Elliot, I am not quite sure I understand your question, "Sonically, what are your experiences?" Do I think biasing an output tube makes a difference? That goes without saying; a power tube cannot operate without some chosen parameters: plate voltage, plate and/or cathode resistor values, grid bias, etc, that determine the electronic envelope in which the tube operates. For every tube, there is a data sheet, usually available on-line and/or in published tube manuals. These data show maxima and minima for plate voltage, bias, plate current, etc. The tube has to be set up so its operation falls within these upper and lower limits. And taken with the plate curves I mentioned earlier, you can "see" how different choices within that envelope of values will affect performance when the tube is fed an audio (AC) signal that will have a voltage swing. I use exclusively Atma-sphere OTL power amplifiers, so of course no output transformer, and the power tubes are triodes. In fact, in 45 years, I have never owned a transformer coupled tube amp, only OTLs driving ESL speakers. With Ralph's help, I built my amplifiers so I can set bias current for each of the output tubes separately. This allows me to "match" the tubes for the way they are treated by the circuit. But tubes themselves are unavoidably at least slightly heterogeneous in the way they individually respond to signal voltage.
If you consult with tube gurus, many of them have their own pet theories on where to set bias points for various power tubes, for best SQ and/or for most power, longest life, etc. (Sometimes the settings for best SQ conflict with maximizing tube life.) By the way, the description of vacuum tube operation in my previous post is for triodes only. So called because there are 3 nodes, plate, cathode, and grid. Hence a "tri"-ode, the simplest type of audio tube. Most power output tubes especially on transformer coupled tube amps, will be tetrodes or pentodes. The extra nodes are additional grids that can further control the flow of electrons to the anode, but only the one grid receives the signal (with some very rare exceptions; for example some Berning amplifiers drive the screen grid); normally the one or two screen grids do some of the modulating of electron flow by virtue of the voltage supplied to them. Small signal input tubes and phono and linestage tubes are nearly always triodes.
If you consult with tube gurus, many of them have their own pet theories on where to set bias points for various power tubes, for best SQ and/or for most power, longest life, etc. (Sometimes the settings for best SQ conflict with maximizing tube life.) By the way, the description of vacuum tube operation in my previous post is for triodes only. So called because there are 3 nodes, plate, cathode, and grid. Hence a "tri"-ode, the simplest type of audio tube. Most power output tubes especially on transformer coupled tube amps, will be tetrodes or pentodes. The extra nodes are additional grids that can further control the flow of electrons to the anode, but only the one grid receives the signal (with some very rare exceptions; for example some Berning amplifiers drive the screen grid); normally the one or two screen grids do some of the modulating of electron flow by virtue of the voltage supplied to them. Small signal input tubes and phono and linestage tubes are nearly always triodes.
