NC-300 Converters

The NC-300 Converters are of the broad-band, crystal-controlled type. The output (IF) frequency is 30 to 35 megacycles to correspond to the X band frequency of the National type NC-300 receiver. The slide rule dial of the NC-300 incorporates three separate dial scales to provide direct-reading frequency calibration when the converters are used with this receiver. In addition, all operating voltages required by the converters are available at the accessory socket of the NC-300. If desired, the converters may be used with any receiver which will tune the frequency range of 30 to 35 megacycles. In this case, power for the heaters and plates may be provided from any source capable of furnishing 6.3 volts a.c. at 1.2 amperes and 100-150 volts at 25 ma. for each converter.

The following is a list of the converters available and their frequency coverage.

Type Amateur Band Frequency Range
NC-300CL 1-1/4 220 - 225 mc
NC-300C2 2 143.5 - 148.5 mc
NC-300C6 6 50 - 54 mc

ANTENNA: The antenna input impedance is 50-75 ohms unbalanced to match coax-fed systems. For optimum performance an antenna designed for each amateur band should be used. This would preferably be the antenna normally used for transmitting.

CIRCUIT: To provide uniform gain over the entire amateur band and to provide the desired low noise figure, the NC-300C1 and NC-300C2 converters each use two stages of RF amplification. In both units a 6BZ7 dual triode is used in a cascode circuit, followed by a 6AK5 pentode. The triode section of a 6U8 is used as a crystal oscillator and the pentode section serves as an amplifier-multiplier. A second 6AK5 pentode is used as a mixer. In the NC-300C6 a 6CB6 provides a single stage of RF amplification. The triode section of a 6U8 is connected as a crystal oscillator and the pentode section of this tube is used as an amplifier-mixer.

INSTALLATION: The National NC-300 Converter Cabinet is designed to provide a convenient and attractive means of mounting the converters. From one to three converters may be mounted in the cabinet which matches the receiver cabinet and is identical in size and appearance with the NC-300 speaker cabinet. A four-position switch is mounted on the front panel to permit operation of the main receiver or any one of the three converters without changing connections to the receiver or antenna. In addition, and L-C filter is included in the output lead to provide additional protection from interference normally encountered in converter-receiver combinations.

Source: Instructions for the National Converters and Cabinet

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