Murphy Radio, Welwyn Garden City, Hertfordsh., England

B40 D Admiralty Pattern 571404 / 57140D

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überarbeitet am 21.10.2010

Single conversion superhet, I.F. 500 kHz

Analog dial,


640 kHz - 30,6 MHz

Selectivity -6 dB
1 / 3 / 8 kHz

CW <2 uV

Noise Limiter,

1 fixed frequency with plug-in crystal

The Murphy receiver B40 has been developed for the British Navy after 1946, it's characteristic backlit dials gave the set it's nickname "lighthouse receiver" or "spiral staircase radio". The set has been improved in the fifties, filters and a fine tuning option to make it ready for FSK (radioteletype) reception.

The shape of the receiver with it's height is quite unique, the width of the receiver is a bit smaller then 19 inch, two heavy duty screws keep the front panel and chassis in place it the heavy metal cabinet.
The mains cable is connected to the receiver with a screwed two pin connector typical for British naval communications sets.
The antenna socket, as well in a quite unique norm, a 600 ohms audio frequency connector, the main speaker switch (must be set to face towards the front front panel, if no external speaker is connected), an I.F. connector and a screwdriver operated dial illumination dimmer can be found at the rear upper part of the receiver.

The frontpanel has three sections, the middle part looking like a column with the illuminated "spiral staircase" dial and the main tuning knob, a right and a left panel with the controls.
At the left, You find the internal monitor speaker behind five wholes as protection cover, just below two switches for A.G.C and the noise limiter and a control for noise limiter intensity. The next two big knobs are the bandwidth selector (standard bandwidths are 1 kHz, 3 kHz and 8 kHz) and the modes switch. The modes are CAL (a crystal calibrator, the calibration mechanism to adjust the dial is found behind the "door" at the top of the frequency dial, the bit carrying the "B 40" label. Position R/T is used for normal reception, TUNE will add a internal carrier to help You tuning in a station (the carrier is correctly tuned when tuned to zero beat), and the positions FSK NARROW / CW HIGH and LOW for CW reception with two different settings of the NFO beat note and FSK-WIDE HIGH and LOW for FSK reception.
FSK is a radio teletype protocol based on signals transmitted on two adjacent frequencies with a well determined distance, the so called shift distance. The two tone Baudot code is used - a code system similar to ASCII code. The BAUDOT code only supports capital letters and a special code is used to switch over to numbers instead of letters. To decode the message, the output of the receiver is fed to a FSK converter (this will accept signals of a certain frequency and shift) and will drive a mechanical teletypewriter. The OSC TRIM only found on B40 D series is used to shift the note of the radioteletype signal to the exact frequency used by the FSK converter.
The volume control is the small knob labelled A.F. gain between the two big ones. Further below, there are the switches for the internal speaker and the mains switch as well as the mains power cable connector.
In the right front panel section, You find a crystal compartment with an internal heater for high frequency stability when receiving on a fixed frequency with a plug in crystal (desired reception frequency - 500 kHz), when fixed frequency mode is "ON", the compartment and the "X" is illuminated with a red light. The knob "ANTI-CROSS MOD(ulation)" acts on the grid voltage of the first R.F. amplifier, for normal use, this should be on the maximum position. With the BAND SWITCH, You activate the massive band selector, the dial light will move to the corresponding dial to indicate, which band is active. Just below is the R.F. gain control and the headphones socket.
In the middle, You find the frequency dials behind a curved transparent protector, the dial of the active frequency band is backlit, a small black triangle in the middle acts as dial pointer and the complete dial is rotating when the set is tuned. Below, just above the massive tuning knob, You find a 0 - 100 logging dial, this will give You the possibility to find a station on a known frequency again, when You have written the setting of the logging scale in the station's logbook. The lever of the dial lock mechanism is very rugged (it has a feeling like a gear lever of a sports car) and the dial lock lever can be blocked in the LOCK position by means of a knurled screw.

The location of the controls spread on the front panel is a bit odd, but this is not the only British set with controls spread over the frontpanel in a peculiar way... Use the bis MAINS switch in the left lower corner of the front panel to switch on the set, the speaker switch LS should be on ON, the modes switch on R/T (for radiotelephony) and the BANDWIDTH switch on 8 kc/s. Turn the band switch to band No. 3 and search for stations from the 49 m shortwave broadcast band in the region of the 6 MHz mark. ANTI CROSS-MOD. and (R.F.) GAIN should both be in the full clockwise position, use the tiny A.F. GAIN at the left to control the volume (I first thought, this tiny knob might be the line level gain control, not the main volume control).

This single conversion set with an intermediate frequency of 500 kHz gives You fair - good results on the shortwave bands, the sensitivity is sufficient to catch international shortwave broadcasters in good quality and also some marine and amateur radio CW communication.
Because of the non-linear dial, searching for a signal of a station with a known frequency is not easy, especially in the high frequency bands, where frequency marks are quite coarse.
The receiver is constructed in a very solid way and should remain on a selected frequency with the dial LOCK on very stably; even if the D version was meant for FSK (radioteletype) reception, I have not tried operation with a FSK converter. I qould rather rely on a stable PLL based receiver for this purpose.
Just in case, someone has a matching FSK converter for sale, let me know, I might give it a try.

The Murphy B40 D is a very peculiar set, a real "boatanchor" rarely seen "on the continent". It's a collectors set which still can be used as a secondary receiver for shortwave DXing, but for everyday use, radioteletype decoding with a matching converter and a teletypewriter it is obsolete...

Further literature:
e: Osterman, Fred: Receivers Past & Present, Universal Radio Research, Reynoldsburg, OH 43068, USA, ISBN 1-882123-07-7
e: Murphy B40 series of Naval Communications Receivers
d/e: Murphy B40 at www.radiomuseum.org

© Martin Bösch 10.7.2010