science

Suppressor grid

Suppressor grid is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Suppressor grid rather than just read about it. In short: A suppressor grid is a wire screen used in a thermionic valve (i.e. vacuum tube) to suppress secondary emission. It is also called the antidynatron grid, as it reduces or prevents dynatron oscillations.

Key takeaways

Suppressor grid belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Suppressor grid to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Suppressor grid from memory before moving on to harder problems.

Reference excerpt

A suppressor grid is a wire screen used in a thermionic valve (i.e. vacuum tube) to suppress secondary emission. It is also called the antidynatron grid, as it reduces or prevents dynatron oscillations. It is located between the screen grid and the plate electrode (anode). The suppressor grid is used in the pentode vacuum tube, so called because it has five concentric electrodes: cathode, control grid, screen grid, suppressor grid, and plate, and also in other tubes with more grids, such as the hexode. The suppressor grid and pentode tube were invented in 1926 by Gilles Holst and Bernard D. H. Tellegen at Phillips Electronics. In a vacuum tube, electrons emitted by the heated cathode are attracted to the positively-charged plate and pass through the grids to the plate. When they strike the plate they knock other electrons out of the metal surface. This is called secondary emission. In the four-electrode vacuum tube, the tetrode, the second grid, the screen grid, is operated at a positive voltage close to the plate voltage. During portions of the cycle when the plate voltage is below the screen grid voltage, secondary electrons from the plate are attracted to the screen grid and return to the cathode through the screen grid power supply. This flow of electrons away from the plate causes a reduction of plate current when the plate voltage increases, in other words the plate has a negative resistance with respect to the cathode. This can cause distortion in the plate waveform and parasitic oscillations called dynatron oscillations in an amplifier. In the pentode, to prevent the secondary electrons from reaching the screen grid, a suppressor grid, a coarse screen of wires, is interposed between the screen grid and plate. It is biased at the cathode voltage, often connected to the cathode inside the glass tube. The negative potential of the suppressor with respect to the plate repels the secondary electrons back to the plate. Since it is at the same potential as the cathode, the primary electrons from the cathode have no problem passing through the suppressor grid to the plate. In addition to preventing the distortion of plate current, the suppressor grid also increases the electrostatic shielding between the cathode and plate, causing the plate current to be almost independent of plate voltage. This increases the plate output resistance, and the amplification factor of the tube. Pentodes can have amplification factors of 1000 or more.

References

Worked examples

Example 1 — a first encounter with Suppressor grid

Start with the simplest possible case. Write down what Suppressor grid claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Suppressor grid before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Suppressor grid ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Suppressor grid

In research: Suppressor grid appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Suppressor grid in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Suppressor grid is common in secondary-school and first-year university syllabi. It links to neighbouring topics Electrodes, Vacuum tubes, so understanding it makes those chapters shorter.
In everyday life: Look for Suppressor grid outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Suppressor grid in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Suppressor grid means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Suppressor grid out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Suppressor grid in simple terms?

Why does Suppressor grid matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Suppressor grid?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Suppressor grid.