The NC-80X is a ten tube superheterodyne covering frequencies from 540 to 30,000 kilocycles in four ranges. The NC-81X employs the same circuit but is fitted with a special tuning condenser and special coils to provide full band spread on the 10, 20, 40, 80 and 160 meter amateur bands; frequencies between these bands cannot be covered.
|High Frequency Oscillator||6K7|
|Beat Frequency Oscillator||6J7|
The battery models have no rectifier tube and employ a Type 6V6G output tube instead of the 25L6G.
CIRCUIT: The circuit consists of a first detector and oscillator employing separate tubes, three stages of I.F. amplification, a bias type power detector and a resistance coupled beam power output stage; maximum undistorted audio output is 2 1/2 watts. A separate tube is employed to provide amplified and delayed AVC and a separate beat frequency oscillator is coupled to the 2nd detector for c.w. reception.
TUNING SYSTEM: The tuning system is of an entirely new design and employs a multiple-scale dial of the full-vision type, accurately calibrated in megacycles. Several unusual features are incorporated, such as the mirror, for overcoming parallax, the auxiliary linear scale, numbered from 0 to 100, and six adjustable frequency markers by means of which any particular stations or frequencies may be "logged" on the dial itself. A dual vernier reduction drive is used which provides a 55 to 1 reduction over any narrow band of frequencies with automatic shift to an 11 to 1 reduction for conveniently and rapidly moving the pointer to another section of the scale.
CRYSTAL FILTER: Provides continuously variable selectivity over a range of from 300 cycles to 7 kilocycles.
OUTPUT CIRCUIT: The output terminals of the receiver are connected in the plate circuit of the 25L6G power output tube. The speaker terminals are at the rear of the chassis. A headphone jack is mounted at the rear of the chassis and is wired in such a manner that the speaker is quiet when the headphones are in use.
POWER SUPPLY: The power supply is of the 110-120 volt AC-DC type, except in models designed for 220-240 volt operation and certain other special services, such receivers being equipped with a suitable built-in power transformer.
Battery models are designed for 135 volt operation with a 6-volt heater supply. The receiver is fitted with a suitable cable and plug for making the connections. The B-supply drain is approximately 35 milliamperes, while the heater current is 2.8 amperes.
|NC-80X Receiver, complete with tubes, crystal filter, 8" PM speaker chassis, etc. for 115v. AC or DC||List Price, $146.65|
|NC-81X Receiver, Amateur Model, complete with tubes, crystal filer, 8" PM speaker chassis, etc. for 115v. AC or DC||List Price, $146.65|
|Type DSC-8G Metal Cabinet for 8" speaker, same finish as receiver||List Price $8.00|
Note: Either of the above receivers can be supplied modified for Battery Operation 6v. heater, 135v. B-supply.
Source: The National NC-80X, NC-81X instruction manual, 1937 QST's
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