Note
QST, Aug 1960, inside back cover.
Allied Radio catalog 1962 (copyright 1961), p. 277.
QST, Dec 1963, inside back cover.
QST, Jan 1964, inside back cover.
Allied Radio catalog 1961 (copyright 1960), p. 389.
Allied Radio catalog 1963 (copyright 1962), p. 284.
The NC-270 came in a "Cosmic Blue" cabinet and used National’s Ferrite Filter for selectivity. The ham-band-only receiver covered 80–6 meters. It was double-conversion and used 10 tubes. The optional NTS-3 speaker was $19.95. The receiver and speaker have National's patented Flip Foot tilting devices.
The NC-270 features a patented Ferrite Filter operating at the 230 kHz second IF stage. This filter provides selectable bandwidths tailored for different operating modes:
– 5.0 kHz and 3.0 kHz: Broad and medium for AM.
– 2.5 kHz USB and LSB: Symmetrically shifted passbands that allow instant selection of upper or lower sideband without retuning the main dial or BFO.
– 600 Hz: optimized for CW.
Bifilar "T" Notch Filter: A tunable notch rejection circuit that can be swept across the IF passband, offering greater than 50 dB of attenuation to slice out annoying heterodynes or interfering adjacent carriers.
Automatic Noise Limiter (ANL): An automatic, self-adjusting limiter designed to clip transient noise spikes during AM reception.
Oscillator Temperature Compensation: To counteract drift, the high-frequency first converter oscillator utilizes a zero-temperature-coefficient ceramic capacitor combined with a negative-coefficient compensating capacitor.
100 kHz Crystal Calibrator: A built-in calibrator provides accurate markers every 100 kHz. In tandem with the front-panel Cal-Set control (which mechanically shifts the dial scale horizontally), operators can achieve precise dial indexing.
Specifications
– Intermediate Frequencies (IF):
First IF: 2215 kHz
Second IF: 230 kHz
– Sensitivity: Better than 1.5 uV for 1 watt output (10 dB signal-to-noise ratio).
– Antenna Input: 72Ω unbalanced, with dual connection options (a small coaxial jack and a standard two-terminal A/G strip).
– Audio Output: 3 watts maximum output power (designed for a 3.2Ω speaker, with an automatic speaker-muting phone jack on the front panel).
Tube Lineup
The NC-270 utilizes a robust 10-tube complement plus a voltage regulator and rectifier:
– 6BZ6 RF Amplifier
– 6BE6 1st Converter / Mixer
– 6BE6 2nd Converter / Mixer
– 6BA6 1st IF Amplifier (230 kHz)
– 6BA6 2nd IF Amplifier / Product Detector
– 6T8 AM Detector / Audio Preamplifier / Noise Limiter
– 12AU7 Beat Frequency Oscillator (BFO) / $100\text{ kc}$ Crystal Calibrator
– 6CW5 Audio Power Output
– 0B2 Cold-cathode Voltage Regulator (for HF and BFO oscillators)
– 5Y3GT Full-wave Vacuum Rectifier
References
Brief description. Electronics World, Nov 1960, p. 140.
Brief description. Popular Electronics, Nov 1960, p. 36.
More info: QST, Dec 1960, p. 221.
Review: CQ, May 1961, p. 58.
