Kacher calculator: Brovin kacher, MOSFET kacher, Slayer exciter
A kacher is a self-oscillating single-transistor oscillator with an air-core coil: the secondary coil sets the frequency, its base end drives the transistor. The tool calculates the coils, the operating frequency and the coupling and shows in tables what other wires, tubes and turn counts do.
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Abbreviations and symbols on this page (12)
- Kacher
- Name given by V. I. Brovin to his self-oscillating single-transistor oscillator with an air-core coil; the base of the secondary coil drives the transistor.
- NPN
- Type of bipolar transistor; switches on when current flows into the base.
- MOSFET
- Metal-Oxide-Semiconductor Field-Effect Transistor: field-effect transistor switched by the voltage at the gate.
- Slayer Exciter
- Very simple Kacher variant with a small-signal transistor, a resistor and an LED, usually powered from 9 V.
- L1, L2
- L1 = primary coil (few turns), L2 = secondary coil (many turns).
- R1, R2, C1
- Resistors that set the transistor's operating point; C1 buffers the supply.
- LED
- Light-emitting diode; in the Slayer Exciter it protects the base against reverse voltage and shows that the circuit is running.
- RF
- Radio frequency: alternating currents and fields from roughly a few tens of kHz; here mostly 50 kHz to a few MHz.
- k
- Coupling coefficient between two coils, 0 to 1: the share of the magnetic field that passes through both coils.
- λ/4
- Quarter of the wavelength λ = c ÷ f (c = speed of light). A secondary coil resonates much like a quarter-wave radiator.
- X(Lp)
- Reactance of the primary coil at the operating frequency: X = 2π f Lp, in ohms.
- Zener diode
- Diode that conducts above a fixed voltage; limits the MOSFET gate voltage.
1. Variant
Three common single-transistor circuits. All oscillate by themselves at the resonance of the secondary coil.
The kacher after V. I. Brovin: a bipolar power transistor, the primary coil at the collector, the base end of the secondary coil at the base. The transistor works in a special oscillation mode (Russian “kacher”), the frequency is usually around 1 MHz.
Bipolar power transistors such as KT805 or KT902 (recommended by the inventor), also KT815, KT819, KT838; heat sink; supply usually 12–30 V from a power supply.
+ simple, few components, frequency sets itself
− transistor gets hot, operating point must be adjusted
- Secondary coil: about 800–1500 turns of 0.1–0.2 mm enamelled wire on a plastic tube with 20–50 mm diameter.
- Aspect ratio (length : diameter) about 4 : 1 to 5 : 1.
- Primary coil: a few turns (about 2–6) of thick wire (1.5 mm or more) around the lower part of the secondary coil, as a cylinder or cone.
- The base end of the secondary coil goes to the base or gate, the top end stays free or gets a small topload.
- If nothing oscillates, swap the primary coil leads: only one direction works.
2. Coils, frequency and coupling
Enter the secondary and primary coil. The drawing is to scale, the animation shows the voltage distribution.
| Operating frequency (resonance of the secondary coil) | 961 kHz |
| Turns | 1066 (66.6 / cm) |
| Aspect ratio (length : diameter) | 4 : 1 |
| Inductance (Lundin) | 10.2 mH |
| Self-capacitance (Medhurst) | 2.69 pF |
| Wire length | 134 m (1.72 × λ/4) |
| Resistance DC / at resonance | 148 Ω / 148 Ω |
| Primary inductance (Wheeler) | 0.878 µH · Ø 6.3 cm · 58 cm conductor |
| Coupling coefficient k | 0.188 |
| Reactance of the primary coil at f | 5.3 Ω |
3. Modifications compared
What happens if you change the wire, tube or primary turns? Click a value to apply it.
| Ø | Turns | L | f | Wire | R |
|---|---|---|---|---|---|
| 1999 | 35.7 mH | 513 kHz | 252 m | 975 Ω | |
| 1600 | 22.9 mH | 641 kHz | 202 m | 500 Ω | |
| 1333 | 15.9 mH | 769 kHz | 168 m | 289 Ω | |
| 1066 | 10.2 mH | 961 kHz | 134 m | 148 Ω | |
| 888 | 7.08 mH | 1.15 MHz | 112 m | 85.7 Ω | |
| 800 | 5.75 mH | 1.28 MHz | 101 m | 62.6 Ω | |
| 640 | 3.69 mH | 1.6 MHz | 80.9 m | 32.1 Ω | |
| 533 | 2.56 mH | 1.91 MHz | 67.5 m | 18.6 Ω |
| Ø | Aspect ratio (length : diameter) | L | f | Wire |
|---|---|---|---|---|
| 8 | 2.7 mH | 2.07 MHz | 67.5 m | |
| 6.4 | 4.15 mH | 1.63 MHz | 84.2 m | |
| 5 | 6.66 mH | 1.24 MHz | 108 m | |
| 4 | 10.2 mH | 961 kHz | 134 m | |
| 3.2 | 15.5 mH | 739 kHz | 168 m | |
| 2.54 | 23.8 mH | 559 kHz | 211 m | |
| 2.13 | 32.8 mH | 450 kHz | 252 m |
| Primary turns | Lp | k | X(Lp) |
|---|---|---|---|
| 0.119 µH | 0.149 | 0.721 Ω | |
| 0.429 µH | 0.168 | 2.59 Ω | |
| 0.878 µH | 0.188 | 5.3 Ω | |
| 1.43 µH | 0.206 | 8.63 Ω | |
| 2.06 µH | 0.225 | 12.4 Ω | |
| 2.75 µH | 0.243 | 16.6 Ω | |
| 4.28 µH | 0.276 | 25.8 Ω |
- Thinner wire: more turns on the same length, higher inductance, lower frequency, but more resistance and heat.
- Larger tube diameter: more inductance and self-capacitance, much lower frequency, longer wire.
- Longer winding: more turns, lower frequency, higher voltage at the top end, but a slimmer coil with looser coupling.
- More primary turns: more inductance and usually tighter coupling; the current through the transistor drops, the excitation becomes weaker.
- Topload (small sphere or ring on top): more capacitance, lower frequency, calmer discharge.
Formula
Same coil formulas as in the Tesla calculator: L after Lundin, self-capacitance after Medhurst, f = 1 ÷ (2π √(L (C_self + C_topload))). Turns = winding length ÷ (wire diameter + spacing), wire length = N π D. Primary after Wheeler (helix, spiral, cone), coupling k = M ÷ √(Lp Ls). Reactance of the primary coil X = 2π f Lp.
Example
Tube 40 mm, 16 cm winding with 0.15 mm enamelled wire: 1066 turns, 134 m of wire, 10 mH, about 0.96 MHz. Primary coil 3 turns of 1.5 mm on 60 mm inner diameter around the base: 0.9 µH, k ≈ 0.19.
Notes
- A kacher's frequency settles by itself at the resonance of the secondary coil; the calculator gives the starting value. A hand, the table and a topload lower it.
- The component data and rules of thumb come from build reports (cxem.net, elquanta.ru, pikabu, Instructables, forums) and partly contradict each other. They are starting values, not a tested recipe.
- If it does not oscillate: swap the primary coil leads. The base end of the secondary coil must be connected to the base or gate.
- The transistor needs a heat sink; the kacher gets hot quickly. Mains-powered versions are life-threatening and only for experienced builders with an isolation transformer.
- RF fields interfere with radio and electronics. Keep away from pacemakers, mobile phones and measuring instruments; never try it on people or animals.