The Seiler oscillator is an LC

electronic oscillator An electronic oscillator is an electronic circuit that produces a periodic, oscillation, oscillating electronic signal, often a sine wave or a square wave or a triangle wave. Oscillation, Oscillators convert direct current (DC) from a power supp ...

. It was presented in 1941 by E. O. Seiler. The original implementation used a vacuum tube in an

Electron-coupled oscillator In the vacuum-tube radio, an electron-coupled oscillator or ECO oscillator uses a screen-grid tube with the cathode (vacuum tube), cathode, control grid and screen grid forming the elements of the frequency-generating circuit while the plate is ...

circuit. Like the

Clapp oscillator The Clapp oscillator or Gouriet oscillator is an LC electronic oscillator that uses a particular combination of an inductor and three capacitors to set the oscillator's frequency. LC oscillators use a transistor (or vacuum tube or other gain el ...

and the

Vackář oscillator A Vackář oscillator is a wide range variable frequency oscillator (VFO) which has a near constant output amplitude over its frequency range. It is similar to a Colpitts oscillator or a Clapp oscillator, but those designs do not have a constan ...

it is a variation of the Colpitts oscillator. It uses a voltage divider made of two capacitors, named C3 and C4 in the original schematic. The tuning capacitor C1 is parallel to the inductance L1 of the LC circuit. In an Clapp oscillator, the tuning capacitor is in series to the inductance. The variable capacitor C2 controls the coupling between the tube and tank (LC circuit).

Practical example

The schematic shows an example with component values.The Seiler oscillator uses a LC circuit L1, C1 that is connected via C2 to a capacitive voltage divider C3, C4 that connects to the amplifier Q1. C1 and C2 are calculated for inductance L1 having a unloaded

Q factor In physics and engineering, the quality factor or ''Q'' factor is a dimensionless parameter that describes how underdamped an oscillator or resonator is. It is defined as the ratio of the initial energy stored in the resonator to the energy los ...

of 250. Resistor R1 sets the collector current to 0.5mA with no oscillation. The negative supply voltage V2 allows direct connection from Q1 base to ground. The radio frequency choke L3 is needed to isolate the LC circuit from the power supply, but has a potential problem. L3, C3 and C4 create a Colpitts oscillator circuit. R2 reduces the Q factor of L3 and prevents oscillation on the wrong frequency. The correct oscillator frequency is 10MHz. The load resistor RL is part of the simulation, not part of the circuit.

References

Sources

* {{cite book , last=Gottlieb , first=I. , title=Practical Oscillator Handbook , publisher=Elsevier Science , year=1997 , isbn=978-0-08-053938-6 , url=https://books.google.com/books?id=e_oZ69GAuxAC&pg=PA182 , access-date=2024-05-10 , pages=182-183 Electronic oscillators Electronic design