I build most of my own gear because not only can I not afford gear costing 4, 5, or especially 6 figures, but for all the money you can't always pick and choose what you want. I see a $10,000 tube amp advertised on this site which has electrolytic capacitors, which go bad after a few years. For that kind of money I want polypropylene capacitors which have an indefinite life expectancy and ESR of at most a few hundredths of an Ohm. Where can you get an SET that has this but to build it yourself? There is a $350,000 SET that can be built for under $2000 in parts. I want the freedom to design the chassis in a style that looks like it is from a Jules Verne novel.
Several years ago I built my 833A SET which I drive with 245's which I like better than the 300B in the $350,000 stereo. I can choose cathode biasing resistors for the 245's that allow me to couple 6SN7's in choke loaded mu follower which is the best way to do it. I can get off the shelf output transformers that can carry 400 ma before core saturation with the 833A's only having to draw 120 ma at zero grid bias, something you can do with the 833A at 1000 plate Volts. Over the last 5 years I tried different ways of coupling the 245's to the 833A grids: parallel feed, capacitor, and upgraded to Lundahl 2765 which sounds best.
I upgraded parts in my components and rarely components themselves and once I have what I like I keep it indefinitely.