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Hammarlund Mfg. Co., New York / Mars Hill NC

SP - 600 - JX / Super Pro SP-600

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überarbeitet am 14.11.2010

Double conversion (above 7 MHz), I.F. (3955) / 455 kHz

Analog dial, bandspread dial witch mechanically coupled log dial

AM, CW with BFO

Sensitivity < 0,75 uV CW, < 2 uV AM

Selectivity (- 6 dB)
0,2 / 0,5 / 1,3 (crystal)/ 3 / 8 / 13 kHz

RF gain, bandspread dial, crystal phasing / notch filter

The Super Pro / SP-600 is the latest and last model of Hammarlund's Super Pro series, it has been produced from 1951 until 1961 in numerous variants for the military and civil market.

The receiver is a veritable "Boatanchor", the version with the desktop cabinet is 55 x 32 x 44 cm wide and has a weight of 39,4 kg and the rack version 48 x 26,6 x 44 cm wide has a weight of not less then 30 kg. The receiver can be powered from different voltages from 90 - 270 V and 50-60 Hz, some J versions even with 25 - 60 Hz, power consumption is around 130 Watts.

Fontpanel SP-600
In the centre of the frontpanel, You find the two dial windows. A mechnically moved pointer (looks like a sharpened pencil) points to the active dial on the left main tuning dial, it is moved by the band selector knob just below. The right dial is the fine tuning dial of which only the active part is visible through a small aperture. Both dials are coupled mechanically, the set is tuned from the main tuning knob below the right bandspread and logging dial. The dial accuracy of the main dial is around 25 kHz in the 49 m band and on worse on higher frequencies, e.g. around 50 - 100 kHz in the 19 m band. The tuning lock knob locks the tuning mechanism mechanically.

The receiver's main switch is mechanically coupled to the RF gain control, this will let You manually adjust the high frequency amplification, at least if thw AVC switch in the right lower corner is in the MAN(ual) position. The volume control is located in between the band selector and the main tuning knob.
At the right side, below the loggind dial, You find the knob to activate the BFO for CW reception, the beat note can be adjusted with the BEAT OSC control and the AGC speed is adapted for CW reception.
Above the RF gain and the BFO control, You find on the SP-600 variants with the suffix "X" a switch for six crystal controlled channels for fixed frequency operation, a DeltaF control permits to detune the receiver slightly to avoid interference on the standard fixed frequency channel. The quartz frequency should be the desired frequency + 455 kHz in the frequency ranges 2 and 3 and one third of the sum (reception frequency + 3955 kHz).br /> At the same place, You find a control to adjust i.f. amplification in the SP-600-J-4 / R-320A variants of the receiver.

In the left lower corner of the front panel, You find the switches for TRANSMIT / RECeive operation, the headphones jack and the noise limiter, the receiver has no internal speaker.
The controls SELECTIVITY and PHASING are used to select the different i.f. bandwiths and activate the crystal filter in the three narrow i.f. bandwidths, the XTAL PHASING control is used to eliminate an interfering signal like a notch filter. A little switch sets the round meter to signal strength and audio level display

Blockschaltbild SP-600

The R.F. signal coming from the antenna is amplified in two stages (V1 and V2, 6BA6, 6BA6), in the first mixer (V5: 6BE6), it will be mixed with the signal from the crystal oscillator (V3: 6AC7) for fixed frequency operation or from the VFO signal (V4: 6C4) to generate the intermediate frequency of 455 kHz in bands 1 - 3, which will be amplified (V7: 6BA6). In bands 4 and 5m the resulting first intermediate frequency 3955 kHz will me mixed with a 3,5 MHz oscillator signal (V8: 6C4) in the second mixer (V6: 6BE6) to end with the same intermediate frequency of 455 kHz.
After having passed the i.f. filters, the signal has to pass two amplifier stages (V9: 6BA6 / V10: 6BA6) and will fed after a driver stage (V11: 6BA6) the demodulator stages. Here, the AGC signal is generated (V14B: 1/2 6AL5) and in some variants, the i.f. is amplified to feed an i.f. output connector (V16A: 1/2 12AU7) at the rear face of the receiver.
The second system of V14A (1/2 6AL5) acts as a diode demodulator, the BFO signal (V13: 6C4 / amplifier V12: 6BA6) is added here for CW reception.
A portion of the signal will drive the noise limiter (V15A: 1/2 6AL5), the remaining signal will be fed to the audio frequency preamplifier (V16B: 1/2 12AU7) and final stage (V17: 6V6GT).
The V15B (1/2 6AL5) acts as recifier to display the a.f. signal level on the meter. The R.F. gain control acts on the grid voltage of V20 (6AL5).
In the power supply V19 (5R4GY) acts as rectifier tube, V18 0A2 as voltage stabiliser.
There is a extensive description of all receiver circuits in TM 11-851.

The typeplate is usually found on the cover of the r.f. unit: J- will say that all components meet the JAN (Joint Army Navy) Standard requirements, a X that the receiver is equipped with an oscillator for crystal controlled fixed frequency operation, and a L, that the set covers not the mediumwave band but the longwaves, used in the United States for aeronautical beacons (NDB). Find further informations about the different SP-600 variants based on the excellent survey made by Les Locklear > > > here < < <.

© Martin Bösch 28.4.2008 / transl. 15.11.2010

weitere Lektüre:
e: Osterman, F.: Shortwave Receivers - Past and Present