component being probed is intermittent or
breaking down, the noise is continuous and
that component needs to be replaced. This
method can even detect cold soldered joints.
Heath Signal Tracer History:
To get an idea of what a valuable troubleshoot-
ing device the signal tracer is, Heathkit intro-
duced their first model, the T-1 in May of 1948,
and continued to manufacture updated models
until Heath went out of the kit business in the
early nineties.
Heathkit T-1:
The original Heathkit T-1 uses three octal
tubes: a 6SJ7 audio amplifier, a 6K6 audio out-
put and a 6X5 power supply rectifier. The RF
probe contains a crystal diode and connects to
the T-1 by banana plugs. The original T-1 cost
$19.50 and remained in production for eleven
months until April of 1949, when it was re-
placed by the T-2.
Ad for the Heathkit T-1 from an October
1948 Heath flyer
Heathkit T-2:
The T-2 is similar to the T-1 except it uses a
6SH7 audio amplifier tube and has a multi-
position switch that allows numerous different
matching impedances when using the speaker
output transformer externally. The cost re-
mained $19.50. It remained in production un-
til October of 1952 when it was replaced by the
T-3.
Heathkit T-3:
When Heathkit introduced the T-3 Signal
Tracer in 1952 they made many significant
changes that brought the tube count up to five.
The 6X5 remains as the power supply rectifier.
The rest of the tubes were changed to 12-volt
filament types. The 6K6 audio output tube was
changed to a 12A6 and the 6SH7 audio ampli-
fier to a 12SH7. The T-3 has separate inputs
(and probes) for audio and RF. The RF section
has an additional stage of gain using a 12C8
tube. On the T-1 and T-2 there is no visual indi-
cation of signal level; however they have jacks
where you may connect a VTVM. This changed
on the T-3 with the addition of a 1629 "Magic
Eye" tube. The 1629 was used in the WW-II
Command Set transmitters and was very com-
mon and inexpensive on the surplus market at
that time. The eye-tube provides indication of
relative signal strength. The T-3 also has an
unusual feature. It can measure the power con-
sumption of the DUT. The device is plugged
into a special AC outlet on the T-3 and turned
on. Once the device warms up, a control on the
T-3 is adjusted until the eye just closes but does
not overlap. The power consumption of the
DUT can then be read on the scale of the con-
trol. The 12C8 RF amplifier doubles as a diode
for the wattmeter function. The added features
of the T-3 raised its original price to $22.50.
The T-3 remained in production until the end
of 1957 when it was replaced by the T-4.
Heathkit T-4:
The T-4 was a totally new design. The price of
the T-4 dropped back below $20 and it re-
mained in production until 1962 when it was
given a new cabinet color scheme and renamed
the IT-12. Other than the new case the two cir-
cuits are identical.
Heathkit IT-5283:
In Early 1978 Heathkit stopped production of
the IT-12. In its place they introduced a line of
five solid-state low-cost test equipment pieces
that run on batteries or a common power sup-
ply. This is the 5280 line and includes the IG-
5280 RF Oscillator, IB-5281 RCL Bridge, IG-
Heathkit of the Month #9 - IT-12 Signal TracerHOM
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