Here I describe an American receiver from WWII, the Hammarlund Super Pro, which in the 200-X version was used in the allied air force ground stations. I also describe the SP-600-JX which was developed from the 200-X and is the version I have in my collection. The receivers are top class and were used by the military and other professional users.

Super Pro SP-200
Super Pro SP-600, my receiver
Photo Gallery


Oscar Hammarlund Oscar Hammarlund was born 1861 in Stockholm, Sweden. After completing technical college he went to work for the L. M. Ericsson Co., a leading manufacturer of telephones. Shortly he received an offer from USA and went there in 1882. After having worked for different American companies he eventually started his own business in 1910, mainly because of his interest in early wireless. He manufactured many different products, but the radio part of the business was not developing until the breakthrough of radio broadcasting some ten years later. Hammarlund manufactured radio components, and with Roberts he founded the Hammarlund-Roberts company to market receiver kits based on his components. A real success were his tuning capacitors, soon used in most US radio receivers.

Advertising the SP-200 The first superheterodyne shortwave receiver, the Comet Pro, was developed by Hammarlund and was first marketed in 1932. It sold in many thousands and was used by commercial operators, broadcast stations and radio amateurs. In 1936 came the first receiver in the famous Super Pro series, an enhanced Comet Pro, and in 1939 the Super Pro 200. This was built mainly for military and government users, and during the war it became the main receiver for the air force and navy ground stations. It had a push-pull output stage with as much as 14 watt power and very good sound quality, and was also sold to well situated radio amateurs and as a home receiver, see the advertisement from 1939. After many years of further development via the SP-400 came the legendary last model in the Super Pro series, the SP-600 in 1951. It was built in many variants until 1972.

After Oscar´s death in 1945 The Hammarlund Manufacturing Co. was headed by his son Lloyd. Beside receivers they delivered other kinds of advanced electronis to the military and the government, as well as mobile radio and Citizens Band radio. A popular series of amateur and shortwave listener receivers was the HQ series. The company had more than 2000 employees, but they could not adapt to the developing digital technique and the factory closed in 1972/1973. One of the most respected names in the history of radio manufacturing had come to an end! The Hammarlund receivers had an uncompromising choice of circuit technique and components, and they were very sturdy and easy to use.


During WWII the Super Pro 200-X was shipped to England in great quantities to be used in the air force ground stations. Receivers and control units for the transmitters were mounted in racks and many of these were used in each ground station to communicate with the aircraft, e. g. the English and American bomber armadas that flew in over Germany. The military designations for the receiver was BC-779-A/B (the most common), BC-794-B, BC-1004-C as well as R-129/U and R-270/FFR .

SP-200 operators The three most common variants of the SP-200-X (the X-model has a crystal filter in the IF stages), covers the frequency range 0.54 - 20 MHz, 1.25 - 40 MHz or 0.1 - 0.4 + 2.5 - 20 MHz. There is also a model without crystal filter. All models have 18 tubes, 16 in the receiver and 2 in the separate power supply. They are single supers with an IF of 465 kHz (not 455 kHz as in later models).
The selectivity is in addition to the fixed crystal filter positions variable from 3 to 16 kHz! The receiver has two RF stages, three IF stages, AVC, BFO, noise filter and AF stages with 14 watt output power. The sensitivity is specified to be 1.0 - 1.7 uV for 10 dB S/N. Band spread is used on all bands except 0.1 - 0.4 MHz.

The receiver is a really heavy one, mounted in a steel case it measures 54 x 32 x 39 cm (w x h x d) and weighs 33 kg + the power supply 26 kg!

In 1946 came the slightly improved model SP-400, which is not very different from the SP-200.


My SP-600 Data
My receiver is an SP-600, a more recent model which is built on the experience with the SP-200 / 400, it was manufactured 1951 - 1972. It is designed as a double super above 7.4 MHz to get better image rejection on higher frequencies. It has more modern miniature tubes and a rotating drum for the RF, mixer and oscillator coils, giving shorter leads between the coils, the 4 gang tuning capacitor and the tubes. The SP-600 has 2 RF stages and no less than 4 IF stages, one being the double super mixer. The front panel clearly shows the relationship with the SP-200 / SP-400.

Most variants of the SP-600 cover 0.54 - 54 MHz in six bands. The selectivity switch has six fixed positions, 0.2, 0.5 and 1.3 kHz (with crystal filter) and 3, 8 and 13 kHz at -6 dB. The intermediate frequencies are 3955 and 455 kHz. The flywheel tuning is very smooth, among the best ever made. Band spread is used on all bands with a fine scale marked 0 - 100. It is thus possible to log and return to stations with great accuracy. The receiver has no product detector for SSB reception, the exception being one of the last models made, the JX-21A, 1969-72. During the sixties an external SSB unit was made. The BFO is variable +-3 kHz from the front panel which makes it possible to receive SSB without a product detector.

Block diagram

The receiver has an internal power supply, the measures are 54 x 32 x 44 cm (w x h x d) but the weight is `only´ 40 kg. The receiver needs an external 600 ohm loudspeaker, or a 600 ohm 2 W resistor must be wired over the speaker output.

Capacitor formation Restoration
My receiver is the type SP-600-JX-21, manufacturing of this variant started in February 1953, it has serial number 20692. I bought the receiver from a collector in Södertälje, it was in a very good condition. As it has a high serial number it does not have the black decoupling capacitors known as "Black Beauty of Sudden Death", a series of short life capacitors that always have to be changed (more than 50!!) for the receiver to work properly.

After washing the case and vacuum cleaning the chassis I started the formation of the capacitors. As I do not have a variac I used a tap on the primary of an ordinary power transformer to decrease the input voltage, I also changed the receiver transformer tap to 260 V to reduce the voltages with around 40 %. I then cycled the receiver by switching it on for only 5 - 10 sec and let it rest for a couple of minutes, repeating this for an hour. I then increased the time switched on, first to 30 sec of 5 min a number of times, then to 1 min of 5 and so on until the receiver was switched on continously. The procedure took about 4 hours. No problems with capacitor overheating were found. The adjacent photo shows the receiver during the capacitor formation.

The receiver is like new inside and has very high sensitivity and good selectivity on all bands. All functions work well so the receiver does not need any restoration!

I also have a loudspeaker and a manual, these were probably not delivered with my receiver but they are contemporary. The speaker is a Signal Corps US Army SL-3, serial number 11991 manufactured by General Electric. The manual "General Purpose Communications Receiver Model SP-600-JX and Model SP-600-J Instructions" is Issue 6 released in May 1956. It has a stamp "Försvarsväsendets Radioanstalt Tekniska sektionen", crossed over and replaced by another stamp "Sveriges Meteorologiska och Hydrologiska Institut, Flygväderlekstjänsten Torslanda Göteborg - Flyg". In ink there is written "Inköpt 00 SMHI". This shows the type of professional institutions using these receivers! Many of the receivers imported to Sweden went to FRA for signal intelligence work.

My SP-600

My SP-600-JX-21.

SP-600 from above

Back right is the power transformer, in front of it the power choke and the fixed frequency crystal oscillator (without crystals)
to the left of the transformer is the rectifier tube.
In the middle is the screened tuning capacitor, to the right of it from front to back is the oscillator, first mixer,
second RF and first RF tubes and the antenna connector.
To the left are the IF stages, behind them the detector, AVC, AF driver and output stages.

Type plate Manual

The type plate and the manual.

Loudspeaker Loudspeaker type plate

The loudspeaker has been repainted and will be restored to original condition.


SP600J and JX Manual, SP-600 and valve data

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Updated October 24th 2009