This is a little known and quite rare B21b, admiralty pattern W1516B tuner amplifier. Manufactured by Marconi in 1944, it's pictured here on the left completely as received and, remarkably, still giving a good account of itself. This wonderful old receiver was offered to my collection by John Felten (PA5JF/ON5JF). John also shares a fondness for these old boatanchors and is currently concentrating his collection on equipment used by the Dutch Navy.

The B21 formed the basis of the FH3 high frequency direction finders used by the Royal Navy during WW2 to locate German U-boats. The FH3 was a primitive device that relied on the operator to determine the bearing of a transmission audibly. Interestingly, not only were they fitted to allied escort vessels but they were often seen fitted to the "tail-end-charlie" rescue ships assigned to the larger convoys as they were idealy placed to intercept radio transmissions from shadowing U-boats.

High frequency direction finding is thought by many experts to have been as much a war winner as Radar, Asdic and the breaking of the German ENIGMA code. In October 1941, the FH3 was first fitted to an ex-US Coast Guard cutter transferred to the Royal Navy and renamed the sloop Culver. Three months later, she was sunk by U-105 while escorting the West African convoy, SL98. This was a poor start for ship borne direction finders but thing's were soon to improve dramatically.

In order to counteract being detected, U-boats began sending convoy sighting reports in the form of bursts of high speed Morse code (Kurier system) which lasted typically less than half a second. Acting on information given to them by the British, French engineers working for a subsidiary of ITT in Paris, perfected a direction finder similar to the FH3 but utilizing a CRT display to obtain a fix on very brief radio transmissions. When Paris fell in the spring of 1940, ITT employees destroyed all the equipment and three of the engineers fled to America taking all the blueprints with them.

The Royal Navy Signal School, in close collaboration with Plessey, developed the FH4 which also utilized a cathode ray tube to display instantaneous bearings. This equipment is thought to have been based on Sir Watson-Watt's thunderstorm-location system designed in 1920. In July 1942, three examples of the FH4 were given to the US Naval Research Labs and American built versions were fitted aboard US vessels within 3 months. Allied escort vessels could now steam up the bearing of a U-boats radio transmission with their Type 271 centimetric-wavelength radars on line and force them to submerge allowing the convoy to escape.

Here we can see a close up of the turret assembly. Turrets were generally used to simplify the complicated switching arrangements needed on receivers with several RF stages and/or multiple bands. As is common with all early turreted receivers, large band change handles were used in order to generate the considerable force needed to actually rotate the turret. The R206 and B40 series receivers are two good examples of this. The chassis has to be very rigid in order to alleviate any twisting etc that would otherwise result in poor or intermittent contacts and this mechanical requirement is the main reason why the receiver weighs so much.

This image shows the unmistakably Marconi style tuning dial that they incorporated on many of their marine receivers up to the mid 50's. This design utilized a simple cardboard tube onto which calibrated scales were drawn along it's length. When a different band was selected on the front panel, the tube was rotated to a new position using a small chain to reveal the appropriate scale. A wire cursor traveled parallel to the tube by means of a small belt and a series of pulleys and displayed the approximate frequency the receiver was tuned to.

Unlike the famous 'CR' series, no vernier logging scale was provided for and finding your way about on the bands must have been very difficult for the operators. I wonder what they would have made of my Ra1792 which can tune down to 1Hz? - probably complain that they couldn't use it in the dark .

Besides the shear size and weight of this beauty, the first thing that struck me was the widespread use of engraved labels on the front panel. Etching or engraving a large steel panel was an expensive operation and was only commonly carried out on large production batches in order to reduce the manufacturing costs involved. From a restorers point of view, the multitude of labels on this panel will make a fresh paint job a very easy exercise.

These are the "Sense" aerial and goniometer "Search coil" connections mounted on the left hand side of the receiver. A "Search" aerial for normal listening was connected to the block on the top left of the front panel.

This is the power supply which has been built into the rear of the cabinet. Originally the receiver just had a transformer to supply the AC heater voltages but this has been neatly modified at some stage to provide the HT voltage as well. Due to the nature of use of this receiver, all wiring carrying AC PSU voltages use screened cables. I plan leaving the PSU modifications as-is after first tidying up things and performing some safety checks.

Although the paint finish on the front panel was looking a bit tired, it was in fact damage free. This image shows the receiver cleaned with a light cutting compound to remove the years of grime and restore the colour back to original. The big Muirhead dial and handles etc have been treated to a new coat of black enamel paint and the chrome items polished.

American metal envelope valves have been fitted to this receiver sometime in the past and the original screening cans discarded. I plan returning things back to original and have ordered a set of glass valves from my friends at Crowthorne Tubes and set aside some authentic screening cans. The receiver has also been recapped with modern components but I am hoping to obtain some original "stud mounted" capacitors and fit new 0.1uF, 400v components inside them. These will also provide the proper anchor points for much of the wiring and should improve the cosmetics below chassis.

Although I have the full circuit diagram for this receiver, I'm missing some of the component values, particularly those for R38 and C68 upwards. This is going to delay things for me as the second detector stage has been modified in the past to use the more readily available EBC33 instead of the original DH63. If there are any "long armed brothers" out there that can help here or, can tell me a little more about the B21's history, I would really appreciate it.

I decided to purchase this receiver without hesitation because of the history attached to them and their rarity. I had previously seen a photo of the front panel but not an internal image so I half expected it to be full of Belgium spiders and show signs of 60 years of decay.  In fact my first planned job was to dig the garden hose out of the shed and spend the rest of the weekend just cleaning things .  I needn't have worried as it turned out to be a very good example and needed little work to bring it up to scratch. I can't express enough how pleased I am in getting this receiver and would like to thank John for offering it to my collection and going through all the trouble to return this beauty back to Blighty where it belongs.