. Electronic apparatus for biological research . R2 R3 Ri, 220kfi lOkO 22kQ 300 Q Pre-set 3W ;?5 2k Q Pot 3W C3 8pF500V Wkg /?6 A7kQ5W 1/1 Ferranti CL-iO Ch 20 henries V2 Ferranti 807 CI 50iiF 50V Wkg 1/3 Ferranti R52 C2 16p,F500V Wkg Figure A recommended circuit for controlling a CL40 linear light source Cathode-ray oscilloscope sources The widespread use of the cathode ray oscilloscope in the modern labora- tory often provides a convenient opportunity to use the as a modulated light source for experimental purposes. It offers the advantages of slow or fast adjustment of the posi
. Electronic apparatus for biological research . R2 R3 Ri, 220kfi lOkO 22kQ 300 Q Pre-set 3W ;?5 2k Q Pot 3W C3 8pF500V Wkg /?6 A7kQ5W 1/1 Ferranti CL-iO Ch 20 henries V2 Ferranti 807 CI 50iiF 50V Wkg 1/3 Ferranti R52 C2 16p,F500V Wkg Figure A recommended circuit for controlling a CL40 linear light source Cathode-ray oscilloscope sources The widespread use of the cathode ray oscilloscope in the modern labora- tory often provides a convenient opportunity to use the as a modulated light source for experimental purposes. It offers the advantages of slow or fast adjustment of the position of the source, of adjustable source size and, of course, precise modulation of the intensity. A number of phosphors are now in use for cathode ray tubes. The spectral energy distribution of the type B screen (Mullard Ltd.) is shown in Figure It is the screen usually used when photographic records are required. Its spectral output matches very well the type S4 photo- cathode used in many photocells, the 931 A photomultiplier tube. It has a short duration phosphorescence, the light output dropping from 100 to 10 per cent in 3 msec and to 1 per cent in 9 msec. Type F and L screens are green in colour and are preferable for visual monitoring. They have a moderately long afterglow time, the light output falling from 100 to 10 per cent of luminance in about 20 seconds. Type W is used for television screens and is a mixture of several phosphors to give a near-white visual impression. Type R is a long-persistence screen developed for radar displays, but useful in the biological laboratory for studying slow non-repetitive events such as the electrocardiogram {Figure ). 352
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