Sir Mark . . . .

'Cuz that is the middle of the road..

Specifically, I just don't remember (EXCEPTING car radios) where the norm was for there to be other than a push pull output stage with its pair of output transistors and their corresponding bases being fed with a center tapped driver transformer .

The produced audio coming in from that driver transformer secondary can then have its positive swinging nodes controlling the degree of conductance of one of the output transistors while the negative going nodes are then controlling the degree of conductance of the other output transistor.

If the bias level is proper, that amplification could be possible right up to the point where the drive level is making the tips of the sines ever so slightly flat top out at the supply voltage level limitation.

They will then eventually be flat topping even more at higher drive levels and clipping and badly distorting and starting to look and sound like a square wave.

If the bias was in the middle of the road, that initial onsetting of clipping would be symmetrical to BOTH polarity nodes of each corresponding output transistor. However, if the bias error was other than that, the onset of initial clipping on one unit would be starting on one polarity of node before it starts on the other, and at a much lower drive level.





Output transformers from tube vintage sets were using impedances in the 2000-25000 ohms of inductive values to optimally match to plate circuitry of different tubes. 2500 ohms for something in the order of a 50L6 or the other extreme of 25,000 ohms for a battery powered radios output tube. With a like variance of 67-90 volts on the battery set or upwards into the multi hundreds of volts on conventional AF output tubes.

The transistor set is using but a mere fraction of that voltage supply level and with it being a current gain type of device would be using in the hundreds, upwards to a couple of thousand ohms of impedance value for its output transformer.