Well, this is the amplifier I used to draw design diagrams for as a teenager in the mid-1970's, and then dream that I had built it! Unfortunately as the power goes up, the amplifiers become harder to find.
The TL/50 Plus amplifier is shown above is finished in the gold enamel of the earlier models. It is fitted with 6550 output valves, although originally they were mainly shipped with the fabulous Marconi-Osram KT88. Also, the unit above has a rather cheap version of the 5AR4 rectifier, which normally has a slightly bigger and less-rounded envelope. Originally Mullard 5AR4's would have been used.
Even though Leak produced a wide range of power amplifiers, all of them had the same high sensitivity, and the TL/50 Plus is no exception, with just 125mV giving 50 Watts out, with distortion reaching 0.1% at 45 Watts. In reality the amps would clip at just over 60 Watts. Feedback on the TL/50 was slightly lower than other Leak amps at 23dB.
Note that both the TL/25 Plus and the TL/50 Plus had a heat-shield to protect the mains transformer from the radiant heat from the output valves (although advertising shows that the earliset models made seemed to lack this feature). In the TL/50 Plus, a filter choke resides next to the power transformer (not visible due to the heat shield).
Around the time of the introduction of the Leak solid-state amplifiers (circa 1963), all the valve amplifiers changed from gold & brown livery to the grey & silver livery of the solid state amplifiers. A late model TL/50 plus is shown at the right. This unit is fitted with genuine MOV KT88's.
The Leak pre-amp plugs into the black octal socket on the left, and an input gain control and RCA connector are next to this octal socket.
The original photo of the grey TL/50 Plus was generously supplied by Andreas Ball of Germany.