Murphy Radio, Welwyn Garden City, Hertfordsh., England

B40 C Admiralty Pattern 571403 / 57140C

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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

After World War II, Murphy did develop a shortwave naval communications receiver to replace the B28 marine receiver.
The B40 naval receiver has a peculiar design: the dial arrangement with five horizontal illuminated waveband dials behind a curved glass looks like a spiral staircase of an English mansion dating from the thirties or like a lighthouse, so the B40 os often referred as lighthouse receiver.

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 CW HIGH and LOW for CW reception with two different settings of the NFO beat note. 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.

The Murphy B40 is a very peculiar set, a real "boatanchor" rarely seen "on the continent" and even rarer seen in Switzerland. It's a collectors set which still can be used as a secondary receiver for shortwave DXing.

The receiver exists in five variants:
Model No. /
Admirality Pattern
B40 Prototype
Model designation engraved in the cover above the frequency dials
Reception modes CAL, R/T, Tune system, CW high/low, listen through
Blocking of the main tuning knob at the left below the knob.

Model designation moulded in cast cover above the frequency dials.
Reception modes CAL, R/T, Tune, CW high/low.
Speaker switch at the left below the speaker grill.
Mechanical modifications to improve servicing, high quality components used.
Model designation tag mounted with screws on the cover above the frequency dials,
Improved tuning mechanism, crystal filter.
AGC switch at the left hand below the speaker, speaker switch above the mains switch.

Model designation tag mounted with screws on the cover above the frequency dials,
AGC switch at the left hand below the speaker, speaker switch above the mains switch.
Improved R.F. circuitry to enable several receivers beeing used on one aerial.

Model designation tag mounted with rivets on the cover above the frequency dials,
Reception modes CAL, R/T, Tune, FSK narrow CW high/low und FSK wide high/low
Additional Oscillator Trim control at the left just below the CRYSTAL switch.
Valve layout altered (additional rectifier, valves from EF9x series).

Similar receivers with different frequency coverage

Model No. /
Admirality Pattern
B41 VLF Variant: 15 - 700 kHz
Model designation casted in the cover on top of the frequency dials, Lettering printed on the front panel.

B41 VLF Variante: 15 - 700 kHz
Model designation tag mounted with screws on the cover above the frequency dials,
the lettering for the controls is realised with tags mounted with small screws.

62B VLF / HF All wave - Variant: 150-1500 kHz, 3,9-30,5 MHz.
Model designation tag mounted with screws on the cover above the frequency dials,
AGC switch below the speaker grill, speaker switch above the mains switch.

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