1.1 Purpose and Usefulness. Designed specifically to meet
the need of television, radio and industrial electronics
technicians for a compact, reliable, and simple-to-use
instrument for testing capacitors, the Sprague Model TO-6A
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, plastic-film, mica,
and ceramic capacitors, and a leakage current test circuit
for electrolytic capacitors. Pushbuttons are provided for
instant range selection and a magic-eye tube simplifies
bridge balancing for capacitance 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 Six especially valuable features of the Model TO-6A
Tel-Ohmike are: (1) the I-R (insulation resistance) range of
500 Mii-50 KMQ, (2)a special I-R range of 100 Mo-10
KM£i(with a 25 volt circuit for low-volt-age capacitors),
(3) the special low-capacitance bridge circuit for testing
low-value ceramic, mica, plastic-film, and air dielectric
capacitors from 1-
100 pF with improved accuracy, (4) the meter protection
which prevents "burn-outs” should the meter be overloaded,
(5) the Safety switch for easier discharge of capacitors
after test, and (6) the "eye” amplifier to provide greater
1.3 Capacitance. In addition to the special low range
mentioned above, 4 other capacitance ranges are provided for
measurements up to 2000 /xF. With a TO-6A Tel-Ohmike you are
prepared to te$t every type of capacitor from tiny ceramics
or micas to paper and film capacitors of all types, as well
as electrolytics—tantalum or aluminum—wet or dry—low voltage
or high voltage—small capacitance or large capacitance—from
small filter types to large motor-start or photoflash types.
1.3.1 Power Factor. The power factor of all electrolytic
capacitors is indicated directly in percent on a single scale. ?
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. Most paper, plastic-film,
ceramic, mica, and air dielectric capacitors have their I-R
measured by a circuit which applies 150 volts to the
capacitor, and the I-R is indicated directly on the
meter dial from 500 Mii to KMq. For testing non-electrolytic
capacitors rated at less than 150 volts, an additional range
of 100 Mii to 10 KM£J is provided in conjunction with a
circuit which applies only 30 volts to the capacitor under test.
1.6 Line Voltage and Frequency. The Model TO-6A Tel-Ohmike
is available in four types. The standard TO-6A is intended
for 115 volt, 50-60 Hz a-c lines. TheTO-6ARM is similar
except that it is intended for mounting in standard 19"
relay racks. Also available is the Model TO-6AS for use on
115/230 volt, 50 Hz mains. Before using a Model TO-6AS,
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. A rack-mounting version, the
TO-6ASRM, is also available.