"Barry Streets" wrote in message
news:PwAkd.393209$D%.27527@attbi_s51

The Application is a party line audio intercom that has 20 to 30
stations, phantomed powered over the balanced audio lines. It's the
transformer that drives the balanced line, and the center-tap is used
to extract the dc power. Hope this helps as the system was custom
built 20-30 years ago.

So measure one of the other 19 to 29 transformers that still work.

Measure DC resistance of the windings with an ohm meter.

Measure turns ratio by applying a small audio voltage to one winding and
measuring the voltage across the other winding(s).

If you want to be fancy, you can use a scope and a higher-powered signal
source to find out what levels it takes to saturate the cores.