Upgrading PS01 to PS03 with older N72's

[casino66]

Hi Tim

I bought 2 assembled N72's from you back in early 2003
and want to add either some A12's or A12b's.
I understand I will need to replace the PS01 with a PS03
for the A12's to work.

Concerning the N72's, I read you mention in another thread
"If they don't have on-board regulators, you'll have to add a 2W 75 ohm resistor to make them work with the PS03"
I'm assuming my N72's being older don't have the on board regulator.
Can you please tell me where this resistor needs to be added
or direct me how to find out?
Also, let me know if there are any other concerns when changing from PS01 to PS03 with older N72's.
I still have the original schematics and bill of materials.

Thank you

[tpryan]

If you have the schematics, you don't have to assume anything about the local regulator. Is it there or not?

[casino66]

Good point, no there isn't a voltage regulator.

I finally found your suggestion of using a zener diode
to drop the voltage @ 6v and how to install it.
Is this preferable to adding a 2W 75 ohm resistor
as you also have suggested?
Do you mind explaining how the resistor is implemented
so I can understand which makes the most sense?