The Williamson amplifier is a design by the British engineer D. T. N. Williamson and was first published in the spring off 1947 in "Wireless World". Williamson was employed by "The M.O. Valve Company" (later with Ferranti ) as an engineer. The M.O. Valve Comp. was one of the constructors of the famous KT66 tube. The amplifier Williamson designed employed a pair of those tetrodes connected as triodes in a push-pull class A configuration and had a max. output power of aprox. 16 Watt. What made this design famous was its very low distortion. After war Europe had other things to do at that time and High Fidelity seemed a luxury. When the circuit design reached the mainland years later constructors reacted disappointed because the circuit was so simple. The high quality was the mere fruit of careful design and a very complicated output transformer. After a short period of popularity may constructors turned to the so called "Ultra-Linear" amplifiers which were invented a few years later. These gave more power with less tubes and seemed to have the same sound quality as the Williamson design at that time. We must consider that parts for tube amplifiers were very expensive at that time. A good outputtransformer for the Williamson Amplifier would cost a weeks wages or more and one must not be surprised that constructors would carefully compare every design in the financial aspect rather then looking at the last little bit of joy a triode class A amp. would bring.

Nowadays building tubeamps is a costly undertaking anyway and the reason people do this is merely because of the last little bit of joy that can be achieved when one looks carefully at every aspect of the amplifier, never mind the extra tube or that rare transformer. When one doesn't need an awful lot of output power the Williamson design is a construction one must consider since it is sounding very good and at the low levels of listening at home ( at night ) certainly better as comparable constructions of the Ultra Linear type. When one however wants to build a tubeamp. on a very tight budget one must be very patient and spend a year or so collecting the parts, when ones main diet is vinyl one can better start by building a good tubepre-amp. since that gives the greatest improvement for the money.

Is this amp still any good? Is it worth to build one? Are more recent circuits not much better? Williamson designed his amp for mono reproduction with a fairly high amount of negative feedback. That is ideal for mono. All designs in that time were mono-amps. Later, when stereo was invented, they just build two monoamps on the same chassis and claimed that it was a stereo amp. Unfortunately stereo amps must sound roomy and it is just not good enough to copy mono amps for stereo use. In most cases however decreasing the amount of feedback makes an amp better for stereo use. The Williamson design is still working perfectly with very little feedback because of its careful design. Later commercial designs are often developed for maximum power output with minimum parts. It is often claimed that the ultra lineaer circuit gives the powerstage the quality of a triode-connected powerstage without the disadvantages of the triodes. In fact this is not really the case. The internal resistance remains twice as high at the same level of negative feedback, the low power distortion is much higher but it saves one tube since it is easier to drive. The typical advantage of a triode-connected powerstage such as the Williamson is the low internal resistance that provides with low negative feedback enough damping for the loudspeakers. Striking results can be expected with speakers that require not that much damping from the amp. such as transmissionlines. Enclosures with the size of shoeboxes require in most cases a lot of damping from the amp. The result of high negative feedback levels can be described as the typical "Hear me sounding good and not forgetting any detail" sound of many amps that makes listening tiring.

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