add MOH to a 400D line card

add MOH to a 400D line card
(from Tek-Tips.com) I used to modify 400D cards for MOH by replacing the hold resistor with an 8ohm-600ohm audio transformer. The 600 ohm side replaced the resistor (which was wire-wound), and looked good to the phone company as a hold load. The 8-ohm side plugged into a radio's earphone jack. (I put small audio jacks on the plastic handle of the KSU card to keep things neat. Cost: under $5 for the modification.

This seemed like really cool stuff back in the day....