These are selectors that were originally used in UAX13 equipment

These UAX13 selectors were chosen as they have the ability to use a vertical marking bank to deny access to any chosen level. At Parkend, incoming selectors are only permitted to switch to outlets on level 3 leading to the local final selectors. This prevents users from dialling into Parkend and back out again.
It was found necessary though to change the usual 3000 type 11 ohm HX battery testing relay for something more sensitive as PABX4 finals have a 250 ohm testing battery compared with the usual 150 ohm battery in a UAX13 final. A 62 ohm high speed relay was found to be suitable.

At present the TM relay is not in use.

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Page provided by John Bathgate This page was last updated on 27th July 2008