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Vintage Radio Three “kindred” radios from STC By Assoc. Prof. Graham Parslow The BGE Dapper (green), STC Pixie (grey) and STC Bantam (red). The sales motto for STC was “for tone it stands alone”. The STC parent company in the UK was the primary supplier of English telephone systems, and STC was the first to use fibre optic cable for telephone transmission. STC also partnered with several US companies under the ITT umbrella to share technology. STC merged with BGE in the UK after World War 2. STC eventually failed globally in 1991 due to losses from computer manufacturing. The history of BGE Standard Telephones and Cables’ name was chosen to imply that STC was the standard by which others would be judged. That is probably a bit of a stretch, but you can at least say that the three Australian-made radios covered in this article from the mid-1950s have striking appearances that are definitely of their era. S TC started out in London as International Western Electric in 1883. It became STC in 1925 when it was taken over by ITT (International Telephone & Telegraph) of the USA. STC’s high points were supplying the entire radio systems for the liners Queen Mary and Queen Elizabeth (1936-39) and patenting pulse code modulation (1938). 90 Silicon Chip Their Australian operations date from 1923, when Western Electric set up a subsidiary in Sydney. Local manufacturing expanded significantly in 1936 with a new factory in Botany Road, Sydney, employing 700 people. Domestic radios were a minor part of STC operations, with commercial transmitters and military equipment being their major activities. Australia's electronics magazine BGE is British General Electric, a name created for Australian operations. The General Electric Company (GEC) rose to be a major UK-based industrial conglomerate producing consumer and defence products. From a small retail company in 1886, the company prospered through two world wars and amalgamation with Marconi. GEC merged with English Electric in 1968, a company famous for making jet aircraft like the Canberra and Lightning. GEC operations were broken into subsidiary companies after 2001. In 1999, GEC was renamed Marconi. That same year, Marconi Electronic Systems was sold to British Aerospace to become BAE Systems. Telecommunications giant Ericsson acquired the bulk of the remainder of the company in 2005. HRSA member Peter Hughes posted the following information about Australian operations at siliconchip.au/ link/abhi The British General Electric Co. started importing British-made sets into Australia under the name Gecophone from 1924 (a portmanteau of GEC-o-phone). The Gecophone radios sent to Australia were manufactured at the Coventry works (UK), which was “equipped with the most up to date machinery in the world”. Australian siliconchip.com.au A close-up of the dial used in the 1933 Genalex Dapper-5. The chassis of the STC model A5140 ► Bantam radio with the valves marked. models were “minutely adapted to suit Australian regulations and conditions”. A complete Gecophone two-valve radio with headphones cost £35 in 1924. Evan Murfett has described and illustrated many of the beautifully-­ presented Gecophone receivers of 1922-25 in the HRSA magazine “Radio Waves”, in a five-part series commencing in issue 146, September 2018. In 1929, the Australian government imposed a high tariff on imported radios. After 1930, BGE sets were manufactured in Sydney by Thom and Smith Ltd (Tasma) under the name of Genalex. The dial of a 1933 Genalex Dapper-5 from the author’s collection is pictured above. Also in 1933, the company made an agreement with Amalgamated Wireless Valve Co. Ltd. (AWV) for valves to be made with the Osram brand. The Osram boxes were marked “Made in Australia for the British General Electric Co. Ltd.”. The brand used for radios was changed from Genalex to BGE in 1953. Between 1956 and 1962, BGE-branded products were manufactured by STC in Australia, reflecting the amalgamation of STC and BGE in the UK. At no time was GEC (UK) affiliated with the General Electric Company of America. General Electric (US) had an association with AWA in Australia, marketing badge-engineered AGE radios that were clones of AWA radios. by using contemporary dual-colour plastic cases with the speaker grille moulded into the face. However, they are much the same internally, with the Dapper and Bantam being identical. The case design of the BGE Dapper is from the UK, while the Pixie is a reproduction of an ITT design from the USA. The Bantam & Dapper circuit An identical STC model 5140 chassis is used for both the Bantam and the Dapper radios. The original circuit is shown in Fig.1. Although ferrite antennas were becoming common in the mid-1950s, these radios have a conventional aerial coil with standard circuitry around the 12AH8 mixer valve. The local oscillator is the Armstrong type with a discrete coil to generate positive feedback to sustain oscillation (the 12AH8 triode oscillator couples internally to the heptode grid number three). The 9-pin 12AH8 valve is a rarity in Australian sets. It was designed by STC in the UK and released in 1953 under the brand Brimar, an STC An advert from 1955 showing off the STC Bantam model A5140. It has a plastic case and was sold with more colour options that those listed in the advertisement. The three featured radios The green BGE Dapper, the grey STC Pixie and the red STC Bantam were all current in the mid-1950s. Stylistically, they appear to be linked only siliconchip.com.au Australia's electronics magazine March 2023  91 Fig.1: the circuit diagram for the STC model 5140 radio. Note that while the circuit has been relabelled, there might be mistakes in the values due to the poor legibility of the original diagram. Power switch S1 is ganged to potentiometer P2 and is shown in the off position. C4 & C6 are ganged (15-450pF). C9, C10, C12 & C13 are all 75pF. subsidiary. The 12 prefix indicated that the heater requires a 12V supply, but this is a centre-tapped filament to allow two 6.3V connections to heat the cathode. The 12AH8 found application in UK and US sets with no mains transformer, using a valve series with heater voltages that add up to the mains