[EdHolland]

Progress today, I figured out the picky perfboard pot placement problem, to get a layout and footprint of components that I like. It also makes sense in relation to the position of the output valves. Also, I chose carefully so that clockwise rotation of the trimmer will decrease the bias voltage, increasing the bias current. That makes most sense to me, turn the dial clockwise to get a bigger reading of the voltage on the cathode resistor.
Here's the board, ready to be cut down and wired in:

   

Wires to the o/p section will attach at the top of the board, for neat routing around the chassis. Feed from the -24V bias supply will attach to the left edge.

Am starting to feel much happier about how this will turn out. 

The board will get a dry run, just to see that the voltages are correct, and adjustable, before tying it in to the circuit proper.

Cheers

Ed