Originally Posted by Uncle Erik
If you're going to spend $5k-$6k, get the best. Don't settle for 12AU7 and 12AX7 tubes. Those were originally engineered for inexpensive consumer products - not high-end audio. You want meaty triodes, at least octal tubes. And insist on point-to-point wiring. For that amount of money, don't settle for anything. $2k can get you top shelf parts for a custom 300B. The rest could be spent at a machine shop getting the exact case you want, a few sets of tubes and a happy, motivated builder.
Agreed. 12AU7s do NOT belong in audio amplifiers, their original application is in oscillators and handling sawtooth waves in TV and some industrial applications, they were never designed to be linear and they can't be made to work linearly unless it's as a CCS'd cathode follower. Even then there are far more linear tubes. 12AU7s belong in guitar amps, not hi-fi. The 12AX7 isn't as bad, but again, there are far better choices for hi-fi.
Personal thoughts. Run everything on directly heated triodes, Emission Labs makes a full line of them, use the 20A or 20B for input with the AD1, 2A3, or 300B on output duties. Use LC or transformer coupling along with a good set of output transformers. You can also substitute a 205D or WE437A as the input tube, these are very linear low distortion tubes which won't hold back the DHT output stage. Use the good stuff, it's within your budget.