The phrase refers to hoover tubes, particularly the HTA 100 mannequin, produced throughout their preliminary manufacturing interval. These tubes had been essential elements in early digital units, significantly audio amplifiers, radios, and take a look at gear. Their development and traits outlined the efficiency capabilities of the gear wherein they had been used.
These authentic tubes are important resulting from 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.