Hammarlund SP-600 JX-6 [RADIO]

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Egon van Kampen restored this beautiful sept 1951 Hammarlund SP-600 JX-6 (serial# 69/03) shortwave radio receiver.

In a Youtube comment user Willow Slough wrote:
This is one of the best tube SW receivers ever built.  BFO is superb. All Hammarlund SP-600s which include the letter "J" in the nomenclature were built to military specifications, whether they had a military contract tag or not. Speaker audio from a stock SP-600 will not cut off if headphones are plugged in. None of the SP-600 RF/AF meters were illuminated. Hammarlund opted for a better sealed meter rather than illumination. The crystal selectivity positions were intended primarily for CW and RTTY reception but they are very useful for tuning other signals as well.  VFO is the normal operation position. The XTAL positions 1-6 are each controlled by a crystal for individual and extremely accurate (for the day) frequency control of six specified frequencies. The delta change knob above the BFO knob adjusts XTAL frequency setting, not the BFO which is extremely accurate when correctly aligned. Nonetheless, the Band Change and Tuning knobs had to be properly set for best performance from the XTAL controlled frequencies. This feature was designed for RTTY use. SP-600 is excellent for SSB and ECR reception but the radio must be properly operated for MANUAL (not AVC) reception and you must ride the RF gain manually. Designed specs for the SP-600 can only be achieved with an accurate IF and RF alignment. The military Technical Manuals for maintenance and alignment of this radio are available free on the internet.

The Hammarlund Historian web page went offline a few years back. In 2014 a few volunteers worked to salvage it but finally gave up in 2014. I was able to retrieve some information using the Wayback Machine.

Les Locklear made this overview of models and serial numbers:


