Electron-coupled oscillator

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An electron-coupled oscillator (ECO) is a vacuum-tube circuit used in radios. It uses a screen-grid tube where the cathode, control grid, and screen grid form the oscillator, while the plate sits in the output circuit and is shielded from the oscillator by the screen grid. The ECO remains stable even if the load changes a lot. Temperature changes in the heater-cathode capacitance help offset other temperature effects, so the oscillator’s frequency drift during warm-up is smaller than in many other tube circuits. The ECO was used in shortwave superheterodyne radios.