Chris Denning, 73, admitted 29 charges involving boys aged nine to 16 during an appearance a London court.
But he denied a further 12 charges and was remanded in custody until November 24, when he will face trial on those counts.
The offences he admitted took place between 1967 and 1984.
Denning was one of the original presenters when BBC Radio 1 was launched in 1967 as a direct response to the pirate offshore stations broadcasting pop music.
He was also the first announcer heard on BBC2 when the corporation launched its second television channel in 1964, Britain's third TV station and the first in Europe to broadcast regularly in colour.
Denning was first arrested in June last year by detectives from Operation Yewtree, a police investigation into historic allegations of sex abuse set up after revelations that broadcaster Jimmy Savile was a prolific abuser.
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