You are correct that it is relatively easy to build an SET amp. Plans and parts are readily available. The low parts count makes them fairly simple to construct and you will probably end up with a good sounding amp saving a lot of money in the process. Building a great sounding SET is a different matter.
Wavelength is also basically a DIY operation, it is just that the "yourself" in that operation, Gordon Rankin, has been doing it for many years. Since that is what he does, he has the chance to experiment with many different designs and parts. I would venture to guess that for every itteration that he puts on the market there are many, many more that he has rejected.
As for jobbing out a DIY, most kit companies offer their amps as assembled units. Exemplar Audio will assemble and/or modify a bottlehead SET amp for you. I think that kind of defeats the purpose of DIY but you will have a very nice sounding amp at a reasonable price. However, you can have a Wavelength Duetto on the used market for about what you would have in the bottlehead. At that point it is a matter of taste.
I agree with TWL that 8 watts should be plenty, which BTW is what a Wavelength Duetto and a host of other 300B SET amps produce.
Wavelength is also basically a DIY operation, it is just that the "yourself" in that operation, Gordon Rankin, has been doing it for many years. Since that is what he does, he has the chance to experiment with many different designs and parts. I would venture to guess that for every itteration that he puts on the market there are many, many more that he has rejected.
As for jobbing out a DIY, most kit companies offer their amps as assembled units. Exemplar Audio will assemble and/or modify a bottlehead SET amp for you. I think that kind of defeats the purpose of DIY but you will have a very nice sounding amp at a reasonable price. However, you can have a Wavelength Duetto on the used market for about what you would have in the bottlehead. At that point it is a matter of taste.
I agree with TWL that 8 watts should be plenty, which BTW is what a Wavelength Duetto and a host of other 300B SET amps produce.