Vyga 3

You may be looking for Vega 3.

Vyga 3 was a planet on which an Earth colony had settled around 2350. Labs were built in the wasteland outside the city. An ineffective legal and policing system resulted in the development of an eccentric native culture run by criminals. The Fourth Doctor visited Vyga 3, having apparently located one of the segments of the Key to Time there, but it was actually a weapon which emitted a fluctuating chronon wave when activated. (COMIC: The Seventh Segment)

The Seventh Doctor and Melanie Bush once encountered were-tarantulas on Vyga 3. (AUDIO: Maker of Demons)