. Electronic apparatus for biological research . Figure Figure circuits of a long-tailed pair (Figure ). When the grids are at the same potential the neons should glow at equal brightness. The input impedance of the device is, of course, very high, and it has the merits of rapid response and indestructibility. Per volt of potential difference at the input, one lamp brightens, and the other dims, by about 0-05 Im. With both grids earthed, each lamp emits about 0-06 Im. Hence with one grid made J V positive to earth and one | V negative, the light outputs become 0-11 and 0-01 Im, s
. Electronic apparatus for biological research . Figure Figure circuits of a long-tailed pair (Figure ). When the grids are at the same potential the neons should glow at equal brightness. The input impedance of the device is, of course, very high, and it has the merits of rapid response and indestructibility. Per volt of potential difference at the input, one lamp brightens, and the other dims, by about 0-05 Im. With both grids earthed, each lamp emits about 0-06 Im. Hence with one grid made J V positive to earth and one | V negative, the light outputs become 0-11 and 0-01 Im, so the device is quite sensitive. 'MAGIC EYE' NULL-DETECTOR Another null-detector^, employing single-sided circuitry, uses the familiar 'magic eye' valve, generally used for facilitating the tuning of radio receivers. Like the neon lamps these valves have the advantage over meters of instant response and electrical indestructibility. The circuit is shown in Figure With zero input voltage the shadow angle of the magic eye is 85 degrees. An input of either polarity then narrows the shadow angle; 1 V positive reduces it to 55 degrees and 1 V negative to 30 degrees. 451
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