bias
Like many electronic devices, tubes (aka valves) are closer to linear in certain operating ranges--meaning the output is a scaled version of the input when operating in the linear region. However, these linear regions are not typically at zero volts. So a DC bias is added to the AC input signal, shifting the signal into the linear region of the device. The DC bias can be removed from the output, leaving the amplified signal. Essentially the bias shifts the "zero" point for the signal to match the amplifier characteristics. Choosing bias is an important consideration in amplifier design. Amplifiers are designated by a "class" according to their bias--class A, class B, class AB, class C (there are other classes but they aren't used with tubes). Because the bias signal is the zero signal input, the bias determines how much power the tube uses when idle. For example, a class A amplifier is biased to the middle of the tube operating range so it uses about 50% power when idle, which is wasteful and makes a lot of heat.
forward bias is in the direction a junction or vacuum tube wants to conduct currentreverse bias is in the direction a junction or vacuum tube opposes conducting current
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low input impedance
In a two stage RC coupled amlifier the rransistor are identical and a common power supply is used. the output is provided to the first stage of the amplifier wher it is amplified and this output is uses as a input for the sexound stage this is amplified once again by the other transistor in the sexound stage and the final out put is obtain.
Base resistor method (or) Fixed bias methodBiasing with feedback resistor (or) Collector to base bias methodVoltage divider bias (or) Self bias
You cannot build a power tube amplifier without bias. At minimum, you need some kind of negative bias on the control grid, and you might need positive bias on the screen grid as well as cathode voltage on the suppressor grid.
To bias the transistors at 0.7 Volts.
That would be a TWT amplifier (traveling wave tube).
You can use a radial tube in a bias ply tire BUT you can not use a bias tube in a radial tire. The sidewall flex of a radial tire is greater than that of a bias ply. A bias tube cannot flex as rapidly as a radial tube and so the resulting friction or rubbing create too much heat and the tire/tube combination will blow.
Symptoms of a bad phase inverter tube in a tube amplifier may include distorted or weak sound output, loss of volume, excessive noise or hum, and unbalanced tone.