Designed particularly for the discriminating radio amateur, the brilliant new National NC-183 is also ideal for the short wave listener who appreciates topnotch performance and skillful engineering. Sixteen tubes (including rectifier and voltage regulator) are employed in a modern high-gain superheterodyne circuit. The main tuning and bandspread dials are calibrated directly in frequency and both have auxiliary logging scales. Two stages of signal frequency amplification provide that extra measure of sensitivity and image rejection so often needed when receiving conditions are unfavorable and a panel controlled trimmer allows the operator to compensate for variations in antenna loading at any frequency. The push-pull audio stage delivers 8 watts of undistorted audio power to an efficient ten-inch PM speaker. The wide range crystal filter with phasing control, adjustable-threshold automatic noise limiter, tone control and C.W. oscillator pitch control afford exceptional flexibility of performance characteristics, enabling the operator to cope with a wide variety of receiving conditions. Other features include: h.f. oscillator temperature-compensated on all bands; phonograph pick-up jack; accessory connector socket; illuminated signal strength meter with adjustable sensitivity; self-contained output transformer with 500 ohm and 8 ohm terminals operated from 115 or 230 volts 50/60 cycles or, in emergency from batteries or vibrator power supply ; narrow band FM adaptor available (plugs into accessory socket inside the cabinet). Frequency coverage: 540 kc. to 31 Mc. and 48 to 56 Mc.
FEATURES
| 1st r.f. Amplifier | 6SG7 |
| 2nd r.f. Amplifier | 6SG7 |
| 1st i.f. Amplifier | 6SG7 |
| 2nd i.f. Amplifier | 6SG7 |
| 1st Detector | 6SA7 |
| h.f. Oscillator | 6J5 |
| Phase Inverter | 6J5 |
| 2nd Detector-A.V.C. | 6H6 |
| Noise Limiter | 6H6 |
| A.V.C. Amplifier | 6AC7 |
| B.F.O. | 6SJ7 |
| 1st Audio | 6SJ7 |
| Audio Output | 6V6GT/G |
| Voltage Regulator | OD3/VR-150 |
| Rectifier | 5U4G |
TUNING SYSTEM
The main tuning and bandspread capacitors are connected in parallel on all bands. This permits bandspread tuning at any frequency within the tuning range. Two r.f. stages are used on all bands and the trimmer for the 1st r.f. stage is controlled from the front panel. Dial calibration is as follows:
| Band | General Coverage | Bandspread |
|---|---|---|
| A | 48 - 56 Mc. | |
| B | 12 - 31 Mc. | 14.0 - 14.4 Mc. 27 - 30 Mc. |
| C | 4.3 - 12 Mc. | 7.0 - 7.3 Mc. |
| D | 1.6 - 4.3 Mc | 3.5 - 4.0 Mc. |
| E | 0.54 - 1.6 Mc. |
CRYSTAL FILTER
A new highly flexible crystal filter provides an adjustable selectivity characteristic with a wide range from broad-band broadcast requirements to sharp single-signal code reception. A phasing control permits attenuation of interfering signals.
NOISE LIMITER
A new concept in noise limiter design is included in the NC-183 Receiver. This new limiter could be termed "double action plus" and the noise limiting action is equally effective on either phone or code reception. A panel-mounted threshold control permits adjustment of the level at which limiting action starts.
NARROW BAND FM ADAPTER
The NFM-83 Adaptor makes the NC-183 an excellent receiver for narrow band FM. A 6H6 tube is employed as a noise suppressing ratio-type discriminator and a 6SK7 i.f. coupling stage eliminates undesirable loading of receiver circuits. Instant selection of AM or NFM by phono-radio switch.
CONTROLS
Main tuning; bandspread tuning; band switch; RF gain - AC on/off; AF gain; send/receive switch; AVC/MVC switch; tone; CWO switch; CWO pitch; limiter; selectivity; phasing; RF trimmer; radio/phono switch.
SELECTIVITY
The selectivity switch of the wide range crystal filter permits a choice of six progressively narrower i.f., pass-bands. Maximum and minimum selectivity characteristics are as follows:
| 6 db. down | 20 db. down | |
|---|---|---|
| Selectivity Switch "OFF" | 3.9 kc. | 8. kc. |
| Selectivity Switch "5" | 80 cycles | 400 cycles |
SENSITIVITY
Measured with a standard 300 ohm dummy antenna, sensitivity of the NC-183 is better than 1.5 microvolts for a 6 db. signal/noise ratio throughout the entire frequency range.
IMAGE REJECTION
Signal/image better than 40 db. at 30 megacycles.
POWER INPUT
Approximately 125 watts at 115 v., 50/60 cycles. 1 phase a.c. (easily adaptable to 230 v. service as well as emergency operation from batteries)
AUDIO SYSTEM
Undistorted Power Output - 8 watts.
| Tone Control at 10 | 60 to 12,000 C.P.S. |
| Tone Control at 0 | 60 to 1,000 C.P.S. |
| Speaker Socket | 8 or 500 Ohms |
| Phone Jack | Not Critical |
A high impedance phono input jack is provided at the rear of the receiver and the phono-radio switch and phone jack are on the front panel.
PHYSICAL DATA
Table Model, 19 3/4" x 10 1/8" x 15", 56 lbs., Gray Enamel finish. Rack Model, 10 1/2" panel height, 56 lbs., depth behind panel 17 1/2" overall, Black Wrinkle finish.
| NC-183T Table Model (with speaker) | Net $269.00 |
| NC-183R Rack Model (with speaker) | Net $269.00 |
| NFM-83 Narrow Band FM Adaptor | Net $16.95 |
| TB-5 Tilt Base | Net $3.95 |
| NC-183TS (Table) or NC-183RS (Rack) Speakers | Net $14.00 |
Source: National Radio Products 1948 Catalog. Photo from KG7BZ
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