Beam pentode

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Transmitter tubes 6146B, length approx. 97 mm, approx. 50 W HF power at 175 MHz
The inside of a jet pentode with a cut open anode plate. You can see the silver-colored baffles and in between the grids, which are clearly wound with the same incline.
UHF double beam tetrode QQE 06/40 with common screen grid and common cathode, height 105 mm, 90 W HF power at 200 MHz, 20 W at 500 MHz

A beam pentode , beam tetrode or beam power tetrode is an electron tube with special metal sheets to concentrate the electron flow from the cathode to the anode. It does not require a retarding grid like the classic pentode and still has its advantageous or even better properties.

It is used as a power tube from low frequency to UHF and as a control tube for high voltage. It occurs still common in guitar amplifiers and high fidelity amplifiers of the high-end of class.

history

Engineers at the Dutch electron tube manufacturer Philips had connected an additional grid ( braking grid ) between the anode and the screen grid of a tetrode to suppress secondary electrons . Since Philips had a patent on this pentode , other manufacturers looked for other solutions to avoid license fees. EMI engineers Sidney Rodda and Cabot Bull in Great Britain developed the beam power tetrode and were granted a patent for it in 1932. Since the production was considered difficult, the principle came to the American RCA , which then developed several successful beam power tetrodes. The first beam pentode was RCA's 6L6 , which was launched in 1936 and is still in production today.

Working method

The structure of a beam power tetrode is characterized by the following features:

  • The pentode-typical retardation grid is replaced by electron guide plates (beam plates), which concentrate the electron flow from the cathode to the anode in a narrow radial angle.
  • The control grid and screen grid are wound exactly one above the other with the same pitch, so that the electron stream reaches the anode in many narrow layers.

The concentrated negative space charge has a similar effect on the secondary electrons knocked out of the anode as with the retarding grid of a pentode: they are prevented from leaving the anode compartment and land on it again.

The beam power tetrode thus also has five electrodes , the function of which in principle also corresponds to that in a pentode, but the braking effect is primarily achieved by the space charge of the electron bundle and not by the beam plates. While conventional tetrodes have a region where the UI characteristic curve of the anode has a reversal point (risk of self-excitation, higher distortion factor ) due to the secondary electrons landing on the control grid, when the anode voltage is low , beam power tetrodes are more linear and have less feedback from the Anode on the control grid. The lack of characteristic kink (English kink ) earned them the designation kinkless tetrode and stood for the model number of early commercial tube of this type (KT66, KT88 etc.) Pate.

The equally long transit times of the electrons due to the narrowed path offer the further advantage of higher efficiency at high frequencies, since the electrons arrive in phase at the anode. Beam-power tetrodes can therefore also be used up to the UHF range.

Typical parameters

There are types with 1 kW continuous power at 1 GHz (or 100 kW pulse power with 1% duty cycle) or even with 1 MW pulse power (500 MHz) have been built.

The type 4X150A / 7034 delivers 390 watts of HF power at 500 MHz, has a maximum anode voltage of 2 kV and, including the integrated anode heat exchanger for forced air cooling, has a diameter of 42 mm and a length of 64 mm.

application

The best-known representative of a beam pentode is the 6L6 , which was initially brought onto the market by RCA in 1936 as a steel tube with an octal base, but was later manufactured as an all-glass tube in a glass bulb. The 6L6 was oversized for many applications, for example for car radios, therefore brought Kenrad end of 1936, the 6V6G out. With a single power tube of this type, A-mode amplifiers with an output power of approx. 5 watts could be produced. Other well-known representatives of this type of tube are the KT66 and the KT88 , introduced by the General Electric Company (GEC) in 1956 , which is often used in high-end high-end high-fidelity amplifiers .

In tube guitar amplifiers , the 6L6 or 6V6 beam pentodes (e.g. Fender ) are mostly used as output stage tubes in addition to the pentodes EL84 (e.g. Vox ) or EL34 (e.g. Marshall ) .

See also

Web links

Commons : ray pentodes  - collection of images, videos, and audio files

Individual evidence

  1. ↑ https://frank.pocnet.net/sheets/049/6/6146B.pdf Data sheet of the beam tetrode 6146B, accessed on Feb. 3, 2019
  2. ^ High Performance Audio Power Amplifiers , Ben Duncan, Newnes, 1996, ISBN 978-0-7506-2629-3 , p. 402 (en)
  3. ↑ a b https://archive.org/stream/IntroductionToRadarSystems/Skolnik-IntroductionToRadarSystems_djvu.txt Merrill I. Skolnik: Introduction to RADAR Systems , McGraw-Hill Book Company Inc., 1962, accessed on Feb. 1, 2019
  4. ↑ https://www.relltubes.com/products/Electron-Tubes-Vacuum-Devices/Tetrode/4X150A-7034EI.html Beam-Tetrode 4X150A / 7034 from Richardson Electronics , accessed Feb. 1, 2019
  5. ↑ https://frank.pocnet.net/sheets/164/4/4X150A.pdf Svetlana - replica of the 4X150A / 7034, data sheet, accessed on Feb. 1, 2019