Thanks. A dim memory came to me today! Reversing field coil connection reverses rotation BUT if the field coil block has no residual magnetism, a perfectly restored dynamo will not produce electricity unless the field coil is energised at start-up of the test run - in the lathe for example. Once running it will self energise and generate electricity. Stop the test, remove battery and restart - there will be enough residual magnetism to self energise the dynamo.
