Heathkit TT-1 - Page 3

INTRODUCTION
A vacuum tube possesses a number of operating
character istics, any one of which may be used to
indicate operational capabilities of the tube. Any
number of tube testing devices are available,
utilizing one or more of these characteristics,
each one subject to its own limitations. It is
universally recognized that no tube tester can
provide a complete and accurate account of the
condition existing within a given vacuum tube
when that tube is in operation in the equipment.
If maximum benefit is to be obtainedfrom a tube
TARA TANT SATA
DLIVLLOOLUL
Testing the emission capabilities of the cathode
provides the simplest and most economical
means of determining the overall quality of a
vacuum tube. This is accomplished by connecting
all the grids to the plate and operating the tube
as a rectifier. The actual emission of the cathode
is then compared to a predetermined value
accepted as standard for that tube type. If the
cathode should have one particularly active
portion, the emission checker will indicate the
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quality of the tube to be good, even though the
A transconductance tester places a standar
voltage on each tube element, creating a plate
current flow. Measurement of this piate current
will indicate the transconductance of that par-
ticular tube under static conditions. Here again,
DYNAMIC TRANSCONDUCTANCE TESTING
The dynamic transconductance of a tube is
measured by using the circuit of the static
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transconductance tester and adding a signal
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tube under test, the action of the plate current
will be similar to that experienced in the re-
ceiver, varying in relationship to the input signal.
This system gives an indication of how the tube
EQUIPMENT TESTING
No tube tester is required in this system of tube
testing; simply insert a new tube in the equip-
ment and observe the results. At first glance
this appears to be the most inexpensive testing
tester, regardless of its design, two things should
be known:
the requirements placed on the tube.
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1.
2. the limitation: th
oO
or
od,
With this thought in mind, we have listed some
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OL tie more commonly used methods of tube
testing.
remainder of the cathode may be inactive. On
the other hand, modern coated cathodes are
capable of large emission, often far in excess of
the emission required for the particular applica-
tion. In some cases the emission checker will
indicate the quality of the tube to be questionable
or even unacceptable. ‘This tube may not function
would ‘probably operate satisfactorily for a long
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time in a circuit where the emission r
ments are less stringent.
Since
the
tube
is
not
operating
EXACTLY
as
it
does
in
the
equipment,
the
test
may
be
termed
inconclusive.
An
improved
version
of
the
trans-
conductance
test
is
available
in:
will
operate
under
signal
conditions,
but
is
still
somewhat
limited.
Certain
types
of
tubes
cannot
be
completely
checked
on
any
type
of
tester,
even
the
dynamic
transconductance
tester.
Par-
ticular
offenders
in
this
respect
are
tubes
used
in
the
vertical
and
horizontal
deflection
circuits
of
television
receivers.
The
only
method
of
accurately checking these tubes is by:
system available. Bear in mind, however, that if
all tubes were to be tested in this manner, a
stock of tubes representing an investment of
several hundred dollars would be reauired.
Page 3
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