[Radio Wrangler]

Hi Miguel,

When the signal passes through zero volts at the speaker and at the input, the valve is biassed just as in its no-signal state, and the anode is passing 40mA.

40mA may make only a little heat, in the resistance of the copper wire of the primary, but more importantly the current creates a magnetic field in the transformer core. The collapse of this field as the valve current falls below 40mA is what powers the positive half of the cycle, when the anode swings far above the HT voltage.

Transformers for single-ended stages like this are more like chokes with an added secondary. Design effort has to go into making enough inductance, and for it to not saturate when the valve is at peak current... approaching 80mA

An ideal transformer would have no resistance from anode to HT, so the average anode voltage must equal the HT, and the anode must swing equal amounts below and above the HT voltage.

Have you heard of 'load lines'?

David