd neon did not "seem" to make a difference.
I checked the electrolytics = ok. Coil = 100uH. The 1k & 2K2 resistors were swapped around, but that made no difference. I even replaced the 555. I may have used an IN4004 diode instead of a UF4004 - is there a difference? Checked for shorts, parts placement,.......
I did order a ready made supply which is currently on a slow boat from China, but would prefer to use my own build anyway. Although I did get the schematic off the net. Any ideas where I failed or what I else I could test for? Any help would be appreciated.
Thank you for the feedback.
I will try to answer as many quetions as I can.
Neon tubes don't use much current, so I should be ok with the 12V 2A supply I intend to use. (tetsted with 4A bench supply)
Why a 555? Probably because I'm a bit nostalgic about these and because I had quite a few lying around.
(@Finbarr) I originally put in a 9V regulator because the output voltage would vary with the input voltage and I wanted a stable output. If this issue is resolved once I get the circuit going, then I will remove it. I want to protect my precious Nixi tubes just in case I (or someone else) plugs in the wrong power supply. And then I read your next reply about the input voltage varying the frequency and duty cycle, so it looks like the 9v regualtor stays.
I used a 350V rated cap on the output.
I remember that component prfixes used to be manufacture specific, so TI would have a different prefix than Fairchild......
But I started to think about the diode more and more. Thank you for confirming this and I will pop off to the local elecronics supplier and pick up a UF4004. Fingers crossed!