How do I get Sidebars to appaer on Posts page?

I'm new to this and I may be missing something basic; I've tried searching on it but found nothing.

How can I get the sidebars to show on the Posts page?

As it is, it doesn't matter whether I set 'Front page displays' to Posts or a static page with a designated posts page, the sidebars disappear. They are working fine everywhere else and if I change the designated Posts page to something else, then they reappear on the page I first had designated.