Hello Falconquest. Tubes work by making electrons flow from the cathode to the "Plate" (or anode). "Plate voltage" refers to the amount of attraction (positive voltage) we apply to the plate to get the electrons to flow. The higher the voltage, the more eager the electrons are to flow. We control the amount of "normal" flow by establishing the "bias" (the no Music) flow by appropriate circuitry. By applying a signal (the music) to a fine screen (like the one that keeps the flies from coming in your window - the grid)) in between the cathode (a cylinder of metal coated with a substance the produces a cloud of electrons when heated) and the plate. Physical construction of the tube's innards vary, but you get the idea. The normal current flow is changed by the signal on the grid. It's that change that interests us. That changing electron flow goes through a transformer. The transformer has two sets of wires wrapped around it's metallic core. The Primary Winding carries the current going through the tube on its way to the source of positive voltage. The current varies with the music and produces a voltage in the Seconday Winding of the transformer. The transformer's secondary is connected to your speakers and produces the sound in your room. There are ways of eliminating the output transformer, but it's quite a trick. The easiest (and cheapest) way to get more power out of the amp is to raise the Plate Voltage. But that shortens the life of the tube. So, since it's the change in the current flow through the tube that produces the musical output, if we can get the same amount of current change at a lower plate voltage, we get less wasted heat, lower power consumption, less expensive output transformers, and longer tube life. Bob Carver produces certain models of amps with tubes that run so cool that you can put your hand on the tubes while the music plays and not burn your hand. Those tubes last for decades, not years. Happy listening.
