The transistor driving the transformer will always be turned "on". Just how turned "on" the transistor is depends on where in the sine cycle we are. The transistor will never be turned "off" or
switched off in class A. The current in the transformer reverses polarity during the cycle when the magnetic flux in the transformer core collapses. That is why, with a transformer coupled class A amplifier, the voltage on the collector of the transistor can reach a theoretical value of x2 Vcc. But the key here is that the
collector current NEVER drops to zero in a class A amplifier/osc unless it is being driven into clipping.
Circuit for reference:
View attachment 38400