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A simple Tesla music coil

patrykkurzejago 10806 32

TL;DR

  • A simple musical Tesla coil was rebuilt from a single-transistor design so it could play tunes instead of only lighting fluorescent lamps.
  • The primary was changed to 5 turns, the secondary to about 1000 turns on a 5 cm PVC pipe, and a yellow LED plus a second transistor improved robustness.
  • The coil ran at 30 V and about 30 W using a LRS-100-36 supply reduced from 36 V.
  • An ESP8266 generated square waves to drive a 2N7000, shorting the transistor bases to ground and making the coil play simple tunes.
  • The circuit was only temporarily soldered on a universal board, and the author notes the schematic still has shortcomings.
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  • #31 20816932
    patrykkurzejago
    Level 6  
    Posts: 8
    Rate: 33
    A slight dig, but today I tested for myself what happens when touched. Of course, not specifically, however, it happened. I'm alive, I didn't feel the current, but it burned a 2 mm hole in my hand to a depth of about 0.5 cm. Pain, the stench of burning skin and nothing pleasant, but I'm alive ;P It's better to touch a heated soldering iron, the pain is the same, but the damage is less. I found that I will share this with you, because it was one of the main topics of discussion in this thread.
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  • #32 20817245
    _lazor_
    VIP Meritorious for electroda.pl  
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    I am sorry that the accident happened, at the same time thank you for sharing your experience
  • #33 20817539
    KJ
    Level 31  
    Posts: 2370
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    Well, yes high-frequency electrocution usually resembles the effects of a burn more than what is usually associated with the effects of paralysis. Plus it heals nastily.
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Topic summary

✨ The discussion revolves around building a simple musical Tesla coil, with the original poster sharing their experience of modifying a single transistor-based design to produce sound. Initial attempts resulted in poor performance, prompting adjustments to the winding configuration, which improved spark generation but led to transistor failures. Participants suggested checking the operating frequency, as Tesla coils function as radio transmitters, and discussed the importance of tuning the resonant frequency through inductance and capacitance. The use of an SDR (Software Defined Radio) was proposed to detect the coil's frequency, which was found to be around 1.037 MHz during testing. Safety concerns regarding electromagnetic fields and the potential dangers of high-voltage discharges were also highlighted, with warnings about the risks to individuals with heart conditions. The conversation included technical insights on resonant circuits, the epidermal effect, and the generation of ozone and nitrogen oxides during operation.
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FAQ

TL;DR: A 30 W, 1.037 MHz musical Tesla coil proves that “Tesla coil is essentially a radio transmitter” [Elektroda, bambus94, post #20144574] while remaining buildable with two BD239 transistors [Elektroda, patrykkurzejago, post #20144206] Safe handling and proper tuning are critical. Why it matters: Even small coils can burn skin, jam Wi-Fi and broadcast unintended RF.

Quick Facts

• Resonant frequency: 1.037 MHz detected with RTL-SDR [Elektroda, patrykkurzejago, post #20144646] • Supply: 30 V DC from trimmed 36 V SMPS [Elektroda, patrykkurzejago, post #20144206] • Output power: ≈30 W at 1 A [Elektroda, patrykkurzejago, post #20144206] • Windings: Primary 5 turns / 1.5 mm; Secondary ≈1000 turns / 0.25 mm [Elektroda, patrykkurzejago, post #20144206] • SDR coverage 0.1 MHz–1.7 GHz with R820T2 tuner [Elektroda, patrykkurzejago, post #20144595]

1. What schematic was the starting point for this build?

The author began with a single-transistor SSTC diagram found online, then redrew it to use two BD239 NPN transistors, an LED across the bases and an ESP8266 audio gate [Elektroda, patrykkurzejago, post #20144206]

2. Which modifications increased spark length?

Increasing primary turns from 3 → 5, raising supply to 30 V and adding ~1000 secondary turns boosted spark visibility and lamp excitation [Elektroda, patrykkurzejago, post #20144206]

4. How does the coil play music?

An ESP8266 outputs a square-wave melody; a 2N7000 FET grounds the transistor bases rhythmically, amplitude-modulating the RF and producing audible plasma tones [Elektroda, patrykkurzejago, post #20144206]

5. How can I measure resonance without an oscilloscope?

Use an RTL-SDR dongle: the coil radiates; tune from 0.5–5 MHz until you see a strong peak (1.037 MHz in this project) [Elektroda, patrykkurzejago, post #20144646] Alternatively, compute f ≈ 1 / (2π√LC) with online calculators when L and C are known.

7. What effects on nearby electronics were observed?

Google Nest speakers in the next room randomly changed volume; fluorescent lamps lit from ≥30 cm; smart-band and phone survived close passes [Elektroda, patrykkurzejago, post #20146027]

8. Can I raise the supply voltage for bigger arcs?

Yes, but transistor heating rises with frequency. Users report safe operation up to 30 V; beyond that, core losses and transistor SOA limit apply [Elektroda, patrykkurzejago, post #20144206]

9. How do I tune a Tesla coil efficiently?

  1. Wind secondary first and calculate its self-resonance. 2. Start with extra primary turns. 3. Slide an alligator clip to vary inductance until spark length maximises and transistor heat minimises [Elektroda, rosomak19, post #20147034]

10. What is the wavelength-equals-wire-length debate?

Some hobbyists aim for secondary wire length ≈ ½ λ; others focus solely on LC resonance. Experts note performance depends on L and C, not wire length alone [Elektroda, Janusz_kk, post #20145799]

11. Which gases form around the arc?

Ozone and nitrogen oxides form; litmus paper turned red near the arc, confirming NOx presence [Elektroda, patrykkurzejago, post #20147860] Prolonged exposure above 0.1 ppm ozone irritates lungs [EPA, 2023].

12. What primary and secondary wires work best?

Use 1–2 mm² copper for the primary to handle currents; 0.2–0.3 mm enamelled magnet wire suits a 25 cm secondary, giving ≈1000 turns [Elektroda, patrykkurzejago, post #20144206]

13. How can I reduce transistor heating?

Lower resonance by adding a toroid or increasing secondary height; reduced frequency cuts switching losses. Ensure a heat-sink keeps case <70 °C [Elektroda, Janusz_kk, post #20145799]

14. What myths surround the skin effect?

High-frequency current still penetrates tissues because the body is ionic and inhomogeneous; skin effect does not guarantee safety, especially in DRSSTC class where peak discharge current can reach amps [Elektroda, KJ, post #20162812]

15. 3-step: Measure frequency with RTL-SDR

  1. Power the coil a short distance from the antenna.
  2. Open SDR software, set range 0.5–5 MHz, gain low.
  3. Identify the strongest peak (e.g., 1.037 MHz) and note harmonics. [Elektroda, patrykkurzejago, post #20144646]
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