Which tubes are suitable as high-quality replacement tubes for vintage audio classics?

For vintage audio classics, suitable replacement tubes in good quality are especially important. This applies to brands such as The Fisher, EICO, Harman Kardon, Klein + Hummel / Telewatt and Pioneer, as well as classics like Scott, Sherwood, Sansui, Dynaco or Leak. Typical audio tubes such as 7591, 7868, 6973 and ECL82 are often in demand. To keep these amplifiers, receivers or power amps reliable, carefully tested tubes should be used to preserve operating safety, sound quality and the classic character.