K5AM - Collins 51J-4 receiver K5AM       Boatanchor collection      
Collins 51J-4 receiver


Serial number 1938.
Three original Collins mechanical filters, 1.4, 3.1, 6.0.
Matching cabinet.

History.
1957-1963. Approximate date of manufacture.
Manufacturer: Collins Radio Company, Cedar Rapids, Iowa.
Original cost: $1200.00 .. $10,300.00 in 2016 dollars.
Cabinet was an optional extra. Three mechanical filters were optional extras.
December, 1996. Purchased by K5AM.
January, 1997. Complete check-out, alignment, and lube.
1997-2016. Installed on boatanchor bench in shack.

Modification.
Replaced 2 conductor line cord by IEC AC receptacle, 3c, including ground. (Line cord included.) This is safer, and an excellent improvement, not to have a dangling line cord to deal with when moving the receiver.

Test results; November, 2016.
HP 8640B, HP 3400A(true RMS).
Sensitivity test A, each band. Results well within specifications, without taking time to measure exact MDS on each of 30 bands. Specifications, for 10 dB S+N/N, conditions not stated: Band 1, 15 V; Bands 2-30, 5 V.
      Measurements, SSB/CW, 1 kc filter:
           Band 1 (0.5-1.5 mc): MDS -121 dBm (0.2 V).
           Bands 2-30: better than MDS -130 dBm on each band.
      Results: excellent.
Sensitivity test B, exact measurement for each filter, SSB/CW.
Frequency(mc), Bandwidth(kc), MDS(dBm).
     28.050, 1, -133.
     28.050, 3, -131.
     28.050, 6, -128.
Results: excellent.
Sensitivity test C, AM. Test conditions: 3880 kc, BW 6 kc, 60% modulation, 10 dB S+N/N.
     Measurements:
          400 cps, 0.45 V
          1000 cps, 0.50 V
     Results: excellent.
AM THD test; HP 8640B, HP 334A. Specs: less than 10% distortion at 0.5 watt output (conditions not specified). Test conditions: 0.5 watt into 8 ohms, 10 mc, BW 6 kc, 50 V, 60% modulation.
     Measurements:
          400 cps, 5.4%
          1000 cps, 4.2%
     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