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
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
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.