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1.1 Purpose and Usefulness. Designed specifically to meet the need of television and radio technicians for a compact, reliable, and simple-to-use instrument for testing all types of capacitors, the Sprague Model TO-4 Tel-Ohmike represents the culmination of years of experience in this field. It incorporates in one instrument an accurate multi-range capacitance and power factor bridge, an insulation resistance checker for paper, mica, and ceramic capacitors, a leakage current test circuit for electrolytic capacitors, and a a-c resistance bridge for measuring resistors. Pushbuttons are provided for instant range selection and a magic-eye tube simplifies bridge balancing for capacitance and resistance measurements. A large meter gives direct pointer readings of insulation resistance and leakage current and shows the exact voltage applied to electrolytic capacitors during the leakage test. 1.2 Three especially valuable features of the Model TO-4 Tel-Ohmike are the extended insulation resistance test range up to 20,000 megohms, the special low capacitance bridge circuit for checking low value ceramic and mica capacitors from 1 mmf to 100 mmf with improved accuracy, and the automatic discharging of capacitors after test by a simple release of all push buttons. 1.3 Capacitance. In addition to the special low range mentioned above, 4 other capacitance ranges are provided for measurements up to 2000 mf. With a TO-4 Tel-Ohmike you are prepared for every capacitor from tiny ceramics and micas to paper capacitors to all types of dry electrolytics from small Filter capacitors to extremely high capacitance low-voltage units and motor-starting capacitors. 1.3.1 Power Factor. The power factor of all electrolytics is indicated directly on a scale. Three ranges are provided for improved accuracy of reading. 1.4 Leakage Current. A self-contained continuously adjustable d-c Power supply permits measurement of electrolytic capacitor leakage current at exact rated voltage. 1.5 Insulation Resistance. The electronic measurement circuit reads I-R directly from 150 to 20,000 megohms, covering the wide range necessary for testing ceramic, mica, air, and paper capacitors. With a Model TO-4 Tel-Ohmike it becomes a simple matter to detect "leaky” coupling capacitors. 1.6 Resistance. Three ranges are provided for line-frequency bridge measurement of resistors from 2.5 ohms to 25 megohms. 1.7 Line Voltage and Frequency. The Model TO-4 Tel-Ohmike is available in two types. The standard TO-4 is intended for 115 volt, 50-60 cycle a-c lines. Also available is the Model TO-4X for use on 115/230 volt, 25-60 cycle mains. Before using a Model TO-4X, check to see whether the link on the internal terminal plate is in the proper position for the line voltage on which the instrument will be used.