There are generally three kinds of connection methods for beam tetrode tube of tube amplifier, standard, ultra- linear, and triode connection. Its output power and distortion decrease in turn.
Generally, when we use the power tube, the grid voltage is fixed, which is called standard connection. When the grid is directly connected to the screen, i.e. the beam tetrode is connected to a three-stage tube that called triode connection. The ultra-linear connection is between standard and triode connections. which is to connect the curtain grid to the tap of a certain number of turns of output transformer, consider to increase the output power of the standard connection and the low distortion of the triode one.
Ultra-linearity is a kind of negative feedback, whose principle is to obtain the feedback voltage through the output transformer tap to add to the output tube curtain grid. As the grid voltage changes, the output curve cluster of the tube will change, so the grid voltage can be negative feedback by output voltage changes.
Here is a wire connection diagram for IWISTAO 100w pull-push output transformer below, only for you information.