['LIVEWIRE?']

Possibly one or more transistors is.are faulty. DC coupled amplifiers can be a bit of a pain because a fault in one transistor or other device produces a 'knock-on' effect bu upsetting the voltage readings on others. I'm not familiar with the transistor Black Box, but I'd be inclined to suspect the output transistors, which almost certainly will be a PNP/NPN pair, no doubt with a common heatsink or cooling clip. If the Newmarket Transistors are as prone to the 'tin whisker' problem as Mullard types this could be the cause of the excess current consumption