BC-1A AM Tuner
Features
This exciting tuner incorporates features not usually expected in an AM circuit. Designed especially for use with high fidelity systems, the BC-1A provides broad bandwidth, and is capable of flat response from 20 cps up to 2 kc with 7 db of pre-emphasis at 9.5 kc to compensate for station rolloff above 5 kc. This pre-emphasis is employed to provide additional "brilliance" to the higher frequency sounds. Frequency coverage is from 550 to 1600 kc. RF bandwidth is 20 kc. Additional outstanding features are a 10 kc whistle filter to reduce the whistle caused by beats between the carrier tuned and an adjacent channel. 6 db signal-to-noise ratio at 2.5 uv. Pre-aligned RF and IF coils, for simplified alignment. Only three minor trimmer adjustments to make.
Most commercial AM tuners conform to a definite circuit configuration and engineering has been toward high sensitivity and selectivity but with standard bandwidth, which is rather narrow, limiting response from the tuner to 5 kc. or less. In many cases, this is sufficient, since many broadcast stations limit their transmitter response to 5 kc. A large number of stations have flat response to 10 kc, however, and it is impossible for one of the standard tuners to take advantage of the wider range transmission. In rare cases, full bandwidth AM to 15 kc. will be found and the program material in this case can almost be considered "hi-fi" except for the necessarily limited dynamic range. Obviously, almost all of this type of signal would be lost in a conventional tuner and the station would sound the same as one with 5 kc limited response.
The efficient, modern circuit uses miniature tubes throughout plus two crystal diodes connected in a voltage doubler circuit, which has several advantages. Audio and AVC voltage output is double that obtained with conventional types, so less audio gain is required and AVC action is substantially improved, reducing distortion and improving performance on modulation peaks. The power supply is built-in with well-filtered B+. Incorporates AVC (automatic volume control)--two outputs, one fixed and one variable--two antenna inputs, one for low impedance, low-noise external (furnished with kit), and one for high impedance long wire.
A wide band AM tuner also is easier to tune than a conventional tuner, the response and noise quieting remain the same over a wide tuning range. This is a great help when the "uninitiated" members of the household use the system.
Specifications—Tuning Range: 550-1600 kc. IF Frequency: 455 kc. Antennas: Low impedance electrostatically shielded loop or conventional straight wire. Outputs: Two outputs are provided, one at medium impedance fixed level, the other at low impedance from a cathode follower with variable level control. Output Voltage: 1 volt rms with 3 microvolt input up to 11 volts maximum with .1 volt input. 400 Cycle Distortion (measured with 100 µvolts signal): at 70% modulation measured as 2.6% with 1.6% measured from the generator. Hum and Noise: 40 db below 100 uvolts 30% modulated at 400 cps. Sensitivity for 1 volt output: better than 3 uvolts across entire band measured from source impedances of 50 ohms or less. Signal to Noise Ratio: Better than 12 db across entire band at rated sensitivity. Adjacent Channel Selectivity: 27 db with broad response, 29 db narrow band response. Tube Complement: 1-6X4 rectifier, 1-6BA6 RF amplifier, 1-6BE6 oscillator-mixer, 1-6BA6 IF amplifier, 1-12AU7 audio amplifier-whistle filer-cathode follower output, 2 germanium diodes voltage-doubler detector. Power requirements: 105-125 volts, 50-60 cycles, AC 26 watts. Dimensions Overall: 12 9/16" long x 3 5/8" high x 5 3/8" deep. Shipping Weight: 8 lbs.
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