The Focus Transistor Set
The Focus leaflet - unlike that for the Studio ‘E’ series - never got lost! The images available on this page come, with the BBC's kind permission, from the copy that has been in the care of their Written Archive Centre for over 50 years. So, in contrast to Doug Brown's tattered copy of the earlier leaflet, the Focus leaflet shows its age merely by the yellowing of its paper. Until recently I have had to withold one of the four pages for rights reasons. This issue has now been resolved, and I am pleased to be able to include the entire leaflet in the download. I'm sure you'll enjoy the fourth page! We start with some points about the leaflet itself and the circuit design, then the image downloads. Finally, I include some recollections by correspondents who built the set all those years ago.
The leaflet is a single sheet, about 19.7 x 12.4 inches, folded to form a four-page leaflet about 9.8 x 12.4 inches. The front page carries the Written Archive Centre's handwritten unique identifier. It also carries the date 23 March 1959, when the series proper began following the appetiser programme on 9 March. The first three pages of the leaflet contain all the information for the transistor set (see below). Page 4 contains two advertisements - of great period appeal - for BBC publications.
The upper advertisement is for a 1959 booklet entitled Spotlight on BBC Television, which contained several cartoons by "Artie". Arthur (Artie) Jackson (c1910 - c1975) became well known for his topical cartoons for the Daily Express. The advert includes one of the cartoons from the booklet, Artie’s light-hearted take on the problem of poor reception due to reflected signals (ghosting). Entitled "Ghosts are often troublesome", it shows the man of the house entering the darkened tv room to discover two ghosts watching television!
When I first applied in late 2011 for permission to reproduce the leaflet, the BBC was happy to allow me to reproduce the three pages containing Davey's design details, but was uncertain of its re-use rights in this cartoon, and therefore could not allow me to reproduce the page containing the advert unless this concern could be resolved.
My initial efforts failed to make progress on this. In January 2014, a member of Arthur Jackson's family contacted me having visited this site, and put me in touch with his executor, Mr David Jackson, who has kindly given me permission to reproduce the cartoon. The BBC has, in turn, allowed me to reproduce the fourth page of the leaflet. I am most grateful to David Jackson and the BBC for enabling me to reproduce the leaflet in its entirety for you to enjoy.
The circuit and practical layout
As mentioned on THE BBC SETS > page, Gilbert Davey had relaxed his early reservations regarding transistors for the amateur constructor, and had published transistor radio designs in the January and October 1957 editions of Boy's Own Paper. The Focus design has some similarities to the second of these designs.
The Repanco DRR2 coil specified for the Focus set was designed for valve sets with reaction, and has long-wave, medium-wave (tapped) and reaction windings. For this design, the reaction winding is used as an aperiodic aerial winding. It was in plentiful supply then, but is hard to find now. The signal to the crystal diode detector is taken from the medium-wave tapping. A wavechange switch is shown as optional on the coil wiring diagram, but is not included in the components list. A short aerial wire was suggested.
Gilbert Davey would have been well aware that a simple crystal "front end" like this would have poor selectivity, especially as compared with the regenerative one-valver of the previous BBC series. Better results can be obtained with a crystal detector by using more sophisticated bandpass tuning arrangements, but these usually involve multiple coils and, ideally, ganged tuning capacitors. An alternative might have been a reflex design, but this is again more complex and requires a radio-frequency transistor - no doubt an expensive item in 1959.
Two stages of audio amplification follow the detector. As an indication of Davey's progress on the transistor learning curve since the October 1957 BOP design, the base biasing resistors are of higher values than in the earlier design, for longer battery life. However, both stages are in grounded-emitter configuration, without emitter resistors or bypass capacitors. According to my understanding, this arrangement means that stage gain is very dependent upon the variable properties of individual transistors (Hfe for OC71 quoted as 30 – 110).
Davey had included these emitter circuit components in the October 1957 BOP design mentioned above, and also in that in Chapter 14 of Fun with Radio, second edition, published in 1959 and thus roughly contemporary with the Focus series. So it is puzzling that he omitted them from the Focus receiver. When the series was aired, he might perhaps have told viewers how to retro-fit these components, but this could have spelled confusion for young constructors. (To compound the mystery, Davey again omitted these components from the transistor design published in BOP April 1961.)
