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Tubes are usually fixed biased with an external negative power supply ('C battery'); each side normally has independent bias adjustment to compensate for minor tube mismatch. Output impedance Z of a transformerless circlotron where each stage is a single triode with plate impedance of R p and voltage gain of μ is defined by the formula
Class B vacuum tube amplifiers are usually operated with grid current (class B 2). The bias voltage source must have low resistance and be able to supply the grid current. [3] When tubes designed for class B are employed, the bias can be as little as zero. Class C amplifiers are biased negatively at a point well beyond plate current cutoff ...
On June 10, 2014, Kevin Hayes was issued U.S. Patent 8,749,310 for "amplifier bias control". This patent covers the only known technique for observing the true underlying quiescent current (idle current) of an output tube (or transistor) under dynamic signal conditions, and then holding it to the stable target value with a precision of 99% or ...
In electronics, cathode bias (also known as self-bias, or automatic bias) is a technique used with vacuum tubes to make the direct current (dc) cathode voltage positive in relation to the negative side of the plate voltage supply by an amount equal to the magnitude of the desired grid bias voltage.
Plate detector circuit with cathode bias. Cathode bias RC time constant three times period of lowest carrier frequency. C L is typically around 250 pF.. In electronics, a plate detector (anode bend detector, grid bias detector) is a vacuum tube circuit in which an amplifying tube having a control grid is operated in a non-linear region of its grid voltage versus plate current transfer ...
Historically referred to as the "Q" or bias point by engineers, the operating point of a vacuum tube is a condition generally fixed by the amplifier manufacturer. In general, the operating point determines the device's bias value at zero signal input and determines the distribution of harmonics introduced into the output of the amplifier.
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However, the plate dissipation of the 6L6GC, at 30W, exceeds the KT66's 25W, and adjustment of the amplifier's bias is necessary. M-OV ceased glass vacuum tube manufacturing in 1988; their old audio tube types became valuable collectibles.