The first Deltas

[mrfs42]

Was the first use of Delta circuits on LT lines at Stanmore (release for calling-on discs MK43/44) and Lambeth North (delayed clearance for BP13 side of BP12/13 with the crossovers reversed) when the Bakerloo took over the Stanmore branch in '39? Or were they installed earlier?

[Tom]

My guess is this would be one of the earliest installations of the original sort of delta, with a normal DEV track relay (as opposed to the later 10kc/s rail circuit.

[mrfs42]

So when did the 10kc/s circuit come out - it appeared in print c1964 with the IRSE text book "Holding the Route" by Challis?

This book is mainly about LT route holding techniques, but presented using BR type layouts.

[Tom]

I'm not too sure - sometime in the late 50s or early 60s. I'll have a look through the archive of D.O. Notices if I get a quiet moment and try and get a more exact date.

What I do know is that Watford South Junction had one of the older style deltas until a few months ago, and that was post 1954.

[Deleted]

whitechapel still has them

[Tom]

And the dates are:
33 1/3Hz Delta - from July 1938
10kHz Delta - from December 1956.

[JR 15secs]

tom said:

I'm not too sure - sometime in the late 50s or early 60s. I'll have a look through the archive of D.O. Notices if I get a quiet moment and try and get a more exact date.

What I do know is that Watford South Junction had one of the older style deltas until a few months ago, and that was post 1954.

Tom are the DO notices located on the 3rd flr T Hse Holborn or Eagle?