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POWER SUPPLY FOR SOUND SYSTEMS 505
rectifier circuits built into modern amplifiers to provide them with high-voltage "IV current.
(are of Tube Rectifiers
A rectifier such as that shown in Figures 115 and 116 requires very little attention. (25) The relay contacts of S-l and S-2 should be burnished occasionally to insure that they make firm and solid connection.
Excessive heating of any part should of course be investigated immediately. Such over-heating may be caused by excessive current drain that must be corrected. It may be caused by a growing defect inside the coil or condenser in question, in which event a duplicate part must be procured at once. It may also be caused by a defective connection to the part, which should be resoldered. The cause need not be at the point where the overheating occurs, but can be a defectively low resistance in any other portion of the same circuit.
(26) In the event of any coil or condenser of the filter system burning out, when no spare is available for immediate replacement, a satisfactory temporary repair can usually be effected by borrowing storage batteries from the nearest charging station and connecting them in parallel to the damaged circuit. A sufficient number of cells should be connected in series to make the voltage of the battery as a whole equal to the voltage of the d. c. line in question. A storage battery "floating" across a d. c. line constitutes one of the best of all filters for slight to medium ripple.
(27) The tubes of this type of rectifier require some attention. If either one burns out, that event will be indicated by a marked drop in the power supplied, as well as by a strong hum in the sound ; the latter resulting from the fact that the unit is then operating on one tube only, as a half-wave rectifier, with a correspondingly heavier ripple which the filter is not designed to remove.
Hum will also be heard if one tube, through age or for any other reason, becomes much less efficient than its partner. In that case the good tube is carrying the greater part of the load, and the unit functions essentially