Does anyone have any info or service bulletins? The serial number is 524 1587. It also has wrinkle finish paint along with the XCU-303 xtal calibrator installed.
I dug through my files and found a 1998 email from John Sehring regarding a 1960 Hints and Kinks piece from CQ magazine. The email indicates the "hint" was from the National factory.
Change C55 from 33 to 5 pf.
Change R46 from 120 to 270 ohms.
Interchange resistors R72 and R73 (e.g., make R72 100K and R73 470K).
I have not made these changes to my own 303. It DOES need a better 9.6 Mhz mixer image trap than the useless one (L18,C86) provided by National. Great radio, though!