Manufactured by Hammarlund Mfg. Co., New York NY.

The SP-600 was produced over several years in a big number of variants. For an overview of the variants, see the table in „Shortwave Receivers Past & Present“ by Fred Osterman or the original version of the list compiled by Les Locklear at www.hammarlund.info.

• Principle: Double conversion (above 7 MHz), IF (3955) / 455 kHz
• Operation modes: A1 with BFO, AM (A3)
• Frequency range: mostly 0.54 - 54 MHz
• Frequency display: Analogue dial, 25 - 50 kHz
• Frequency memory: none, some variants with six crystal controlled frequencies
• Signal strength indicator: S-meter
• Signal processing: RF gain, crystal phasing - notch filter
• Features: band spread
• Sensitivity: AM (A3) < 2 μV, CW < 0.75 μV / Selectivity: 0.2 / 0.5 / 1.3 (crystal)/ 3 / 8 / 13 kHz (-6 dB)

• Mains operation: 110, 220 V

• Rack version: 480 x 266 x 440 mm, weight 30 kg

On the nameplate, which can be found on the cover of the HF unit, a J means that components according to JAN (Joint Army Navy - Standard) are installed, an X that crystal controlled frequencies can be selected and an L that the set covers the long-wave range (used for aircraft beacons in the USA) instead of the full medium-wave coverage.

SP-600-JX-1	frequency coverage 540 kHz - 54 MHz		Army designation R-274A/FRR	component of the AN/MRR-4; GRC-38A & B systems
SP-600-JLX-2	Frequency coverage 100-400 kHz & 1.35-29.7 MHz
SP-600-J-3	Frequency coverage 540 kHz - 54 MHz	no crystal controlled frequencies
SP-600-J-4	Frequency coverage 540 kHz - 54 MHz	no crystal controlled frequencies, separately adjustable IF gain	Army designation R-320A/FRC	component of the OA-58B/FRC
SP-600-J-5	Frequency coverage 540 kHz - 54 MHz	no crystal controlled frequencies, AC operation 25 - 60 Hz	Army designation R-483/FRR
SP-600-JX-6	Frequency coverage 540 kHz - 54 MHz	BFO range +/- 10 kHz	Navy designation R-274B/FRR	Component of AN/MRR-4; GRC-38A & B
SP-600-JX-7	Frequency coverage 540 kHz - 54 MHz
SP-600-JX-8	Frequency coverage 540 kHz - 54 MHz		produced for Welch Contract. XG-479
SP-600-JL-9	Frequency coverage 100-400 kHz & 1.35-29.7 MHz	no crystal controlled frequencies
SP-600-JX-10	Frequency coverage 540 kHz - 54 MHz		Successor model of the SP-600-JX-7
SP-600-J-11	Frequency coverage 540 kHz - 54 MHz	no crystal controlled frequencies	Successor model of the SP-600-J-3
SP-600-JX-12	Frequency coverage 540 kHz - 54 MHz		Signal Corps designation R-274A/FRR	Successor model of the SP-600-JX-1
SP-600-J-13	Frequency coverage 540 kHz - 54 MHz	no crystal controlled frequencies, AC operation 25 - 60 Hz	Successor model of the SP-600-J-5
SP-600-JX-14	Frequency coverage 540 kHz - 54 MHz		Signal Corps designation R-274C/FRR (R-542/FRR)	Successor model of the SP-600-JX-10
SP-600-JLX-15	Frequency coverage 100-400 kHz & 1.35-29.7 MHz		Successor model of the SP-600-JLX-2
SP-600-JL-16	Frequency coverage 100-400 kHz & 1.35-29.7 MHz	no crystal controlled frequencies	Successor model of the SP-600-JL-9
SP-600-JX-17	Frequency coverage 540 kHz - 54 MHz	Diversity receiver, recognisable by two red buttons	produced for the Air Material Command
SP-600-JX-18	Frequency coverage 540 kHz - 54 MHz		Produced for GAUVREAU Contract	Follow-up model of the SP-600-JX-10
SP-600-J-19	Frequency coverage 540 kHz - 54 MHz	no crystal controlled frequencies, AC operation 25 - 60 Hz	Successor model of the SP-600-J-13
SP-600-J-20	Frequency coverage 540 kHz - 54 MHz	no crystal controlled frequencies, AC operation 25 - 60 Hz, 90 - 270 V	Signal Corps designation R-483A/FRR	Successor model of the SP-600-J-19
SP-600-JX-21	Frequency coverage 540 kHz - 54 MHz		Follow-up model of the SP-600-JX-10 & SP-600-JX-14
SP-600-J-22	Frequency coverage 540 kHz - 54 MHz	no crystal controlled frequencies	Follow-up model of the SP-600-J-11
SP-600-JLX-23	Frequency coverage 100-400 kHz & 1.35-29.7 MHz		Successor model of the SP-600-JLX-15
SP-600-JL-24	Frequency coverage 100-400 kHz & 1.35-29.7 MHz	no crystal controlled frequencies	Successor model of the SP-600-JL-16
SP-600-J-25	Frequency coverage 540 kHz - 54 MHz	no crystal controlled frequencies, AC operation 25 - 60 Hz	Successor model of SP-600-J-19
SP-600-JX-26	Frequency coverage 540 kHz - 54 MHz		Signal Corps designation R-274C/FRR	Successor model of SP-600-JX-14 & SP-600-JX-21
SP-600-JLX-27	Frequency coverage 200-400 kHz & 540 kHz -29.7 MHz
SP-600-JX-28	Frequency coverage 540 kHz - 54 MHz		Signal Corps designation R-620/FRR
SP-600-JX-29	Frequency coverage 540 kHz - 54 MHz		for CIA, Contract No. XG-1178
SP-600-JX-30	Frequency coverage 540 kHz - 54 MHz	Diversity receiver, recognisable by two red buttons	Successor model of the SP-600-JX-17
SP-600-VLF-31	VLF frequencies 10 - 540 kHz	4 crystal controlled frequencies
SP-600-JX-32	Frequency coverage 540 kHz - 54 MHz	black front panel with engraved designations		produced for Mackay Radio, technically identical to SP-600-JX-21
SP-600-JLX-33	Frequency coverage 100-400 kHz & 1.35 - 29.7 MHz
SP-600-JL-34	Frequency coverage 100 - 200 kHz, 540 KHz - 14.8 MHz		for CIA, Contract No. XG-1765
SP-600-JX-35	Frequency coverage 540 kHz - 54 MHz	BFO range +/- 10 kHz	Signal Corps designation R-274B/FRR
SP-600-JX-36	Frequency coverage 540 kHz - 54 MHz	technically identical to SP-600-JX-21, additional audio input on the rear side	produced for FBI under No. FBI-16876
SP-600-JL-24 „Special“	Frequency coverage 100 - 200 kHz, 1.35 - 29.7 MHz		US Navy designation R-274B/FRR
SP-600-JX-37	Frequency coverage 540 kHz - 54 MHz	AC operation 25 - 60 Hz	Successor model of the SP-600-JX-21
SP-600-VLF-38	VLF frequencies 10 - 540 kHz	4 crystal controlled frequencies, AC operation 25 - 60 Hz
SP-600-JX-39	Frequency coverage 540 kHz - 54 MHz		produced for FAA Contract FA-2338
SP-600-JX-21A	Frequency coverage 540 kHz - 54 MHz	latest variant of the SP-600 with product detector (LSB/USB/CW MOD switch)	front panel with engraved labelling & the designation JX-21A