Marconi MkIII Television Camera CCU front panel drawing
Showing the control names and some component locations. R26, R112, R113, & R66 were under a small aluminium flap to protect them from inadvertent adjustment, this delicate flap is often missing from surviving camera channels.
Interesting to note, the up-down light control switch ( frequent use) is next to the channel on-off switch (rarely used)!
Note, the Iris meter, M1, has radium markings on the scale.