LEAK TL/10 AMPLIFIER
Well, what a pleasure to be able to offer this exquisite TL10 which has been carefully stored since 1979. This device is quite special, the little brother to the TL12 and to many it sounds nearly as good at a much lower price. This one is a peach, just look at the cosmetics, some patina that would respond to cleaning but it's lovely. Then there's the valve line up:- Mullard EF86 yellow label, Brimar 6SN7GT, Marconiphone EL33 and a Brimar 5Z4G. As you can see, no bodgewit has been jazzing up the inside with modern components so it's waiting for sensitive restoration either by component replacement/restuffing or carefull re-comissioning with judicious reforming of capacitors.
Whatever, it's a scarce opportunity as there are not too many of these left and this one has the added cachet of a whole wodge of original correspondance with the factory and the owners own hand written notes on connections - simply super - provenence of this order is most welcome yet seldom seen. We have not powered this amplifier due to age but it is offered as a very good original specimen with good transformers for a collector to have, display rebuild and use as is desired. I shall leave you with a raft of photographs and a little more on the development and circuit topology of this venerable and much feted amplifier: -
Following on from the 1949 introduction of the TL/12 to amazed Americans at the Audio Engineering Society exhibition in New York, the TL/10 was introduced as a lower cost alternative to the famous TL/12, but maintained the distortion rating of 0.1% but at a slightly reduced 10W output. Not so unexpected as the same circuit topology was used as in the big brother amplifier.
The circuit topology comprises a first stage of voltage gain, a triode long-tailed pair phase-splitter/unity gain stage, followed by a push-pull output stage (tetrode-ultra-linear) having either a common or individual cathode bias resistors (dependent upon circuit revision).
The TL/10 was the first Leak amplifier to incorporate the "ultra-linear" output stage configuration popularised by Hafler and Keros during the early 1950's but earlier postulated by the father of stereo, Alan Blumlein, in the 1940s during his time at Decca.
In 1952 H. J. Leak & Company published "a 28-page paper detailing the history, concept, and design of the TL/12 amplifier and the partnering RC/PA/U pre-amplifier. This pamphlet makes for fascinating reading for anyone interested in the history of the valve amplifier development during the "golden age" of thermionic high fidelity.
The valve line up of the TL/10 comprises of EF86, 6SN7GT, KT61 (x2 in Push-Pull) and 5Z4G. The KT61 valve has a very high mutual conductance with the Mullard EL33, the Mazda 6P25 and the 6AG6G being equivalent. Leak stated that 6L6 valves may be used in place of the KT61 but significant circuit modifications were required to do so.
Specifications: "Point One" TL/10 Power Amplifier
First released: 1950.
Total harmonic distortion: <= 0.1 per cent @10W.
Valve line up: EF86, 6SN7, 2 x KT61 in ultra-linear, 5Z4G
Steel chassis finished in gold enamel finish. Mono only.
Original UK purchase price: "Point One" TL/10 power amplifier for 17 guineas. A month’s average wage at the time!
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