Where can I find high-quality replacement tubes for DIY classics, for example from Elrad, Elektor, Heathkit, Bubeck or Raphael?

For many vintage DIY and self-build amplifiers, suitable replacement tubes in good quality are still in demand today. This applies, for example, to classic ELRAD projects, well-known Elektor concepts such as Williamson variants, the designs by Mr. Haas from Experience Electronics, Welter Electronics, later Raphael, Bubeck 300B projects, as well as Heathkit classics such as W-5M and AA-100. Typical tubes in this field include EL34 / E34L, KT88, 300B, ECC83 / 12AX7, ECC82 / 12AU7 and, depending on the circuit, also EF86 or 6550. These are available from BTB in premium matched quality.