Heathkit IM-18 - Introduction to the VTVM

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105-125
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210-250
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50/60
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10
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Cabinet
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7-3/8"
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4-11/16"
wide
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4-1/8"
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The Heath Company reserves the right to discon-
tinue instruments and to change specifications
at any time without incurring any obligation to
incorporate new features in instruments pre-
viously sold,
INTRODUCTION
The HEATHKIT Model1M-16 Vacuum Tube Volt-
meter is intended for use by servicemen, en-
gineers, and maintenance men to make accurate
measurements of DC+, DC-, AC rms and peak-
to-peak voltages, plus resistance, The design is
simple and rugged, yet accurate,
The instrument employs vacuum tubes for recti-
fication and amplification on all measurement
functions to insure good sensitivity and stability
of operation, Precision resistors are usedinthe
voltage divider networks to provide high accu-
racy,
The confusing tangle of test leads coming from
the front panel of most VT'VMs is eliminated by
the use of a combination AC-OHMS-DC switching
test probe and a single jack input connection for
both test probe and ground leads, The 1 megohm
resistor in the probe is switched into operation
when the probe switch is set on DC, This iso-
lating resistor allows DC component voltages to
be measured separately, even when high fre-
quency AC voltages are present at the test point,
The VTVM has a very high input impedance (11
megohms on DC and 1 megohm shunted by 35
unt on AC), Consequently, the circuit in which
the voltage is being measured will not be sig-
nificantly loaded by the VT'VM, Most nonelec-
tronic voltmeters (VOM) have a much lower in-
put impedance over the most frequently used
ranges of test voltages, Consequently, when a
VOM is used to measure voltages in high im-
pedance circuits, the indicated voltage will be
appreciably less than the actual voltage, The
amplifier section of the VTVM also enables the
VTVM to accurately measure much higher re-
sistances than can be conveniently measured
with a VOM,
Read the "Kit Builders Guide” for complete
information on unpacking, parts identification,
tools, wiring, soldering, and step-by-step as-
sembly procedures,