Rather than show a sequence of me cutting and gluing the wood together for the cabinet construction - I don't have workshop tools so it's all a bit laborious with hand tools - I decided to explore the function of the internal trim pot, using my mini signal generator and even smaller oscilloscope!
The eagle eyed might see that I've also changed the Cathode resistor once more, now a 270 (measuring 269.4) ohm one and this gives 87.6 & 86.7% dissipation for the valves.
The signal/function generator & oscilloscope combination (+ an additional probe) cost me about £90 including shipping from China. I don't have bench space for nice large units so these are fine for my occasional use - though I might invest in a better scope at some point!
paul-williams7456.weebly.com/