Museum of the Broadcast Television Camera

Marconi MkIII Television Camera turret removal details

Marconi MkIII Television Camera turret removal details

The complete turret assembly can be removed to allow the Image Orthicon tube to be changed. The black "focus flattening coil" located in the front of the scanning yoke is removed to allow the I.O. to be withdrawn forwards.


In the left picture the disk of the variable density filter (wedge) can be seen with the transparent and dark ends abutting. It had a 2 stop range. Above is the gearbox that translates one rotation of the lens change control crank into a quarter turn of the turret. This movement is so designed as to start slowly, speed up, and then slow down as it approaches the next position.


Removing the turret plate and turret Assembly, first the large black knob in the dead centre of the turret, releases the turret plate with the 4 lens positions and lens fixing clamps. This is all that needs to be undone to remove the turret plate, It may be stuck in due to corrosion of the alloy. If you remove this it will expose the filter wheel and behind it the rotating variable density filter. Be extra careful with this as it breaks easily and is utterly un-replaceable. It is not necessary to remove the the turret plate to remove the complete turret assembly.
Make sure that the turret plate is either secure or removed. Undo the 4 large chrome bolts in each corner and it should just pull forward. The rubber gasket is fixed to the camera body so you may have to run a sharp thin knife around between the rubber and the turret assembly. There is a 18 pin Painton connector that should just separate, I have never known that to stick and there is a mechanical linkage that should just separate (turret drive). Lever carefully if you have to and try jiggling it up and down.

Good luck and be careful with the ND filter.