Note: Heath Z-Bridges (long)

[Michael Hopkins]

   The difference between a kit builder and a home brewer often hinges on
one machine: An Impedence Bridge.  Heath knew from the first that a small
market existed for these impressive looking devices and the line
stretches back to the earliest 1950s.

  The first I found, sitting on the pavement at a broadcast radio
collector's rummage sale, was a Heath Model IB-1B, from about 1952.  This
one sits in a wood case with a slight taper down.  The color is beige
like an AT-1 transmitter, but the lettering is red.  A small center
meter, seven small knobs, and one large one are features of the panel
with screw terminals for unknowns and for external AC detector.

   The IB-1B has no vaccum tubes at all, just a mechanical device to
generate a 1000 hz tone from a lantern cell.  It reads 0.01 Ohms to 10M;
10 pF to 100 uF and 10 uH to 100H.

  The Model IB-2A of 1958 assumes the familiar upright posture with a top
taper back from midline.  The picture on the manual I have looks like it
is gray, and it has two big knobs, two medium sized, and a bunch of
small.  Inside one finds battery tubes, 1U4 (2) and 1L4 (2) forming a
generator and a detector.  The center meter has grown but it only goes
down to 100 pf.

   By 1977 the Model IB-3128 has changed little from the '58 IB-2A, but
by then Heath is offering an allied product.  The QM-1 Q Meter of 1966
looks like an impedence bridge but has 180 degree scales on each side
that swing down and four binding posts on the top right.  There is a big
meter in the center for readings directly in Q plus 1 uH to 10uH and 40pf
to 400 pf.  There is also a built in RF generator tuning from 150 kc to
18 mc and tubes inside are 6AL5, 12AU7, 12AT7, OD3 and 6X5.

  Ham literature bristles with useful articles, but of special interest
to the Heath student is "All About Impedance Bridges," Burgess, H,
(W5WGF) CQ Magazine, Sep., 1945 p 43.  In this last of a series of on
test equipment, the author uses and illustrates a Heath IB-2.

de ab5L, michael in dallas, MNHopkins at JUNO.com
Student of ICM, Tecraft and 6M's Golden Age: 1956-58
Box 226841, Dallas, 75222    Hr '66 QM-1

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