The Rodgers 500 Series Organs headphone jack is in the same place as the Roland 380.
Plug the headphones in (using a 1/4" plug - or 1/4" plug adapter) for quiet practicing.
Ever have a problem with the organ not playing? Sometimes it's just because someone left the headphones plugged in!
But if you have any organ with dead audio, use a set of headphones to see if it plays through them - this information is very useful to technicians!