The phrase refers to hoover tubes, particularly the HTA 100 mannequin, produced throughout their preliminary manufacturing interval. These tubes have been essential parts in early digital gadgets, significantly audio amplifiers, radios, and take a look at tools. Their building and traits outlined the efficiency capabilities of the tools by which they have been used.
These authentic tubes are vital as a result of their distinctive sonic qualities, construct high quality, and historic significance. They usually exhibit totally different efficiency traits in comparison with later manufacturing runs or reissues. The shortage and desirability of those tubes amongst classic audio lovers and collectors stem from their perceived superior sound and historic worth.