I had salvaged a neon bulb from a soldering iron and wanted to use it in some circuit. I remembered that a bulb is used in Wien bridge oscillator when i wrote about building the wien bridge oscillator calculator and wondered whether the neon bulb of a soldering iron(see repairing soldering iron) could be used in wien bridge oscillator.
Yes, you can use a neon bulb salvaged from a soldering iron indicator in a Wien bridge oscillator, but with important conditions and limitations:
✅ Neon Bulb Basics
Most small neon bulbs (like NE-2, commonly found in soldering iron indicators) have these specs:
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Breakdown (striking) voltage: ~60–90 V
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Maintaining voltage: ~50–60 V
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Current: Very low (~0.1 to 2 mA)
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Polarity: Non-polar (can conduct AC)
⚠️ Key Considerations
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Supply Voltage:
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Neon bulbs require at least 60V to turn on.
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If your Wien Bridge Oscillator circuit runs on low voltage (e.g., 12V or 15V op-amps), the neon bulb won't conduct, and won’t regulate amplitude.
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It's suitable only if your oscillator operates at a high enough voltage.
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Circuit Role:
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The bulb is usually placed in parallel with a resistor in the gain-setting feedback network.
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When the amplitude increases too much, the neon strikes and lowers gain — providing nonlinear feedback to stabilize amplitude.
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Aging and Reliability:
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Salvaged bulbs may be aged or degraded. If they no longer light up or strike reliably, they won’t work effectively.
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Test the bulb beforehand by connecting it through a 100k resistor to ~100V AC or DC.
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✅ Conclusion:
Yes, you can use a salvaged neon bulb from a soldering iron in a Wien bridge oscillator if your circuit voltage is high enough (around or above 90V), and the bulb is still functional.
