When talking about iconic tuners two or three words often come to mind; ‘Leak’ and ‘Trough-Line’. Only a few other tuners, the Quad FM3 and Marantz Model 2110 with built in oscilloscope get me excited.
The 1950’s marked an important change in listenership, as short, medium and long-wave broadcasting became unacceptable sound quality as our ears adjusted to the improving musicality acquired by high fidelity turntable, amplifier and loudspeaker separates beginning to appear on the market. Luckily the BBC with UK company STC (Standard Telephones and Cables) supplying the tuners worked together to research and trial the new Frequency Modulation FM technology, a system that gave far better noise level and increased frequency response (and later stereo). Harold Leak at his company H. J. Leak and Co. Ltd, based at 57-59 Brunel Road, Westway Factory Estate, London W3, had already gained a good reputation for his amplifiers, especially the “Point One” range; ‘point one’ relating to the then miniscule distortion level of 0.1%. He was able to get hold of an STC tuner so he could test out the technology, and even show off a tuner to the public alongside their own products. Thinking these weren’t good enough for their own high standards they began to develop a model for themselves in 1954, with Ted Ashley, Stan Amos and G.C. Johnson, the latter two who were both ex BBC engineers.
After a year the first tuner was produced. This was called the ‘Trough-Line’, the name derived from the tuning element being used. You see, a big problem in early tuners was that due to changes in temperature (valves heat up!) the components, notably the inductors inside the tuned circuit that are used to control the local oscillator and hence tune to the radio frequency you need to hear, would change dimensions and therefore vary the inductance. This meant that you would regularly need to retune the radio to keep the radio station playing at its best. The Trough-Line series worked, like most tuners do, on the superheterodyne principle where the radio frequency is mixed with the output of a local oscillator to produce the intermediate frequency (IF) signal. In the case of the Trough-Line it is 12.5MHz. That means that for say Radio 2 88.3MHz, the local oscillator is tuned at 100.8MHz. By mixing these together the difference frequency is 12.5MHz. For Classic FM at 100.4MHz the local oscillator will therefore be tuned to 112.9MHz. If the local oscillator is drifting about then it will be hard to keep “tuned in”. The answer was to make “U” shaped trough as the outer transmission line conductor, hence the word “Trough”, with the open end facing down. This was actually also a cheaper design option, but it worked brilliantly, keeping heat changes to a minimum. Also, unlike most tuners that used wound coils as inductors, the Leak tuner used a tapped transmission line, hence the word “Line”. From this the name “Trough-Line” was adopted. The later Mk 2 used a metal cylinder as the outer conductor, but kept the name, and much harder to get into if you needed to repair/adjust components.
The original Trough-Line was square shaped and very heavy (the trough itself had significant amounts of copper which also made it very expensive) and would tune from 88-100MHz, missing out most of the popular stations of today. The gold-enamelled steel unit with black writing had a very modern rectangular tuning dial with a volume and tune knob underneath, and the unit was also self-powered unlike most tuners of the period which had power fed from the preamplifier or amplifier. It had screw connections for the aerial at the back and an RCA output socket. This model was made until 1959.
The distinctive Mk2 Art-deco version appeared in 1960, with its gold-brown front panel made of Diakon (a type of acrylic plastic made by Lucite International Inc.) fitting in well with the Varislope preamplifier that itself mates with the Stereo 20 power-amp. This model extended the tuning range so it went from 88 to 108MHz. This also used a copper plated mild steel oscillator tube to keep down cost and weight. The original three engineers worked on the development of this model. FM Stereo decoding hadn’t yet been decided in the UK, so this model had provision for an external stereo decoder to be added if and when it was available, connecting to the RCA “Multiplex” socket at the rear. Interestingly, there wasn’t an RCA socket for audio-out, rather it had a basic lead with RCA plug exiting the rear of the unit. This model had switchable Automatic Frequency Control (AFC) and Local/Distance sensitivity control on the front panel.
The valve Trough-Line Mk3 was issued in 1964, which with its silver/black rectangular shape matched the transistor Stereo 30 integrated amplifier. This was the only change; the electronics being the same and still having the “multiplex” socket at the rear, but in 1966 when stereo was finally adopted in the UK (following the USA General Electric – Zenith system, first trialled as far back as November 1934 from the 85th floor of the Empire State Building!) a new model was produced called the “Trough-line Stereo”. This model also retained the screw connections for the aerial and now had two internally connected RCA leads, one for each channel. For a while an internal stereo upgrade was offered to owners of the mono Trough-Line 2 and 3 versions. Interestingly both the mono and stereo versions of the tuner were on sale together, at £32 and £47 respectively. Tests in stereo from the BBC from their Wrotham transmitter started as far back as 1958. Broadcasting in stereo didn’t appear until the 1970’s, but this was sporadic and only on Radio 3. Interestingly the link from Broadcasting House to the Wrotham transmitter went PCM digital from 1972 improving the S/N ratio significantly, making live Radio 3 stereo broadcasting even better and heralding the start of Radio 2 stereo.
When it was decided to change from valve to transistor in 1969 Leak brought out the Stereofetic, itself a good looking tuner, now with buttons, but somehow it has never had quite the same excellent sound quality and none of the historic importance that make any of the tuners sought after hi-fi antiques. Interestingly, whilst the name Trough-Line is important, the best of the tuners didn’t actually have a trough!
I have always considered Harold Leak one of the most important pioneers of hi-fi, better known for what he achieved in the early years rather than at the end. He was a popular man, often driving about in his Rolls Royce, and with his son, Simon, working with him from the 1960’s. The Point-One series and the TL tuners, and even the sandwich speakers (that’ll be for another Retro Byte) make him the sort of person I wish I had the fortune to have known in my life of hi-fi addiction. Maybe I will meet him in Hi-Fi Heaven. I don’t believe the Trough-Line has been bettered, and if you can pick one up it is worth servicing it and replacing some of the components, particularly aging capacitors and resistors. Then it will sound even better, as long as we continue transmitting on FM.