Prototype National NC-303 Receiver?
NC-303 in an NC-300 Chassis

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• Please send comments, corrections, and additional photos to nick@virhistory.com

Don K1JQ sent me info on his recently acquired NC-303 for my NC-300 & NC-303 serial number database.
I was confused because it was an NC-300 serial number (481-1927) but looked like an NC-303.
This is a REALLY INTERESTING receiver!

It is hard to believe that it is just some ham's conversion - there are too many changes and that just doesn't make sense.
So perhaps it is an NC-303 engineering prototype that was built on an NC-300 chassis?

Some things I have noticed -

• 481-1927 is the last NC-300 chassis number known, so it makes sense it could be used for engineering rather than production.
• The front panel is NC-300 (note cutout above CAL knob), but without NC-300 markings and with NC-303 markings.
• The bezel and knobs are NC-303, obviously
• The NC-303's vernier drive was not added (the hole also appears in late NC-300 front panels)
• The cabinet is NC-300, not NC-303.
• Don acquired the receiver from someone not far from Malden, Mass.
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• The NC-303's Q-multiplier with 12AX7 (V15) has been installed (as in the NC-303 production).
• The NC-303's additional 1st mixer transformer (T3) has been installed (as in the NC-303 production).
• To make room for T3, the S-meter adjust pot has been relocated (as in the NC-303 production)
• To make room for the S-meter pot, the 4H4 socket has been relocated (as in the NC-303 production)
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• The 6AL5 (V14) socket has been added (as in the NC-303 production).
   - And what ham would use rivets rather than nuts/bolts? Hard to use rivets unless you started with a bare chassis?
• To make room for the XCU-303 WWV calibrator, the calibrator socket has been relocated toward the 6AQ5 (as in the NC-303 production).
• To make room for the calibrator socket and 6AL5 socket, the audio transformer has been relocated to mount on the rear (as in the NC-303 production),
• To make room for the audio transformer, the speaker terminals have been relocated to the NC-300 AC line cord location (as in the NC-303 production).
• To make room for the speaker terminals, the AC line cord has been relocated to the NC-300 fuseholder location (as in the NC-303 production)
• To make room for the line cord, the fuseholder has been relocated to near the 4H4 (as in the NC-303 production)
•  
• The co-ax antenna connector has been added
• To make room for the co-ax connector, the antenna terminal strip has been relocated upwards
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• Summary - the Q-multiplier, T3, co-ax connector, and 6AL5 V14 were added.
  The calibrator socket, audio transformer, speaker terminals, antenna terminals, AC line cord, fuseholder, 4H4 socket, and S-meter pot were all relocated to the same locations as in production NC-303 units.
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• Boy, that was a lot of work!

NC-300 (late model with hole for vernier drive)	NC-303	Mystery NC-300/303	--
NC-300	NC-303	Mystery NC-300/303	Mystery NC-300/303
NC-300 ( I need a better photo)	NC-303 (from WD4EUI)	Mystery NC-300/303	Mystery NC-300/303
NC-300	NC-303	Mystery NC-300/303	--