Suggestions.- 1.- you remove the flyback and the hot, you connect a 680 ohms 20w resistor or a 75w bulb from the b + to ground and you touch how much you have of b +. Under these conditions the source has to be stable. This allows you to be sure about the regulation of the source.- - 2.- Connect your frequency meter at the base of the hot and check the frequency 15750 cycles.- Greetings.