K5AM       Boatanchor collection       Collins 75A-4 receiver • Serial number 2484. • Three filters; SSB, AM, CW. History. • 1955-1959. Approximate date of manufacture. • Manufacturer: Collins Radio Company, Cedar Rapids, Iowa. • Original cost: $595.00 . . .  $5100.00 in 2016 dollars. The two extra mechanical filters, 0.5 kc and 6.0 kc, were optional extras. • 1987. Purchased by K5AM. • 1987. Complete check-out, lube, and alignment. • 1987-2016. Installed on boatanchor bench in shack. Used routinely for on-the-air AM work with boatanchor transmitters. Modifications, 1987-1997. • Replaced two conductor line cord with safer three conductor cord, with ground. • Replaced C144 with high-quality silver mica, to protect filters. This is a crucial preventative measure, which every A-4 should have. • Replaced power supply filter capacitors. • Replaced all old, notorious "black beauty" capacitors, using high-quality modern components. Test results; November, 2016. HP 8640B, HP 3400A(true RMS), HP 5382A, HP 334A. • Collins specifications: for 6 dB SNR at BW 3 kc, 1 µV. Mode and other conditions not stated. • Sensitivity, SSB, BW 3.1 kc. Freq(kc), 6 dB SNR(µV), MDS(dBm)      1850, 0.13, -130      3800, 0.17, -130      7100, - , -127      14200, - , -130      21200, - , -125      28400, - , -131 Results: excellent. • Sensitivity, AM, BW 6 kc, modulation 1000 cps, 60%. Freq(kc), 6 dB SNR(µV)      1900, 0.10      3900, 0.11      29100, 0.10 Results: excellent. • Sensitivity, CW, BW 500 cps. Freq(kc), 6 dB SNR(µV), MDS(dBm)      1850, 0.13, -130      3550, 0.20, -135 Results: excellent. • Calibration test. Note that the front panel "zero set" allows adjustment for ±5 kc.      1) VFO linearity. Checked each 100 kc point; all within 1 kc.      2) HFO accuracy. Checked each band; all within 2 kc. Results: excellent. • Filter bandwidth test, -6 dB. Panel switch, filter nominal BW(cps), measured BW(cps).      A, 500, 472      B, 3100, 2839      C, 6000, 6067 Results: excellent. • Filter loss test. Panel switch, filter nominal BW(kc), receiver gain relative to SSB filter (dB).      A, 0.5, +1      B, 3.1, 0      C, 6.0, +6 Results: excellent. • AM THD test. Collins specs: less than 10% distortion, conditions not specified. Test conditions: 0.5 watt AF output into 8 ohms, 3.890 mc, 50 µV, BW 6 kc, modulation 1000 cps 60%.      Measured: 3.4% Results: excellent. • By-ear test, in speaker. Sounds great, SSB, CW, AM. Summary. An exceptionally fine specimen of a classic receiver. Mark, K5AM. www.zianet.com/k5am   home page     boatanchor page