NC-125

Great news to hundreds who want maximum selectivity at minimum cost ! The only receiver with the famed select-o-ject built in !

NOW AVAILABLE FOR IMMEDIATE DELIVERY

Now at last, you can get immediate delivery on the receiver that gives you more selectivity per dollar - the only receiver with the famed Select-O-Ject circuit built in ! And that's only one of the many fine features that make the NC-125 tops in receiver value ! Covers 550 kcs. - 36 mcs. in 4 bands. Voice, CW, NFM (with adapter). Edge lighted, direct-reading scale. Amateur, police, foreign, ship frequencies clearly marked. National Select-O-Ject built-in (rejects any selected audio frequency 45 db - boosts 38 db). Three microvolt sensitivity (for 10 db signal/noise ratio on 10-meter band). S-meter. AVC, ANL, ant. trimmer. Variable CW pitch control. Separate R.F. and audio gain controls. Volt. reg., stabilized oscillator. Jack for phono or NFM Adapter. Audio essentially flat to 10,000 c.p.s.

FEATURES

  • Continuous Frequency Coverage of from 560 kilocycles to 35 megacycles.

  • Direct frequency Reading Slide-Rule Dial

  • Calibrated Bandspread Tuning for 10-11, 15, 20, 40 and 80 meter Amateur Bands

  • Automatic Noise Limiter

  • Built-In Select-O-Ject

  • Accessory Connector Socket

  • Stabilized Voltage Regulated Circuits

  • R.F. Amplifier Stage with Panel Trimmer

  • Two I.F. Amplifier Stages

  • Separate Loudspeaker in Matching Cabinet

    GENERAL DESCRIPTION

    The NC-125 is a superheterodyne Radio Receiver having a complement of eleven tubes, including a rectifer and a voltage regulator tube, with a continuous frequency coverage of from 560 kilocycles to 35 megacycles. This Receiver is designed for the reception of amplitude modulated voice or music and code telegraph signals throughout its entire frequency range. A calibrated illuminated slide-rule dial provides direct reading scales in megacycles for each of the General Coverage ranges as will as additional calibrated bandspread scales for the 10,11, 15, 20, 40 and 80 meter amateur bands. The selectivity characteristic is adjustable over a wide range from broad-band broadcast requirements to sharp amateur C.W. reception. This is accomplished by incorporating the well known Select-O-Ject variable audio frequency device in the Receiver circuit design. The adjustable selectivity plus high sensitivity assures the operator of optimum reception during adverse operating conditions. The NC-125 employs a voltage regulator tube to minimize frequency drift in the high-frequency and beat-frequency oscillators. This assures a minimum of frequency drift for both phone and code reception. Other highlights include an accessory connector socket, separate loudspeaker in matching cabinet and front-panel mounted S-meter. The separate bandspread control knob and linear logging dial scale makes possible fine, vernier-type tuning for any portion of the frequency spectrum covered by the Receiver. The usefulness of this feature will be outstanding on crowded bands such as the foreign broadcast band etc.

    TUBE COMPLIMENT

    R.F. Amplifier 6SG7
    High-Frequency Osc-Mixer 6SB7-Y
    First I.F. Amplifier 6SG7
    Second I.F. Amplifier 6SG7
    Second Det. - A.V.C. - A.N.L. 6H6
    Phase Shifter 6SL7GT
    Boost-Reject Audio Amplifier 6SL7GT
    First Audio Amplifier - C.W.O. 6SL7GT
    Audio Output 6V6GT
    Voltage Regulator OA2
    Rectifier 5Y3GT

    TUNING SYSTEM

    The three-gang main tuning capacitor, the panel-mounted Trimmer control and four set of coils are used to properly tune the frequency range of the Receiver in four General Coverage tuning bands. The main tuning capacitor and the bandspread capacitor are connected in parallel on all bands. A slide-rule type dial with two separate pointers is utilized. One of these pointers is synchronized with the main tuning control and the other with the bandspread control. The General Coverage portion of the slide-rule dial has four scales accurately calibrated for direct reading in megacycles.

