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The modern transistor radio has it's roots in the immediate post-war years. People in general longed to throw off the misery of rationing, and to leave behind the dark days of war. The 1950s saw an unprecedented increase in disposable income which in turn led to an increased desire for touring and holidays away from home. As a little boy during the '50s and a teenager through the Fab Sixties I remember coach (or should that be charabanc?) trips to the beach, and more and more families were able to buy and run cars. For me "The Sign of the Swinging Cymbals", the famous theme tune of "Fluff" Freeman's Pick of the Pops, still evokes nostalgic memories of trips to Wales on sunny summer afternoons - something we don't see so many of nowadays. Meanwhile Billy Butlin had established his peculiarly British holiday camps: the forerunner of today's package holidays - all-in holidays that had something for everyone even if the atrocious British weather did it's worst. Naturally, many wanted to listen to their favourite programmes while out and about, and radio manufacturers were quick to respond to the demand for reasonably sized and affordable portable radios.
While portable radios had been available pre-war, they were huge with an appetite for batteries to match. At the time a standard domestic radio carried a price tag equivalent to that of a top of the range colour TV today. Only well-off families could afford a similarly priced portable set, and the motor car needed to carry it around. However towards the end of W.W.II the need for small, light field comms led to American radio manufacturers developing a miniature, all glass 7 pin valve. Unlike their predecessors, these new valves had 1.5v filaments designed for use with single dry cells rather than accumulators, and decent gain at low anode currents, allowing the use of smaller, lighter HT batteries. The mini valve allowed the manufacture of truly small portables. The "attaché case" format was popular in the UK, while the States tended to follow a "miniature table radio" style or what I call "biscuit-tin radios".
RCA-Victor biscuit-tin valve portable
These new portables still suffered from one major drawback - the cost of running them. The batteries had an average life of sixteen hours, and a typical high-tension battery, the 90v Ever Ready B126, would set you back 35/-, or about £30 in today's money!! No wonder portables only came out for high days and holidays! To help maximise battery life, new ultra low consumption valves (the DK96, DF96, DAF96 and DL96 range) were developed with the filament current a miniscule 25mA coupled with a lower anode current requirement, and most manufacturers introduced mains/battery models for use where mains power was available. Meanwhile, December 1947 saw Bell Laboratories physicists Walter Brattain, John Bardeen and William Shockley make the most important discovery since the thermionic valve. A discovery that was to turn the electronics industry on it's head: the transfer resistor, a somewhat cumbersome name quickly contracted to "transistor". This device comprised two fine "cat's whiskers" with their points, spaced about 0.005" apart, pressed onto a slab of germanium, an arrangement graphically illustrated by the circuit symbol for a transistor. The first commercial examples of the "point contact" transistor, the Raytheon CK703, were introduced in 1948. Meanwhile Willam Shockley developed the junction transistor in 1949, with quantity production of junction devices starting in 1952.
I remember seeing the first adverts for transistor radios while a very little boy in the mid-'50s. The radio was described as using the "new cold valve" and could run for months on a set of cheap torch batteries. However transistor radios had one very great disadvantage at the time: their price. The cost of the transistors themselves was stratospheric, and the initial purchase price of a new transistor set was very high in real terms. To those used to scattering transistors like confetti throughout a design, the idea that a single device could cost the greater part of the average weekly wage may come as a bit of a surprise. Germanium itself is a scarce element initially extracted from the soot of smelting works chimneys. The chemical processes for refining germanium to the necessary purity added considerable cost, and the first transistors were hand assembled on valve production lines. While very early radios used torch batteries it wasn't long before the dedicated PPx "Power Pack" batteries were introduced with their press stud connectors of the same style as those on American high tension radio batteries. The most popular type was the large PP9 9v unit but a variety of shapes, sizes and voltages were developed. In fact all are available today except for the PP4: a 9v battery roughly the size of a "D" cell with a connector at each end. The transistor revolutionised home construction. Gone was the need for metal chassis and bulky HT batteries or mains power packs. Miniature radios could be built in plastic pill-boxes and operated by a small battery for months. One particular design by a certain Clive Sinclair appeared during 1958 in Practical Wireless, was eventually developed commercially into his Slimline kit model going on sale in 1963, with the famous Micro-6 and Micromatic following.
