Avo Valve Tester

[pwdrive]

I do know that ac is positive and negative, but they have clearly put + and - on each end of the winding on the diagram.    As is is flipping from one side to the other, I don't see how they can say one end is positive and the other end is negative!
Bob

It might be for illustrative purposes in conjunction with the detailed circuit description.

Are there any markings on the transformer for that winding?

Lawrence.