The FB-7, designed primarily for the experienced operator, is a seven tube receiver having exceptional sensitivity, selectivity, stability and other characteristics to contend with the crowded C.W and phone bands. Ample sensitivity and selectivity are assured through the use of a circuit employing two stages of high gain I.F. amplification (six tuned circuits). Individual filtering of all circuits, including the oscillators, together with thorough shielding, results in unusual stability. There is no pulling-in or blocking by strong local signals and frequency drift in both high frequency and beat oscillators has been eliminated. Variation of the volume control has no appreciable effect on the pitch of C.W. signals, even at 14. mc.
Fully realizing the tremendous advantages of so-called "single signal" reception of some of the more crowded bands, the FB7 has been designed so as to be readily adaptable to this new type operation. High circuit stability, high I.F. gain special shielding and proper chassis space, make possible the addition of a mechanical filter with its associated "selectivity control" condenser and multi-point switch.
Antenna dimensions are not at all critical, however some experimentation is advised. The antenna circuit consists of a primary coil and a series condenser. This arrangement is used to eliminate antenna tuning effects due to capacity or inductive loading.
|High Frequency Oscillator||224 or 24A|
|Beat Oscillator||224 or 24A|
When using the 180 volt supply, the plate current of the 59 tube is less than 20 m.a. Certain speaker types, however, such as the inductor dynamic, require a filter system, which may consist of a 1 to 1 transformer or a 30 henry choke, and a 1. mfd. condenser. A headphone jack for connecting the phones in the plate circuit of the second detector, is located at the rear left corner. Inserting the phone plug automatically disconnects the grid circuit of the 59 tube, the plate circuit remaining unchanged.
The middle knob is the main tuning control. The left-hand toggle switch opens the main B supply circuit, leaving the heaters lighted. If B battery plate supply is employed, this switch should be thrown to the "off" position at all times when the receiver is not in use. The right-hand toggle switch controls the beat oscillator. The beat oscillator tuning mar be adjusted by means of either of the adjustment screws located at the top of the oscillator coil shield, mounted between the 56 and the 224 tubes. The knurled disc below th tuning knob is the volume control, calibrated in steps of approximately 8 db.
INTERMEDIATE FREQUENCY AMPLIFIER
The i.f. amplifier is tuned to a frequency of approximately 485 k.c. tuning being accomplished by means of the condenser adjusting screws located at the top of the intermediate frequency transformer shields.
FB-7 completely wired including 80 meter coils, less tubes, $55.00
Source: National Radio Products Descriptive Price List No. 210.
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