When the Doctor, Romana and Duggan are locked in the cellar, and Duggan lights the oil lamp, the light from it is too bright and too white to be from any kind of flame-based lamp (which should be a much softer, yellowish "tungsten" kind of light). Instead, the illumination is obviously from an electrical studio light that is off camera.
When Duggan breaks through the stone wall in the cellar, the entire wall (and the adjoining wall to his right side) wobbles revealing it to be a lightweight set and not real stone.
The Count instructs his henchman to lock the Doctor, Romana and Duggan in the cellar. Considering he was conducting top secret time travel experiments in there with some very expensive equipment, surely another room would have been more appropriate. Of course, this was done purely so the scriptwriters could easily enable the Doctor to see the equipment for himself and therefore "deduce" what the Count was up to.