We must conclude that it was decided to go for a simple design with moderate overall cost for first-time constructors. The appeal of the series would have lain in the novelty of transistors, and the small size and portability (compared with a valve set) that even an inexperienced constructor could achieve.
For headphones, the leaflet specifies "any type, or deaf-aid earpiece". This is a little vague, given that maximum collector current for an OC71 is 10mA, and the impedance of some hearing-aid earpieces is as low as 160 ohms. Perhaps during the programmes advice was given on choice of phones or earpiece.
The specified PP4 (or type 226) 9-volt zinc-carbon battery had a cylindrical body, 41.5mm long x 25.8mm diameter, with a snap connector at each end, giving total length 49.8mm. Its diameter would have set the minimum overall thickness of the finished set. The PP4 was quickly superseded by the ubiquitous PP3, and is now unobtainable on the High Street, but an alkaline version is available at http://www.smallbattery.company.org.uk for anyone rebuilding the set and wishing to use a battery similar to that specified.
Construction on the suggested 2 3/4 x 5 1/4 inch baseboard is as a simple hook-up, with the wiring all on one side. No mounting arrangement for the coil is shown; perhaps a simple bent bracket was described during the programmes.
As the stories below attest, the design's limited performance does not seem to have detracted from the enjoyment and sense of achievement of those who built it. Housed in a suitable case, with an aerial lead and projecting tuning knob and wavechange switch (if used), the set just about qualifies as pocket-size. But those who built it, then showed it off at school or summer camp when the transistor was still a novelty, would surely have found that it was an object of wonder and envy!
I have now built this little set, and you can see pictures and further comments about its construction and performance on the My Focus Set page.
These images are BBC copyright, and available for your personal non-commercial use only. Please also read the copyright notice on the WELCOME page. If you wish to pass them on to a friend, please send a link to this web page. He will then have access to the viewing and printing suggestions as below. The images are available below in two forms:
PDF file: (You need Acrobat Reader installed on your PC.) File size is now 2.2Mb (larger than formerly in order to do justice to the cartoon), and a broadband connection is recommended.
Click the icon to download the PDF file. If Acrobat Reader opens within your browser, use the "Back" button to return to this page when download is complete. If Acrobat Reader opens in a separate window, close that window to return to this page.
All four images are positioned within a PDF file so that when printed on one sheet of A3 paper, the pages appear in order (page 1 and 4 on one side; pages 2 and 3 on the other). The original leaflet is somewhat larger than A3, so the PDF file has been scaled down to fit within this size, yielding a leaflet around 80% (linear) of true size. Having printed the file on to A3 paper, you can then trim off the blank paper round the edge, leaving a sheet about 16" x 10". Fold this in half to form a four-page leaflet.
If A4 paper is the largest your printer can handle, it is probably easiest to use the individual JPEG images below.
JPEG page images: High-resolution files, each 2000 pixels by 1587. Exactly as supplied by the Written Archive Centre, unretouched, but with just a little compression for reduced file size without significant additional fringeing etc.
Click any of the thumbnails below for access to individual page image files (each 145 - 186kb). Each will be displayed on its own in your browser. Do not be disappointed by their initial appearance - your browser will downsample the displayed screen image to fit the window. Use your browser's "Back" button to return to this page.
Printing depends on the capabilities of your image software and your printer. Size each image so as to occupy the full width of a "portrait" A4 sheet, leaving an inch or so at top and bottom. You could tape together two A4 sheets (each printed both sides) to form a four-page leaflet.
Some recollections by correspondents who built the Focus set
I have heard from several correspondents who watched the Focus series, and indeed built the set. For them the series was as formative and memorable as the 1-valver series had been for me. So here are their recollections - stories that Gilbert Davey would surely have been delighted to hear.
I built the [Focus] transistor radio in 1959 - remember being ill in bed and being allowed up to watch one relevant session! I remember the leaflet - like a folded sheet of Radio Times - but alas it has long since disappeared. I remember being sold surplus transistors that generated an immense amount of noise, later replaced with Mullard OC71s, from memory at £1-10s-0d each, an immense amount at the time! All was constructed inside a cedar cigar box from a friend’s father who supplied all my “cabinets” for years! 73, Stephen Curtis, VK3CAX, but currently doing some work in Cheltenham!
