Transformer with strange output- 240V- 5.5mA

Hi all,

I have an unmarked transformer that I got for $5 from a surplus electronics store.

It has four leads- 1 red, 1 black, and 2 white.

I wired the 2 white live and neutral using the red and black as outputs.
The GFI tripped

Red live, Black neutral -white outputs- tested white to white- 0V white to earth/ ground 240V per white lead. White to Earth/ ground 5.5 mA- 4.8mA going through a 22k resistor. A bridge brings it down to 168v - 30v depending on the bridge with 2.4mA. output.

White to live, black to neutral- red and white outputs. tested white to red- 240V white to earth- 0V Red to earth- 240V 5.5mA

I talked to an electrician that agreed that it seemed odd.
Do I have a choke instead of a transformer? Maybe an audio output transformer?

Any answers or suggestions would be appreciated.
I'm making a tube preamp, but I don't think 2.4 mA will run much.

Thanks