I think the first Dr Who to use video for the outdoor sequences was Robot in about 1975. Can't remember what cameras they used.
Yes, quite right: '
Robot breaks entirely new ground by being the first [Dr Who] story shot entirely on shiny-but-cheap-looking video, as by 1974 video cameras had become lightweight enough to allow the programme-makers to film all the exterior sequences on VT. Theoretically, this means that for the first time CSO effects can be used to make a monster look gigantic when it's
outside, without the effect looking silly.' - Lawrence Miles and Tat Wood,
About Time. It's interesting how often Dr Who crops up on this forum, and equally interesting how often the Beatles crop up in Miles and Wood's Dr Who books.