Beam tetrode

A Strahlpentode or beam power tetrode is an electron tube with special sheets to the concentration of the electron current from the cathode to the anode. She appears all too frequently in guitar amplifiers and high fidelity amplifiers of high-end class.

History

Engineers of the Dutch electron tube manufacturer Philips had switched to the suppression of secondary electrons, an additional grid ( suppressor grid ) between the anode and the screen grid tetrode one. Since Philips had a patent on this pentode tested other manufacturers to find other solutions to avoid royalties. The engineers Sidney Rodda and Cabot Bull by EMI in the UK developed the beam -power tetrode and received it in 1932 for a patent. Since the production was considered difficult, the principle came to the American RCA, which then developed several successful beam -power tetrode.

Operation

In the beam -power tetrode the pentodentypische suppressor grid is replaced by specially shaped Elektronenleitbleche that focus the electrons flow from the cathode to the anode and through a space charge effect a similar effect on unwanted emission of secondary electrons from the anode unfold like the usual suppressor grid of a pentode. While this tube also has five electrodes in the electrode system, the function of which also corresponds in principle in a pentode to bypass the Pentodenpatents but it was referred to as ( Beam Power ) tetrode.

Application

The best known representative of a Strahlpentode is the 6L6, which was first brought in 1936 as a steel tube with octal by RCA on the market, but was later produced as Allglasröhre in the glass flask. The performance of the 6L6 was oversized for applications in home radios, therefore, brought the end of 1937 the RCA optimized for such applications 6V6 out. With a single power tube amplifier of this type could be produced in the A- operation with about 5 watts output power. Other well-known representative of this tube type are the KT66 and 1956 by General Electric Company ( GEC ) KT88 introduced, which is often used in high-fidelity amplifiers of the high-end class.

In guitar tube amps today as power tubes mostly, besides the EL84 pentode (eg Vox ) or EL34 (eg Marshall), the Strahlpentoden 6L6 or 6V6 (eg Fender ) is used.