The very high cost of transistors spawned a variety of novel circuits designed to extract the maximum advantage from each expensive device. As far as radio projects went, this saw a return of the reflex circuit. Originally developed early in the 20th century when valves were scarce and expensive, the reflex circuit first amplifies the incoming signal at RF, detects it, then uses the same device to amplify the signal again at AF. Although a reflexed stage cannot theoretically develop the same gain as two separate cascaded stages, in practice the reflex gives very good results although tricky to design. Sir Douglas Hall was renowned for his amazingly way-out "Spontaflex" and similar designs, published in the now defunct "Radio Constructor" during the Sixties and early Seventies. Initially designs were restricted to long and medium wave coverage due to the limited frequency response of earlier devices, especially the cheaper surplus "Red Spot" audio frequency, and "White Spot" RF transistors, so named because of the colour of the paint spot identifying the collector lead - and if you you'd like some to play with, look here. Even the redoubtable OC44 mixer/oscillator transistor had an Ft of only 8 MHz. Short wave projects didn't become really feasible until the high gain 100 MHz Mullard alloy drift transistors (the AF11x range and OC169/170) became available at hobbyist friendly prices. Some sample prices taken from Mullard boxed devices in my collection are as follows:
Type Intended use Price OA90 Germanium signal (detector) diode 3/- (15p) OC44 Mixer/oscillator for medium- and long wave 8/3 (42p) OC45 IF amplifier 8/- (40p) OC71 AF amplifier in radios and deaf-aids 6/6 (33p) AF114 Alloy-drift RF amplifier to VHF 7/- (35p) AF115 Alloy-drift mixer/oscillator for long-, medium and short waves 7/- (35p) AF117 Alloy-drift RF/IF amp for AM and FM receivers 9/6 (48p) AC128 AF amplifier/output 6/- (30p) All plus Purchase Tax of course! These are mid- to late Sixties prices; bear in mind the take home pay for the average teenager like myself was around £6, fish-and-chips cost about 2/- (10p), a pint of best bitter 3/- (15p), and the weekly grocery bill for an average family was less than £5.
Radio was fun in those days. Like most kids I didn't go a bundle on school - although like most adults I'd give anything to relive those times. Weeks were a drab procession of schooldays punctuated by the jewels of Saturday and Sunday. From my early teens, after homework had been disposed of, then was the time for messing around with bits of old radios and TVs. It's often stated that everyone around at the time knows exactly what they were doing when President Kennedy was assassinated (November 23rd 1963): I heard about it on a little amplified crystal set built on a piece of card cut from a Corn Flakes packet. I lived in Heswall on the Wirral at the time, and the only station my little wonder would pick up was the BBC Third Programme on medium wave broadcast from a local relay transmitter about eight miles away on Rock Ferry pier in Birkenhead. For Christmas that year my parents bought me a Tri-onic electronic construction outfit. This was the first and probably one of the easiest kits to use as, unlike the later Radionic and Philips Electronic Engineer play sets, Tri-onic projects were built by plugging plastic modules containing the components into printed circuit boards. Only the later Japanese Denshi-Block kits came close for ease of use.
Eventually I was banished to the sandstone outhouse in the garden. My parents wouldn't let me have mains power so I had to be satisfied with 24v AC supplied down bell wire from a transformer in my bedroom. Fortunately they weren't aware that transformers work both ways, and I soon arranged for a range of suitably interesting voltages to be available. One favourite experiment (euphemism for big flashes. loud bangs and, if I was very lucky, loads of smoke) was a very large capacitor bank made up of smoothing blocks from defunct tellies. If I remember correctly the total was about 4,000uF in all charged from one of my step-up transformers via one of those big, grey finned selenium rectifiers to about 300v. When the charging switch was closed the rectifier rattled and my lights dimmed for a couple of seconds. The reason for all this? Well 4,000uF charged to 300v is a lot of energy. This was used in my high energy physics studies into the behaviour of small metal trinkets and coins when subjected to an as-nearly-instantaneous-as-makes-no-odds 600 Joule discharge. I was of course blissfully unaware that electrolytics could explode if abused in this manner; as it was the wire links between individual capacitors were forever fusing. Both the bell wire and the poor old transformer upstairs often ended up a bit hot and bothered after some of these sessions! Other projects involved the construction of high voltage power supplies of varying sophistication, beginning with vibrators and ignition coils and extending to (usually significantly overrun) line output transformers and valves - some of these probably breached strategic arms limitations treaties. I was (and still am) fascinated with things that glow, and much experimenting was done with all kinds of discharge lamps. In fact we may have built the first plasma globe after connecting the base of a large light bulb to the output of a particularly successful high voltage unit. Looking back I must admit that I'm surprised to still be here to tell the tale, and if I look carefully at my fingertips I'm sure I can still see the tiny pinhole scars from scores of RF arc burns. Something's definitely missing from today's Safety Gestapo approved solid state electronics!
That's all for now, but I will add more reminisces to this page when I can.
Also coming shortly are pictures of my collections of transistor radios, valve portables, electronics play sets and scientific kit.
