alternator puzzzle

[Zebra]

Hi, back on this page, not too clever on this!
Just fitted new alternator on my girls K11, after the AA condemned the old one. After 3 days of driving the battery light is on again, but will go out with high revs. Checked and cleaned the chassis earth mounting, tightened the spade terminals on the alternator, but still the same.
Anyone with a an answer, please.
Zebra

 

[davyboy]

Slack belt ?

 

[bls]

A buddy had same problem years ago, the electrical bushes in the starter were badly worn which affects the charging circuit
Not expensive to change..