Does anyone know what this component is?

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phil99

Guru

Joined: 11/02/2018
Location: Australia
Posts: 2626
Posted: 08:23am 22 May 2025      

It will be a SCR. Gate and cathode are marked so the middle pin is the anode.
At a guess the 250 is the voltage rating.

Possible substitutes might be C106D1, C122E, BT151.