The following bulletin was produced by National and intended for the National NCX 5 transceiver.

The customer Service bulletin is CSB 66 - 1

An additional modification to the NCX 5 transceiver:
Low AM receive audio level/ SSB audio level normal
Change L22 inductor at diode D11 (am detector) from the single layer unit supplied to a larger inductance.  A small 3 section choke works well.  This will raise the received am audio and prevent the operator from having to reset the volume control when changing receive modes.    

Compliments of WA7LYO