Heathkit VC-3 Instruction Manual

HOM rev. new
Heathkit of the Month:
by Bob Eckweiler, AF6C
Heathkit VC-3
Voltage Calibrator.

Introduction:

The August 2013 Heathkit of the Month (#51)
covered the IG-4505 Deluxe Oscilloscope Cali-
brator. It also briefly covered the VC-3 Voltage
Calibrator using information gleaned from cata-
logs. To my surprise Bill - K6WHP recently pre-
sented me with a VC-3 complete with manual.
One look at the unusual schematic and I knew it
deserved an article all its own.
The VC-3 (Figure 1), third in the Heathkit line
of oscilloscope voltage calibrators that were
first introduced in 1952, appeared in late 1956.
Figure 2 shows an ad for the Heathkit VC-3
from the 1958 catalog. It remained in produc-
tion through 1962 at a price of $12.50. In those
days the oscilloscope was the most prolific of
Heathkit's products. From the O-1 oscilloscope
(Heathkit's first electronic kit) introduced in
September of 1947 through the end of 1956
Heathkit sold 14 different models, the O-1
through O-11, the OL-1, the OM-1 and OM-2.
All had 5" CRTs except the OL-1 (3"), and all
had AC coupled amplifiers and multivibrator
sweep circuits. DC coupling and triggered
sweep were on the horizon for Heathkit, but
Figure 2: Heathkit VC-3 ad from the main 1958 Catalog
Copyright 2015, R. Eckweiler & OCARC, Inc.
Heathkit of the Month #64 - VC-3 Voltage Calibrator
Figure 1: Heathkit VC-3 Voltage Calibrator
not yet incorporated. The first Heathkit oscillo-
scope featuring these improvements came in
the fall of 1958, the OP-1 Professional Oscillo-
scope Kit. It sold for $179.95, about 2-1/2 times
more than their previous top-of-the line
Heathkit oscilloscope.
The Heathkit VC-3:
Prior to the OP-1, most of the hobby-grade os-
cilloscopes on the market had at best a 1 volt
peak-to-peak test point that one could use to
approximate the voltage of a wave form. Since
the gains were mostly uncalibrated and the at-
tenuator steps a full decade apart, measuring
voltage was difficult without a way to compare
it with a known signal. The VC-3 provides the
ability to make that comparison easily.
The VC-3 puts out a rather impressive ap-
proximate 1 kc square wave that has an accu-
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