The Doctor's first TARDIS was a Type 50 TARDIS prior to his life as a renegade Time Lord. The First Doctor decided to steal another TARDIS, a Type 40 when he finally departed Gallifrey with his granddaughter Susan Foreman. The Type 50 TARDIS escaped Gallifrey on its own. (AUDIO: Prisoners of Fate)
The Doctor considered taking a broken Type 50 before Clara Oswald persuaded him to go with the Type 40. (TV: The Name of the Doctor)