As with the HRO, an elliptic hub was required to make the PW-D work but inside the NC-100 gear box were several changes.Gone was the large split-gear, replaced with dual driven gears, one of which was spring-loaded for anti-backlash, driving via reduction gearing a large condenser drive gear.With the use of a movable cast aluminum coil box called a "catacomb," all of the coils would be mounted in individual shielded compartments with short contact pins mounted in molded insulators on top of the catacomb.
When shipped, the coil catacomb was screwed to one side where a guide pin was located to prevent any damage due to rough handling.
When the receiver was installed, this screw had to be removed to "unlock" the coil catacomb.
This approach eliminated the spring loaded drive of the HRO gear box and replaced it with a much easier to operate gear box.
Since the NC-100 was intended for the SWL or intermediate-level ham, a different type of signal strength or tuning indicator was utilized.
A single RF amplifier provided pre-selection and good reduction of images up to about 15mc.
A separate Local Oscillator reduced the noise associated with the typical "inexpensive" Converter stage and a separated Mixer stage accounted for the three tuned circuits that were necessary in each coil set.
James Millen, National Co.'s General Manager and Chief Engineer, was one of the designers that insisted the best receiver performance was achieved using plug-in coils.
But, how to effectively eliminate the valid arguments against plug-in coil use in a new product?
The split-contacts were not soldered together but rather had the screen voltage wires connected to each of the two halves of the contact and when the coil pin, which wasn't connected to anything inside the coil catacomb, engaged in the two halves the circuit is completed and the screen voltage was then routed to the RF and IF amplifiers.