. The principles and practice of roentgenological technique . current supply, then the filamenttransformer is to be recommended. A smallrotary convertor may be utilized where onlydirect current is available, to supply alternating-current to the filament. If a battery is used it should be a 5- or 6-cell(10- or 12-volt), 40 ampere-hour battery andarrangements should be made so that the bat- [68] COOLIDGE TUBE CIRCUIT 69 tery can be connected during the night to acharging circuit. In order to allow the bat-tery to reach a stable condition and eliminatefluctuations in the filament current, the fil
. The principles and practice of roentgenological technique . current supply, then the filamenttransformer is to be recommended. A smallrotary convertor may be utilized where onlydirect current is available, to supply alternating-current to the filament. If a battery is used it should be a 5- or 6-cell(10- or 12-volt), 40 ampere-hour battery andarrangements should be made so that the bat- [68] COOLIDGE TUBE CIRCUIT 69 tery can be connected during the night to acharging circuit. In order to allow the bat-tery to reach a stable condition and eliminatefluctuations in the filament current, the fila-ment circuit should be closed a few minutesbefore the tube is used. (A fully charged bat-tery shows volts per cell, dropping rapidlyto a stable point of 2 volts.) It is advisable tocharge the battery at frequent intervals,owing to its instability of voltage. If long battery leads become necessary, theyadd resistance to the filament circuit, so thateither additional cells must be added or heavierwire leads used. It must ahvays be borne in mind that the. Fig. 86.—Step-down transformer and interrupter foruse with Coolidge filament. (Jordan.) entire battery circuit is brought to the fullpotential of the tube and that it, therefore, hasto be as thoroughly insulated from the patientand the ground as the tube itself. Jordan has suggested the use of an inter-rupter in conjunction with a small step-downtransformer. A rheostat in the primary circuitprovides the regulation. A motor-magneticinterrupter is used. A full Coolidge circuit is shown in diagram,Figs. 87, 89, in which the double reel goes tothe cathode end of the tube, one lead to theamperemeter the other to the secondary of thestep-down transformer. The rheostat for con-trolling the current in the filament circuit is inthe primary. A small rotary converter is usedwhere only d. c. is available. The technique forthe Coolidge tube work demands the use ofan ammeter in the filament circuit. The metershould have a 5-ampere scal
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