I have a copy of "The Mersey Railway" by G.W.Parkin. On p.13 under "Proposed Extensions not Implemented" it reads " ....A turnout south of Upton Station was to connect with the Mersey Line at Birkenhead Central. The Wirral Company had no funds to execute these works and it was the M.S. & L. (later to become the Great Central) which finally joined up with the Wirral at Bidston, but not to Birkenhead Central. Standing on the B'head Cen.down platform, a discerning eye can detect how the building line of the original station buildings has been set back to permit the proposed line to sweep round and eventually take up alignment under Borough Road. Certain occupants of this building today need no reminding of this particular piece of railway History
, for they work in triangular offices ! "
Hope the above throws a bit of light on the subject.
re: sub-station at the top of Singleton Ave. Chris recalls the mercury arc rectifiers (Frankenstein models). They must have gone by the mid '50's as I recall gazing into the building and looking at a pair of big rotary coverters. These did the same AC to DC conversion but were slightly more modern technology. I also remember a bit in B'head News
saying the Singleton Ave. area was the last bit of B'head to be changed from DC to AC. At a guess this would be 1958/9 ish.