The primary sees an approx. square wave of about +/-6V and the primary current is 0.8A (as labelled in the schematic). The input VA is 4.8VA - however this could be wrong since this is a non-sinusoidal wave. However assuming it is correct we can state that the o/p VA will be 4.3VA when we include losses (assuming 90% transformer efficiency). Therefore, if the o/p voltage is 300V, the max. output current can be expected to be about 14.3mA. Practically, expect 12-13mA.
