Proper way to bias a hot wire barretter

[mazurov]

I recently scored Weinschel M926 barretter (see picture), seemingly in good working order. The LF output shows 150-ish ohms which sounds right. The bias is specified at 4.5 mA on the case.

I don't quite remember how to use this thing. Shall I get a bias tee on LF out? I'm looking at old books and it seems ppl used batteries to bias barretters when they were hot. Also, my supply only steps in 1 mA steps, do I need to worry about 0.5 mA difference?