Manufactured by Collins Radio Comp., Cedar Rapids.

I got my Collins 51J-4 S/N 1601 from Walter K., it had been unused for years and stored in a dry warehouse.

The receiver had been used by Swiss PTT, which is indicated by a sticker. The set is wired for 220 V operation, years ago a modification was made by installing a switch for the loudspeaker in place of the loudspeaker socket.

• Principle: double/triple conversion superhet, IF 1.5-2.5 or 2.5-3.5 MHz, 500 kHz
• Operation modes: A1 with BFO, AM (A3)
• Frequency range: 0.5 - 30.5 MHz
• Frequency display: linear analogue display, 1 kHz reading accuracy
• Frequency memory: none
• Signal strength indicator: S-meter
• Signal processing: RF gain, AGC, noise limiter, crystal filter
• Features: crystal calibrator 100 kHz
• Sensitivity: AM (A3) <5 μV / Selectivity: 1.5/4 kHz, 3 / 8.5 kHz, 6 / 14.4 kHz (-6/-60 dB)

• Mains operation: 110, 220 V

• 536 x 317 x 333 mm, weight 28.5 kg (without cabinet 21.3 kg)

By loosening the eight screws on the front panel, the set can be pulled out of the table cabinet, the table cabinet with the large cut-out at the rear allows the upper cover to be pulled out and is original to the 51J-4.

After loosening three wing nuts, the upper metal cover can be removed, the chassis is clean, the adjustment tool for the PTO is present in its holder. The angled Philips screwdriver on the back of the receiver and the four Allen keys for removing the buttons in their holders on the inside of the cover plate are also included.

The PTO is the 70E-15 version belonging to the 51J-4 with the CR suffix; with this improved PTO the problems with the uncorrectable error at the scale end points (EPE) do not occur, the display of the receiver can practically always be set to the correct frequency.

Next to the PTO under a retaining bracket are the three mechanical IF filters in their angular metal cabinets.

The backing paper of the coarse dial for the 1 MHz ranges has become brittle and should only be touched with great care.

The set is slowly powered up with the regulating isolating transformer and the dial illumination and tubes begin to glow. Without developing smoke or odour, 220 V is reached, a note on the back states that the set has been wired for 220 V for use in Switzerland (otherwise be careful applying a tension higher then 110 V if it might be an original U.S. set).

Some noise can be heard from the connected loudspeaker, after pressing the MHz wave switch this becomes quieter, sometimes it crackles and reception stops.

The first step is to clean the contacts of the wave switches, which are activated via the gearbox when the 1 MHz wave switch is turned and which sometimes turn to the left and sometimes to the right, after applying Deoxit-5 and turning the wave switch a few times, they always engage properly.

The check shows that there is now stable hiss on all ranges and the day is saved.

The contacts on the other switches and pots are now maintained with a little Ballistol and the volume control now also works without any problems or crackling.

The function can be checked with the built-in crystal calibrator, the dial can be calibrated with the adjustable pointer and the antenna can be optimally adjusted with the antenna trimmer. Now it's time for a quick trip through the shortwave bands, which are pretty empty in the morning hours.

I find what I'm looking for in the 19 m band and can listen to an American radio preacher (WMLK) on 15150 kHz, otherwise the band is quiet in the morning hours.

The SMFP is now used to test the receiver. The automatic test with the 6 MHz filter gives back a sensitivity of 2, 4 and 7 μV for 10 dB SN/N on 15, 9 and 6 MHz. This corresponds to the specifications in the manual, but I am used to a slightly better sensitivity from the 51J-4, so it might be time for a tube test and alignment - for now, the set is running well after years of storage.

V001 and V002 (6BA6, VFO 2-3 MHz ); V101 (6AK5, RF preamplifier); V102 (6BE6, 1st mixer to 2.5 → 1.5 MHz ); V103 (6BE6, 2nd mixer, Band I); V105 (6AK5, 12 MHz oscillator); V106 (6BE6, 3rd mixer to 500 kHz) V301 (6BA6, 1st IF amplifier 500 kHz); V302 (6BA6, 2nd IF amplifier 500 kHz); V108 (6BA6, 3rd IF amplifier); V109 (6BA6, 4th IF amplifier); V110a (12AX7, detector); V112b (12AX7, Noise Limiter); V112a (12AX7, AF preamplifier); V113 (6AQ5, audio final amplifier) V110a (12AX7, 1st AGC amplifier); V111a (12AU7, 2nd AGC amplifier; V111b (12AU7, amplifier 500 kHz IF output; V104 (6BA6, calibrator); V114 (6BA6, BFO)
V115 (5V4G, mains rectifier), V116 (0A2, voltage stabilizer).

* 51J-4 Communications Receiver, Instruction Book, Collins Radio Comp.

* Collins 51J-4 on the website of www.radiomuseum.org * excellent information on the 51J-4 at radioblvd.org or the Western Historic Radio Museum of Henry Rogers