    BAND FREQUENCY COVERAGE
    A 12.0 - 35.0 Mc.
    B 4.4 - 12 Mc.
    C 1.55 - 4.4 Mc.
    D 0.56 - 1.55 Mc.

    It will be noted that Band D encompasses the entire Standard Broadcast Band. The respective scales are marked with heavy white scorings to clearly locate for the operator such short-wave features as the Amateur, Police, Ship Frequencies and Foreign Broadcast bands. The Amateur bands tuneable by the NC-125 are listed below with their band locations. Five accurately calibrated Bandspread scales are provided on the slide-rule dial for each of the specified Amateur bands.

    BAND AMATEUR BAND FREQUENCY
    A 10, 11 27.16 - 29.7 Mc.
    A 15 21.0 - 21.5 Mc.
    A 20 14.0 - 14.4 Mc.
    B 40 7.0 - 7.3 Mc.
    C 80 3.5 - 4.0 Mc.

    AUDIO OUTPUT

    Two audio output circuits are provided as follows:

    (1) The Loudspeaker supplied with the NC-125 is of the permanent magnet field type and is mounted in a cabinet finished to match the Receiver. An output terminal strip is mounted at the rear of the Receiver for convenient connection of the Loudspeaker.

    (2) A Phones jack is mounted on the front panel and is wired so as to silence the loudspeaker when headphones are used. The headphones load impedance is not critical permitting a wide range of headphones types, including crystal, to be used.

    SELECT-O-JECT

    The NC-125 Receiver incorporates a built-in Select-O-Ject audio frequency circuit. By proper adjustment of the front-panel mounted controls associated with this circuit any single frequency selected in the range of approximately 80 to 10,000 cycles may be boosted or rejected. In phone reception the Select-O-Ject may be used for the rejection of interfering heterodynes . In C.W. reception interfering signal may be rejected or, alternatively, the desired signal may be selected and amplified. In the reception or amplification of music, the Select-O-Ject may be used as an adjustable bass boost.

    SIGNAL STRENGTH METER

    Signal input reading are indicated in S-units from 1 to 9 in 5 db. steps and in db. above 5-9 from 0 db. to 40 db. on the panel-mounted signal strength meter. The S-meter employs a 0-1 milliampere movement and is connected in a bridge circuit. A variable resistor is placed in series with the meter to allow adjustment of the pointer to its electrical zero setting. The correct dial setting for any specific station on the dial is that setting which provides maximum deflection of the meter pointer.

    POWER SUPPLY

    The NC-125 Receiver is designed for operation form a 105/130 volt, 50/60 cps., A.C. source of supply. Normal power consumption is approximately 91 watts. The built-in power supply provides all voltages required by the heater and B supply circuits 2.85 amperes at 6.3 volts and 92 milliamperes at 250 volts, respectively.

    PHONO INPUT

    A Phono input jack is mounted on the front panel and can be used to connect auxiliary apparatus, such as a record player pick-up or microphone into the audio system of the receiver. This input circuit is of high impedance providing a suitable match for such external equipment into the first audio amplifier stage.

    ACCESSORY CONNECTOR SOCKET

    A standard octal type socket is mounted at the rear of the Receiver to permit convenient connection of a narrow-band F.M. adaptor. Reception of narrow-band F.M. signals may be accomplished by plugging a National Model NFM-73B directly into the Accessory Socket and inserting the phone plug supplied with the unit into the Phono jack at the front of the Receiver. The drawing of the Accessory Connector Socket on the Schematic Diagram show the various connections made to the pins of the socket and voltages available. As will be noted B+ and filament voltages as well as I.F. output are available at this socket permitting the connection of auxiliary equipment. Consideration must be exercised to prevent loading any of these supplies beyond that for which they are designed.

    NC-125 149.50*
    NC-125TS (matching spkr.) 11.00

    *Slightly higher west of the Rockies.

    Source: Instruction Manual for The National Model NC-125 Radio Receiver, February, 1952 QST

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