Grid bias


Grid bias

Grid bias is a DC voltage applied to electron tubes (or valves in British English) with three electrodes or more, such as triodes. The control grid (usually the first grid) of these devices is used to control the electron flow from the heated cathode to the positively charged anode. Bias point in small-signal applications is set to minimize distortion and achieve sufficiently low power draw. In high-power applications, biasing is typically set for maximum available output power or voltage, with a secondary target of "either" low distortion "or" high efficiency.

* In a typical voltage amplifier, including power stages of most audio power amplifiers, DC bias voltage is negative relative to cathode potential. Instant grid voltage (sum of DC bias and AC input signal) should never rise above cathode potential to prevent grid-to-cathode currents that overload preceding amplifier stages and may cause severe even-order distortion. High transconductance tubes develop significant grid currents even with small negative bias; in these cases, maximum instant voltage ceiling is lowered to -1.0..-0.5 Volt.
* High efficiency Class B+ push-pull amplifiers operate at higher bias points (near zero or even positive values). These designs take care of grid currents through the use of cathode followers or interstage transformers easing current load on the driver stages, and deep negative feedback to minimize distortion.
* High power transmitter tubes (oscillators and modulators) are frequently positively biased to maximize radio frequency output. Distortion is minimized by using band-pass filter loads tuned to the desired radio frequency.

Bias voltage is obtained through:
* An external voltage source (fixed bias) - a battery or a dedicated DC power supply. When the cathode potential is raised above ground (as in cascode circuits), bias voltage is obtained by tapping into main (positive) plate power supply.
* Automatic bias - using a cathode resistor to raise cathode potential above grid (tied to ground) and stabilize plate current;
* Grid leak bias - diverting DC grid current through a high value grid resistor.

ee also

* Biasing


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • grid bias — n. a steady, direct current voltage applied to the control grid of an electron tube to make it negative with respect to the cathode …   English World dictionary

  • grid bias — tinklelio priešįtampis statusas T sritis fizika atitikmenys: angl. grid bias; grid bias voltage vok. Gittervorspannung, f rus. напряжение сеточного смещения, f pranc. polarisation de grille, f …   Fizikos terminų žodynas

  • grid bias — Electronics. the potential difference applied between a grid and the cathode of a vacuum tube. Also called C bias. [1925 30] * * * …   Universalium

  • grid bias — /ˈgrɪd baɪəs/ (say grid buyuhs) noun a fixed voltage applied between the cathode and the grid of a radio valve …   Australian English dictionary

  • grid bias — noun Electronics a fixed voltage applied between the cathode and the control grid of a thermionic valve which determines its operating conditions …   English new terms dictionary

  • grid bias — noun : a small constant component of the grid potential in a vacuum tube that is usually negative for ordinary triode control grids …   Useful english dictionary

  • grid bias voltage — tinklelio priešįtampis statusas T sritis fizika atitikmenys: angl. grid bias; grid bias voltage vok. Gittervorspannung, f rus. напряжение сеточного смещения, f pranc. polarisation de grille, f …   Fizikos terminų žodynas

  • grid-bias battery — tinklelio baterija statusas T sritis fizika atitikmenys: angl. grid bias battery vok. Gitterbatterie, f rus. батарея сетки, f; сеточная батарея, f pranc. batterie de grille, f …   Fizikos terminų žodynas

  • Bias (disambiguation) — Bias is an inclination towards something, or a predisposition, partiality, prejudice, preference, or predilection. Bias may also refer to:In science and statistics: * Bias (statistics), the systematic distortion of a statistic ** A biased sample… …   Wikipedia

  • grid leak — noun : a resistor used in parallel with a capacitor in the grid circuit of a vacuum tube to limit grid bias by drawing off excess electrons that accumulate on the tube grid * * * Electronics. a high resistance device that permits excessive… …   Useful english dictionary


Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.