Disc triode

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Disc triode (Soviet Union approx. 1978), e.g. B. for VHF radio about 100 watts

A disc triode is an electron tube (triode) in which the electrodes (cathode, control grid and anode) are not arranged in a cylindrical manner, as is usually the case, but in the form of a disc with a small spacing one above the other.

The electrodes are connected to concentric metal rings for low-induction contact so that these tubes are especially suitable for high-frequency applications.

Disc triodes are usually installed in coaxial line circuits in a basic grid circuit and can be used for amplification or as an oscillator at frequencies of up to about 5 GHz.

Disc triodes are only occasionally used today in the area of ​​higher power.

construction

small disc triode of Soviet manufacture (09/1977) from an FMCW radar altimeter

The electrodes, which are provided with metal rings, are separated from one another by insulator rings (glass or ceramic) and are hermetically sealed to one another with glass or silver solder.

Disc triode for up to approx. 2 GHz, so-called "lighthouse tube"

The resulting tower-like structure led to the designation "lighthouse tube" for some tube types.

The metal-ceramic connections are u. a. Due to the thermal stress, technologically much more demanding than the manufacture of conventional tubes with pin bases. The comparatively small volume of the vacuum, the lack of space for a getter and the high field strengths require the connections to be tightly sealed in order to maintain a good high vacuum.
In addition, the distance between the grid and the cathode is often very small in order to achieve a high steepness. Often these are slightly curved to increase rigidity.
The distance between the anode must also be small in order to keep the transit time delays and velocity dispersion of the electrons low.

Disc tetrodes are specially manufactured for high outputs; these also have a screen grid between the control grid and anode.

Small disc triodes are cooled by heat conduction through the connections. The larger specimens (mostly disc tetrodes) have specially designed anode blocks for better cooling: they are available with cooling fins for forced air cooling or with hose nozzles for liquid cooling .

Applications

Disc tetrode (GU-43B, Soviet Union 1976), 1500 watts, up to 100 MHz, air cooling

Disk triodes were used in high-frequency amplifiers and oscillators in the field of small and medium power until the 1980s. For outputs from around 1 kW they are still common today - but then mostly designed as tetrodes.

Disk triodes can withstand high mechanical acceleration values, a wide temperature range as well as nuclear and cosmic radiation , which is why they have long been in use in the aerospace and military technology in the low power range.

The NATO has frequently used until the 1990s, a Scheibentriode type 2C39BA in their aircraft. These and other tubes of the same design are still used by radio amateurs in transmission amplifier stages up to the GHz range because they have been readily available and inexpensive for years.

Examples:

  • FM radar (altimeter): mechanically frequency-modulated triode oscillator around 1 GHz
  • Mixer oscillator and preamplifier in long-range RADAR systems (around 1 GHz)
  • On-board radio in the VHF range

Today, disc tetrodes in particular are also used in high-power industrial HF generators.