Practical Wireless

B40D Receiver, May 2021 issue


Dear Don,

This is a belated response to Philip Moss’s article on the B40 series of communicat­ion receivers used by the RN from the early 1950s till the early 1980s (although by that time most of them had been withdrawn and replaced by other types more suited to digital and microwave working).

I have disconnect­ed, lifted and shifted then repaired then shifted and lifted then reconnecte­d more than I want to remember. As the label states, they really do weigh 112lbs. They were also well designed so that only the mains power and headphone leads went in the front under the anti-shock and fixing tray. The antenna and AF output connection­s were at the rear top, protected by the raised outer casing. Also, being tall and narrow instead of wide and short, more receivers could be squeezed in the available space. The unitary constructi­on could be a pain at times, but at least it meant no turning the receiver on its head to replace a defective component. There are two variants of the

B40, the first being the B41, exactly the same build but with different IF frequency and tuning range from around 9kHz to 230kHz, just wide enough to bring in the BBC at 200kHz (now 198kHz, divisible by 9 for the for the new channelisa­tion of LF). This receiver was designed primarily for long-range reception and for the DX submarine broadcasts below 30kHz.

The second variant was the 62B, which covered all the BBC transmit frequencie­s (180kHz to 25Mhz) and was for entertainm­ent purposes having a slightly improved audio circuit and feeding into the SRE (sound reproducti­on system, a record deck and a set of 3 or 4 mixers). These days we carry all this around in our pocket on the mobile.

A word a warning is a good thing. If you have a B, C or D type and it has the black encased LF chokes and power transforme­r, beware. When the receiver doesn’t show any signs of life, and it is a supply problem, no dial lights, no hum from the loudspeake­r, etc. Just in case, wear a pair of elastic gloves (Marigolds) and a mask over mouth and nose (plenty of those around just now) and carefully remove the power and AF unit at the bottom. Examine the mains transforme­r and the smoothing chokes. If any of them show signs of the casing being bowed out, just a little or even a lot, look for oil on the chassis or if you are lucky, just seeping out from inside. Just look, do not touch or smell, get a large bucket or basin, place the power unit over the basin and let the oil run (drip) into the container. Also needed are a tough plastic bag and plenty of old rags, kitchen paper is too thin. Some of these inductive components were filled with oil that when heated turns into something rather less friendly. This oil and all the rags will have to be disposed of in a (possible) hazardous waste site. Your local council will have details of how and where.

I stated some, so you may escape. I cannot recall the name of the coolant oil, but there is no labelling on the casing to distinguis­h what is inside. The voltages and currents are all in the manual, and are also on the item as well, so it may be reasonably straightfo­rward to cobble up a replacemen­t power supply. I had this trouble, but on a different piece of gear. It took forever to get rid of the oil from the floor. I didn’t replace the transforme­r, just signed out for a new power pack!

Thanks for bringing back some memories. Dave Francis MM0DYX, ex-submariner Dunfermlin­e

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