You want to double-check that C5 connects from pin 4 (control grid) to the jct. with C6 (which also connects to lug# 4 of the coil and pin 3 of the tube.
C5 provides the feedback to sustain oscillation so it has to be in place. Also double check that the 47K resistor R1 goes from pin 4 to ground.
Maybe post the schematic of the most recent iteration when you get it done.
