This allowed the balance control to be made the same size as the other major knobs and simplified operation. The complicated filter dial and variable slope selector were replaced with a simple top-cut switch. ![]() The controls also better matched a typical user's needs. Rated at just a quarter of this, the Stereo 30 Plus hardly stressed them at all, pointing towards durability. Capable of dissipating up to 115W of heat, these transistors allowed reliable amplifiers of up to around 60W output to be constructed. Meanwhile, the output transistors used were the classic RCA 2N3055, the basis for many classic transistor amps of the period such as the Quad 303, B&O Beolab 5000 and Braun Regie 510. This change certainly makes servicing beautifully straightforward. ![]() The slots were home to four small PCBs, one preamp module and one power amplifier module per channel. This was replaced with a hand-wired aluminium chassis onto which four edge-connector slots were mounted, the metalwork also forming the heatsink for the output transistors. The original amp had been built on a single PCB that carried almost the entire circuit. The Stereo 30 Plus was essentially the original concept built around a complete lineup of silicon devices. Quieter and more stable, silicon made it possible to build high-gain, high-power circuits with relative ease. Nevertheless, the Stereo 30 was well regarded and sold successfully until the appearance of silicon transistors in the middle of the decade signalled a step change in amplifier performance. They worked but were noisy and prone to thermal runaway, making it a challenge to design practical hi-fi amplifier circuits using them. The Stereo 30 used germanium transistors because that was all that was available at the time. Two lots of 15W easily trumped the outgoing Stereo 20 valve model, even before the improvements in reliability and performance due to the elimination of the output transformer (both key claims by Leak at the time) were taken into account. The number '30' equated to the sum of the outputs of both channels when measured under the most favourable conditions. The Stereo 30 was Leak's first transistor amplifier. Side by side the two looked much the same, but inside the 30 Plus was all new in order to take advantage of improved technology. This was certainly not the case with the Leak Stereo 30 Plus amplifier of 1969, which replaced the Stereo 30 first seen in 1963. Often the changes are minimal: a tidied-up fascia to match a new model added elsewhere in the range, or an extra function or minor circuit redesign. ![]() It's not unusual for a successful hi-fi product to be updated with mild revisions during its lifetime. While a near dead-ringer for the amp it replaced, this '60s integrated saw Leak leverage new technology to boost performance and widen its appeal.
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