PRODUCTION DATE SUFFIX # NOTES
Sept. 1951 SP-600-JX-1 Std. Frequency range 540 khz-54 MHz. Also designated R-274A/FRR ("Fixed Radio Receiver") Signal Corps order no. 1689-Phila- 51-01. Note: many early SP-600's were simply designated SP-600-JX
Sept. 1951 SP-600-JLX-2 Frequency range 100-400 khz, 1.35-29.7 MHz
Sept. 1951 SP-600-J-3 Std. Frequency range, 540 khz-54 MHz. No X-tal frequency control.
Sept. 1951 SP-600-J-4 Std. frequency range, 54O khz-54mhz. No X-tal frequency control. Equipped with 25 to 60 cycle ( hertz ) power supply. Signal Corps. R-320A/FRC, order no. 21478-Phila-50-06. Also has separate IF gain control located where the X-tal frequency control was normally located. Part of OA-58B/FRC Set.
Sept. 1951 SP-600-JX-6 Std. Frequency range, 540 khz-54 MHz. BFO range 0-10khz. U.S. Navy model R-274B/FRR, order no. Nobsr-52039 19 October, 1954. Navships manual 91661.
Sept. 1951 SP-600-JX-7 Std. frequency range, 54O khz-54mhz.
Sept.1951 SP-600-JX-8 Std. frequency range, 54O khz-54 mhz. Manufactured for Welch contract no. XG-479. Believed to be a cover for a CIA contract.
Sept. 1951 SP-600-JL-9 Frequency range, 100-400khz, 1.35-29.7 mhz. No X-tal frequency control.
Nov. 1951 SP-600-JX-10 Std. frequency range, 54O khz-54 mhz. Replaces JX-7.
Nov. 1951 SP-600-J-11 Std. frequency range, 54O khz-54mhz. No X-tal frequency control.Note: This model made to complete NAVY order, without the changes per ECN1156 as standard J series. Replaces J-3.
Nov. 9, 1951 SP-600-JX-12 Std. frequency range, 540 khz-54mhz. Signal Corps. R274A/FRR, order no. 3376-Phila-52. Replaces JX-1.
Nov. 26, 1951 SP-600-J-13 Std. frequency range, 54O khz-54mhz. No X-tal frequency control. Signal Corps. order no. 16838-Phila-51. Serial no's. 52 to 67 inclusive. 25 to 60 cycle power supply. Replaces J-5. 16 receivers produced on this order.
April 23, 1952 SP-600-JX-14 Std. frequency range, 54O khz-54mhz. Signal Corps. R274C/FRR, order no. 3376-Phila-52. Also designated previously as R-542/FRR. Replaces JX-10.
June 17, 1952 SP-600-JLX-15 Frequency range, 100-400 khz, 1.35-29.7 mhz. Replaces JLX-2.
June 17, 1952 SP-600-JL-16 Frequency range, 100-400 khz, 1.35-29.7 mhz. No X-tal frequency control. Replaces JL-9.
June 17, 1952 SP-600-JX-17 Std. frequency range, 54O khz-54mhz. Diversity receiver. Manufactured for Air Material Command. Note: easily identified by 'red metal knobs'. The most common of the SP-600 series receivers.
June 26, 1952 SP-600 JX-18 Std. frequency range, 54O khz-54mhz. Made for ' GAUVREAU ' contract. Replaces JX-10.
Aug. 27, 1952 SP-600-J-19 Std. frequency range, 54Okhz-54 MHz. No X-tal frequency control. Equipped with 25 to 60 cycle power supply. Replaces J-5, J-13.
Aug. 1952 SP-600-J-20 Std. frequency range, 54O khz-54mhz. No X-tal frequency control. Same as J-19. Signal Corps. R-483A/FRR, order no. 3479-Phila-52-05. Equipped with 25 to 60 cycle power supply. Replaces J-19.
Feb. 13, 1953 SP-600-JX-21 Std. frequency range, 54O khz-54mhz. Replaces JX-10.
Feb.1953 SP-600-J-22 Std. frequency range, 540 khz-54mhz. No X-tal frequency control. Replaces J-11.
Feb. 1953 SP-600-JLX-23 Frequency range, 100-400 khz, 1.35-29.7 mhz. Replaces JLX-15.
Feb. 1953 SP-60O-JL-24 Frequency range, 100-400 khz, 1.35-29.7 mhz. No X-tal frequency control. Replaces JL-16.
Feb. 1953 SP-600-J-25 Std. frequency range, 54O khz-54mhz. No X-tal frequency control. Equipped with 25 to 60 cycle power supply. Replaces J-19.
Feb. 1953 SP-600-JX-26 Std. frequency range, 54Okhz-54mhz Signal Corps. R274C/FRR, order no. 3376-Phila-52. Effective upon Signal Corps. approval of TAR#10 dated 2-12-53. Replaces JX-14.
March 13, 1953 SP-600-JLX-27 Special frequency range, 200-400 khz, 540 khz-29.7 mhz.
Oct. 5, 1953 SP-600-JX-28 Std. frequency range, 54O khz-54mhz. Signal Corps. R-620/FRR, order no. 25693-Phila-53-61, contract DA-36-039-SC-49453, 100 units built, s/n 15001-15100. Several ckt modifications.
March 12; 1954 SP-600-JX-29 Std. frequency range, 54O khz-54mhz. Made for CIA contract no.XG-1178.
Dec. 28, 1954 SP-600-JX-30 Std. frequency range, 54O khz-54mhz. Diversity receiver. Replaces JX-17 red metal knobs, not very common.
Dec. 1954 SP-600-VLF-31 Special frequency range, 10-540khz X-tal frequency control (4 position). Very low frequency receiver.
Dec. 1954 SP-600-JX-32 Std. frequency range, 540 khz-54mhz. Black wrinkle finish front panel with white engraved lettering. Made for Mackay Radio, their order no. M-41666, Hammarlund production order no. 2467- 300. Internally the same as JX-21.
Dec. 1954 SP-600-JLX-33 Special frequency range, 100-400 khz, 1.35 - 29.7 mhz.
Aug. 7, 1956 SP-600-JL-34 Special frequency range, 100-200khz, 54O khz-14.8 mhz. Made for CIA. Their order no. XG-1765.
Aug,. 1956 SP-600-JX-35 Std. frequency range, 540 khz-54mhz. X-tal frequency control. BFO range 0-10 khz. U. S. Navy R-274B/FRR, order no. NObsr-71369. Navships manual 91661.
Oct. 3, 1957 SP-600-JX-36 Std. frequency range, 540 khz-54mhz. X-tal frequency control. Made for FBI, their order no. FBI-16876, their contract no. J-FBI-3873. Same as JX-21, except for addition of audio input jack on rear of chassis.
Oct. 9, 1957 SP-600-JL-24
( Special ) 		Frequency range, 100-400 khz, 1.35-29.7 mhz. No X-tal frequency control. U.S. Navy R-274B/FRR. Supplied to NAVSHIPS 91661, R-274B/FRR per PL-33910-1. Reason for 'Special' designation not known.
Mar. 28, 1961 SP-600-JX-37 Std. frequency range, 540 khz-54mhz. X-tal frequency control. 25 to 60 cycle power supply. Otherwise, same as JX-21.
March, 1961 SP-600-VLF-38 Special frequency range, 10-540 khz. X-tal frequency control (4 position). Very low frequency receiver. 25 to 60 cycle (hertz) power supply. Same as VLF-31 except for 25 to 60 cycle (hertz) power supply.
July 21, 1961 SP-600-JX-39 Std. frequency range, 540 khz-54 mHz. Made for FAA contract no. FA-2338.
June 1969-1972 SP-600-JX-21A Std. frequency range, 540 khz-54 mhz. This was the last series of SP-600's manufactured. It had 22 tubes vs. 20 in other models. Also, a separate product detector, LSB,USB,CW,MOD switch. Appearance was different from other SP-600's in that the knobs had no metal skirts, the front panel was engraved with markings for Xtal phasing, selectivity, bfo, audio gain, rf gain. Also is marked JX-21-A on front panel. This is probably the rarest of the SP-600 series.

Also, check out the info to be found on sp-600.com such as the SP-600 Anthology Part 1, the SP-600 Anthology Part 2 and the SP-600 Models summary.

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