Radio Shack Chronomatic-300 User Manual page 16

NOTE: The HEADPHONE jack is stereo but the clock/radio's sound is
monaural.
or pillow speaker, connect an adapter that accepts a 1/8-inch plug
(such as Cat. No. 274-374) into the HEADPHONE jack.
earphone into the adapter. Without an adapter the monaural device
will not work.
earphones, pillow speaker, and a wide selection of high-quality
stereo headphones.
(CS 11/21/95)
LN-03/04
If you want to use a monaural device, such as an earphone
Your local Radio Shack store sells the adapter,
Then plug the