Tube List: 0A2 (1), 5Y3GT (1), 6AL5 (4), 6AQ5 (1), 6BA6 (8), 6BA7 (2), 6DC6 (1), 12AT7 (3), 12AU7 (1).
* Note: Tube variations depending on vintage.
The Collins 75A-4 is a dual conversion amateur band receiver covering the 160, 80, 40, 20, 15, 11, and 10 meter bands. The dual conversion design utilizes a crystal controlled (fixed) high frequency oscillator and a variable first intermediate frequency (IF). The signal from a type 70E-24 VFO is beat against the variable IF to produce a fixed second intermediate frequency of 455 kc. Selectivity choices include AM, CW or RTTY and SSB reception with mechanical filter selection in the 455 kc IF stage for optimum bandwidths. This is one of the first amateur band receivers to incorporate a selection of the SSB mode of operation. There are provisions for 3 plug-in mechanical filters using 9-pin miniature tube sockets, the 3 kc factory standard and optional filters for AM and CW. The new mechanical filter offers a rectangular selectivity curve with steep skirts for rejection of adjacent frequency interference. This provides optimum selectivity for single sideband reception. Accurate tuning is accomplished through the use of a slide rule megacycle drum dial and a vernier kilocycle dial calibrated in 1 kc increments. The passband tuning feature is accomplished by gang tuning the BFO and variable frequency oscillator using a metal belt. A "Q" multiplier stage is used to provide a tunable notch to minimize heterodyne interference. Separate detectors are used for AM and CW-SSB. An adjustable noise limiter is incorporated for AM and CW operation. A built-in 100 kc crystal calibrator is included as standard. Other options include an external cabinet mounted speaker (270G-2).
160 Meters: 1.5 - 2.5 Mc
80/75 Meters: 3.2 - 4.2 Mc
40 Meters: 6.8 - 7.8 Mc
20 Meters: 14.0 - 15.0 Mc
15 Meters: 20.8 - 21.8 Mc
11 Meters: 26.5 - 27.5 Mc
10 Meters: 28.0 - 29.0 Mc
10 Meters: 29.0 - 30.0 Mc
AM, CW, SSB
TYPE OF SERVICE:
Fixed Station operation.
115 vac, 50-60 cycles.
IMAGE AND SPURIOUS REJECTION:
Image ratio at center of each band is 50 dB or better. IF rejection at center of each band is 70 dB or better.
100 kc crystal oscillator (standard).
Warm-up drift is less than 300 cycles after 15 minutes of operation. Temperature stability is less than 1200 cycles drift from 0 to +/- 60 degrees C. Dial accuracy is 300 cycles after calibration.
1.0 microvolt for 6 db signal-to-noise ratio with 3 kc bandwidth.
Audio Output rise is less than 3 db for inputs of 5 to 200,000 uv.
AVC Time Constants: rise time = .01 second; release time = .1 second (fast); release time = 1 second (slow).
VARIABLE FREQUENCY OSCILLATOR:
70E-24 permeability tuned oscillator (PTO).
AUDIO OUTPUT LEVEL:
.75 watts with a 3.0 uv signal, 30% modulated.
Response: +/- 3 db 100 cps to 5000 cps.
Distortion: Less than 10%.
AUDIO OUTPUT REQUIREMENTS:
Speaker: 3-4 ohms / 500 ohms.
Fuse in ac line.
Receiver: 10 1/2" high x 17 1/4" wide x 15 1/2" deep.