Ekco AC18 HT Unit - using?

[ppppenguin]

Since #2 only has 2 connections it must be a choke. Likely to be connected between the +ve terminals of the pair of 4uF caps. The top image here shows how 2 caps and a choke are normally connected. THis picture shows a valve rectifier rather than your solid state one

http://www.r-type.org/articles/art144a.jpg