Early '40's Admiral RC50 record changer question

[radiotvnut]

Here's the 78 rpm record changer out of a '41-'42 Admiral-built Truetone radio/phonograph that I'm about to restore and I'm currently trying to locate service information for this record changer.

The original cartridge is dead; but, this tonearm has a counterbalance spring; so, I may be able to get away with using a more modern ceramic cartridge. At present, I'm leaning towards an 89T powerpoint or an Astatic P51-3. Since this unit uses the driver and output tube of the radio chassis, I should be OK with a 1 volt cartridge.

Now, comes my main question - what is that spring sticking out of the top of the spindle for? It looks like the spring fits in a slot on the spindle; but, I can't get it to stay down.