It's a pity that not so many people smoke big cigars these days - at least as regards supply of "cabinets"!
Hi Les, just found your site while looking for info on my first transistor radio that I thought was featured on Blue Peter around 1958-ish. I remember writing in for a leaflet, and spending weeks of accrued pocket money on two transistors, "red spots" if I recall correctly. Anyway after looking at your site I guess it was probably the 1959 [Focus] design - Hmmm . . . This was just after my 14th birthday - and I used my pocket money and birthday money to buy the two "red spots". I can still remember the look on my mother's face when she saw what I had spent ALL my money on! Over the next year or so, I added an audio amp and speaker, and Dad built a box to house it all. It had a wire with a croc clip, and we'd go out on Sunday afternoon in our old van, stop somewhere with a wire fence, and hook it on! A couple of years later I applied to Southampton University for one of a handful of places in the new Electronics course. They had many applicants, all with top grades - so the tie-breaker was "Tell us what you have built". I know that this project, and the subsequent mods, were key to me getting accepted. That's how I got started down the career path that lasted 50 years, most at IBM, and ended with billion-transistor chips running a gigahertz! Without that I would probably have become the third generation in the family Fish Shop. Chris Parker.
That's quite a career path, Chris - "red spots" to gigahertz chips!
In advance of applying for full permission to publish the Focus leaflet, I was able (with the Written Archive Centre's permission) to pass on a PDF file to Stephen and Chris.
Hi Les, I was just browsing for any details of the BBC Focus 2-transistor radio which was promoted on BBC Children's tv around 1959, and came across your very interesting web site! I well recall constructing the radio at the time - I was about 12 or 13. I must have sent for the instructions by post, but can't recall where I bought the components. Maybe they were available as a kit, or I might have purchased them from a radio components shop in Norwich, my nearest source.
My father had taught me to solder and I remember wrapping the OC71/OC72 'top hat' transistors in a small piece of damp cloth to prevent heat damage whilst soldering their fairly long wires to the adjacent components. I think I built the radio in a clear plastic lunch-box - it was easy to drill to fix the tuner and there was plenty of room to work. I wish I could recall more details but it was a long time ago!!
The completed radio, which worked first time, had excellent sensitivity and plenty of volume compared to a crystal set I had previously. I enjoyed the radio for a while, until at school a boy with rich parents had a 6-transistor pocket radio in a leather case he flashed around. Incredible sensitivity and amazing volume from the tiny speaker! From then on that was what I wanted. He said it cost £14 (in 1960) which is about £275 in today's money based on the RPI - just think what kind of radio you could buy today for £275!
This was clearly well beyond my pocket money, but I thought I'd try and build one - quite a step up from the Focus! So I built a 6-transistor radio, presumably from a kit, but couldn't get it to work not having any test equipment. However my cousin was an RAF radar technician and soon got it sorted, and it gave good service for years. Happy days!! David, Norwich.
Tut, tut, those boys with rich parents – no tact!
A correspondent who prefers to remain anonymous writes:
I was about 14 when I built the Focus two transistor radio, and still have some of the parts and the instructions. I built it into a cigar box and threw the antenna wire out of my first floor bedroom window. As I was only four miles from the BBC Postwick MF transmitter I immediately dragged in a clear signal. I was elated, and asked myself the question: "How do the waves get out of the transmit antenna and into my receive antenna?". Fifty-five years later I am still asking the same question.
Later, working for the BBC, I was site engineer for rebuilding the MF antennas at Moorside Edge. Thirty years ago I joined a firm of consulting engineers to develop MF propagation modelling software.
Since retiring I have been assisting with MF antenna and propagation modelling and measurement for a Christian organisation that uses radio and other media to spread its message. I have recently taken delivery of an Excalibur Software Defined Radio, and am attempting to write control software to do MF monitoring and measurement.
It all started in 1959 with Gilbert Davey’s two transistor radio!
I'm sure that this splendid story would have made Gilbert Davey very proud indeed!
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|My thanks go to the BBC for their permission to reproduce the leaflet, to David Jackson for allowing me to reproduce the page with the "Ghosts" cartoon, to the BBC Written Archive Centre for supplying the images, and finally to those who have contributed their stories about this little radio set. If you built this set when the programmes were aired, or if you decide to build it now, please let me know!|