The eight 6L6 beam tetrodes used in the Nightingale ADM-32 are an unusual valve for a modern design. The principles behind them were developed during the mid-1930s by Marconi-Osram in the UK to circumvent patents on the pentode held by Philips. In the beam tetrode, the electron stream is shaped by 'beam plates' inside to eliminate the 'kink' introduced by conventional tetrodes when called upon to handle large signals. It was RCA's 6L6 tube which saw the technology first used in a practical design. In the UK this tube is better known as the KT66 - its British equivalent - KT standing for Kinkless Tetrode. This valve was used to good effect in the classic Quad II mono power amplifier and its bigger brother, the KT88, remains a popular alternative to the Philips-designed EL34 and EL37 pentodes of today.
展开▼
