Colin,
The voltage on the 'collector' together with the voltage on the front mesh of the storage tube depend on a +600V supply derived from a separate winding on the HV transformer. So the lack of +150V on the collector traces back to the lack of -1475V on the CRT.
The usual suspects for failure of the -1475V are the heat-sinked drive transistor Q1195 and the power supply decoupling components C1198 and L1198. Q1190 is also worth checking and C1224 (is it one of the failure prone tantalums?) will kill the drive to Q1195 if it (ie C1224) goes short circuit. There is a fuse in the unregulated supply to Q1195, (F814) which is on the low voltage regulator board.
There are of course other potential failures on the HV side of the -1475V supply.
Regards,
Roger
