C. Crane WR-2A - Manual (Page 27)

GB
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Headphone use
Headphone use with this radio should be fitted with a 3.5 mm jack
plug. Insert the headphones plug into the jack in the front of the
radio. When the headphones are plugged in, the loudspeaker is
automatically disconnected.
IMPORTANT:
Excessive sound pressure from earphones and headphones can
cause hearing loss.
Mute the radio
Press MUTE button on the remote control to mute the radio.
Press MUTE button again or power on/off or volume control to
release the muting.