The first consideration is the desired output power, as this determines everything that follows for the output and power transformers, and a great deal of the power supply requirements in general. Note that SET (single-ended triode) amplifiers and transformers will not be discussed, because as most readers of The Audio Pages will be aware, I consider them to be utterly pointless other than for playback of shellac (78 RPM) discs, where their high distortion and colouration will go unnoticed. Guitar amps pose some additional constraints, but these are easily accounted for (even though many guitar amp makers still haven't managed to get it right). This article looks at the requirements for both guitar and hi-fi amplifiers, and although the requirements for the output transformer are quite different, many of the issues faced are common to all valve power amps, regardless of how they will be used. Valve (tube) diodes have the inevitable nostalgia value, but they are fundamentally one of the most useless components you can include in a power supply. Chief amongst these is the choice of rectifier for the power supply. Obtaining the best performance involves very careful design of the transformers, and an idea that "seemed like a good idea at the time" can cause major problems in use. Valve amplifiers pose special challenges for the output transformer and power supply. For an even simpler overview, see Output Transformers and Power Supplies on the Lenard Audio website. The information is fairly technical, and without the general understanding of how transformers work, you will almost certainly have trouble here. If you are unfamiliar with transformers and the terminology used, Transformers - Part 1 and Transformers - Part 2 should be read first.
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