voltage. In this radio, the 12AH8 recommends itself for the high stability of the local oscillator and high sensitivity provided. The STC service notes for this Bantam claim that only 10µV of signal is required for adequate reception. The intermediate frequency signal at 455kHz is passed to a 6BA6 valve for amplification. The 6BA6 was released by RCA in 1946 and became a popular RF amplifier globally. STC manufactured the 6BA6 under the Brimar brand. The resulting amplified IF signal passes to a 6AT6 double diode-­triode, also released by RCA in 1946 and commonly partnered with a 6BA6 IF amplifier. The volume control (500kW) is designated P1 and determines the audio level fed to the 6AT6 audio preamplifier grid. The ground return is via R14 (200W), which in theory should not prevent the volume control from achieving null volume. Still, in practice, most of these radios have some small residual audio output with the control at minimum. The junction of R13 and R14 provides negative audio feedback from the speaker to minimise distortion and improve frequency response. The sound is rather strident unless the topcut tone control (P2) is used to dampen higher frequencies. The 6CH6 output pentode operates with an anode voltage of 235V, allowing it to deliver 6W or more audio output. This valve is an STC UK design released in 1952 under the Brimar brand and intended for video amplification rather than audio. However, at higher volume levels, these radios rapidly enter into distortion because the Rola 5C speaker cannot handle much more than 2W (2.5W in the specifications). Another limitation to output power is the small Rola 5kW:3.5W output transformer that just fits in the limited space above the speaker. It is unfortunately common for these An aluminium dial version of the STC Bantam radio. The chassis underside of the STC model 5140 (Bantam series). 92 Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.2: the circuit diagram for the STC model 5162 (used in the STC Pixie) which is mostly identical in design to the model 5140 apart from some component changes. small transformers to have open primaries. Replacing them with a larger standard transformer (which is generally the only realistic option) requires some creativity in the mounting. The dial stringing diagram for the Bantam and Dapper reflects a simple solution to driving a dial at the left-hand side by a knob at the righthand side. A long shaft across the top avoids complex runs of string threaded around guide pulleys. An unsophisticated timber bobbin redirects the string movement through 90°. The Pixie circuit The Pixie uses an STC model 5162 chassis. Although the case design makes this radio stand out, it is otherwise a conventional radio using readily-­available components. At a glance, the STC 5140 and 5162 circuits (see Fig.2) are similar. The first difference to observe is the use of a 6BE6 mixer in the 5162 (released by RCA in 1946), a valve choice that is common to many Australian radios. This valve also achieves a sensitivity of 10μV for effective reception. The 6BE6 sustains local oscillation The chassis underside of the STC ► Pixie. Compared to the STC Bantam, it’s a lot more spacious. siliconchip.com.au Australia's electronics magazine using a Hartley circuit (compared to the Armstrong circuit in the Bantam). The volume control is 1MW rather than 500kW in the Bantam. Other visible differences are mainly due to drafting choices in the circuit diagram rather than circuit differences. The Bantam-Dapper chassis Thermoplastics allowed any concept to become a reality, cheaply and in great quantity. The fifties was a time when plastic was fantastic and atomic energy was about to transform Shown from left-to-right, top-to-bottom are the Bantam series of STC radios from 1946, 1948, 1950 & 1952. Despite being part of the same series, the chassis varied wildly between them. Right: an example of a STC Dapper sporting a red case rather than the green shown in the lead image. Below: the rear interior view of the STC Pixie (also known as the STC model 5162). A clock version of this radio was also available (called the STC Radiotym). the planet. It was the period that gave us extravagant Cadillacs and radios in every colour of the rainbow. In one respect, it was a time like any other, in which stylists trumped the practical requirements of engineers. The mid-1950s STC Bantam was created on the stylist’s drawing board. After that, the engineers needed to make compromises to bring the concept to reality. The large capacitors of the day made for a cluttered layout that is difficult to troubleshoot. The hottest spot in the radio is above the 6CH6 output valve, followed closely by the 6X4 rectifier, and this commonly cooked the plastic above the valves. The hot spots are exacerbated by the closed design of the back panel. In later production, an aluminium sheet was fitted internally as a heat shield across the top, which did a reasonable job of protecting the plastic case. The Pixie is easier to work on, but it is still cluttered. The Bantam family of five After the second world war, STC catered to the market for a second radio in the home, and the first Bantam was a four-valve radio for the entrylevel market. The picture of the first four Bantams shows how style and taste changed in a decade. The 1950 model (called the ‘caravan’) and the 1952 model (called the ‘Eiffel Tower’ or ‘waterfall’) are particularly valued by collectors. A bit of nostalgia Every radio can be a TARDIS (for those Doctor Who fans) that transports us to another time and place. A red STC Bantam from 1957 transports me to my favourite aunt’s kitchen, where the Bantam radio resided on top of the fridge. That small modern kitchen was my aunt’s pride and joy because it was part of a bright new cream brick house. My uncle was a kind but stern man who exercised his right as head of the family to demand complete silence as he listened to Dossier on Demetrius and other favourites on the radio. This was Adelaide before television, when the radio was the entertainment and information hub of the house. I grew up in country SA, and it was exciting to go to the city and see that red STC Bantam on the fridge. SC 94 Silicon Chip siliconchip.com.au