The CO line cards do not use the 24 VDC for talk battery. The line cards use the 24 VDC for relay operation. That is why you do not have any hum issues on the CO line cards. The ITT Intercom card does have additional filtering to reduce the ripple for the intercom.
If you want to use the supply for just battery, then I would suggest two 1,000 mfd. 50VDC capacitors connected together with a 100 Ohm 2 Watt resistor between the two electrolytic capacitors connected between the AG (+) and AB (-) terminals. Be careful of the polarity. This should wipe out all the ripple and give you a clean AG and AB.
Connect the positive terminal of capacitor 1 to the AG terminal. Connect the 100 ohm resistor to the same terminal. Connect the other end of the resistor to the positive terminal of capacitor 2. Connect both negative terminals of the capacitors to the AB terminal. Connect the load to the positive terminal of capacitor 2 (AG) and AB (-). The "nominal" ripple voltage on a 601 power supply is between .5 and 1 VPP AC. This setup should knock down as much as 10 VPP AC to less than .1 VPP AC. At that point, hum should not be detectable.
Rcaman
