. Electronic apparatus for biological research. Electronic apparatus and appliances; Biology -- Research. THYRATRON determined largely by the limiting resistance R (Figure ), and the voltage across the valve falls to the ordinary ionization potential, about 15 V. The current is in fact (K— 15)/^; a typical small thyratron will pass up to 100 milliamps. As a result of the current of positive ions travelling towards the cathode region, not only is the space charge cancelled, but also the effect of the negative grid, and it is impossible to shut off the discharge by making the grid more negat
. Electronic apparatus for biological research. Electronic apparatus and appliances; Biology -- Research. THYRATRON determined largely by the limiting resistance R (Figure ), and the voltage across the valve falls to the ordinary ionization potential, about 15 V. The current is in fact (K— 15)/^; a typical small thyratron will pass up to 100 milliamps. As a result of the current of positive ions travelling towards the cathode region, not only is the space charge cancelled, but also the effect of the negative grid, and it is impossible to shut off the discharge by making the grid more negative since the only effect this has is to attract more ions into the cathode region. We say that the grid 'loses control'. Instead of fixing -o +v. Figure the grid bias and raising the anode potential until ionization occurs, we can of course fix the anode potential at some value greater than the ionization potential and initiate conduction by raising the grid potential from very negative to [anode potential]/[control ratio]. When this is done (bearing in mind that it subsequently loses control) the grid is said to be being used as a 'trigger' and—extending the analogy—when ionization occurs the thyratron is said to 'fire'. The only way to stop the discharge again is to reduce V below the ionization potential. Precautionary measures to be taken with thyratrons are similar to those for soft hot-cathode diodes. The cathode must be allowed to warm up before the anode potential is applied, and the discharge current must be held within the makers' upper limit, for fear of destroying the cathode. Thyratron relaxation oscillator—One difficulty with the difference diode relaxation oscillator is that the amphtude of the three outputs cannot readily be controlled electronically. Output (1) is fixed by the voltage-diff'erential of the tube, and outputs (2) and (3) by the relative sizes of R^ and R^, {Figure ). The thyratron relaxation oscillator can be controlled by a pote
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