Service Manuals, User Guides, Schematic Diagrams or docs for : . Rare and Ancient Equipment Palec palec_original_valve_data_book0001
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METHOD OF VALVE TESTING.
J1ust what constitutes the best method of testing a valve to determine
its general condition, has been the subject of much discussion among
radio engineers.
Opinions at one time were divided between the relative efficiency of
the four existing methods viz: the true mutual conductance, the power
output, the grid shift and the emission test.
An avalanche of new valves settled the controversy 1>ybringing the
emission tester into general favour as a commercial valve tester because
it was the only system which could be adapted to incorporate all the
following points:
l---.Ability to cope with the hundreds of existing valves as well
as future releases.
2--Simplicity and quickness of operation.
S-Reasonably low selling prices.
4--.Pract.ic~1 accuracy.
The true mutual conductance tester. whilst the most accurate, IS
purely a laboratory instrument requiring as many controls and meters
as there are elements in a valve. Therefore it can be regarded as im-
practicable for commercal purposes.
The Imitation of the so-called "grid shift," and power output systems,
combined with the fact that a well designed emission tester may ~e the
more accurate, has brought the latter into universal use. It will be
realised that the only thing likely to happen to a radio valve in service,
(apart from leakage between elements) is a depreciation of the emitting
qualities of the ell-thode element. So why not test a tube for ita emissioD
current? ,
-
~
.~
This' has been confirmed by our own and overseas laboratory eom-
When the emission type valve test was first developed, the mistake
was made of applying a high voltage to the valve through a voltage
dropping resistor. Consequently, the voltage applied to the valve (tested
as a diode) depended on the current drain. This. meant that a poor valve -
which had a low emission, was tested at a higher potential than a. good one
and that true differences of merit could not be arrived at. Then a&ain,
there arose the danger of harming a poorish valve through excessive vol~ .
age being applied to the grid and injuring the cathode coating.
In the "Palec" valve tester, a constant low voltage is applied and th.
current drain limited to well below satura tion point.
This low voltage is not sufficent to ionise gas if present in a valve
_ .
,
and produce extra emission. Consequently, the "Palec" valve tester ir
a true emission tester and shows the true condition of the cathode.
With regard to a gas test, it must be remembered that the percentage
of gassy valves is low among new valves, as the manufacturers are UlualJ,
careful that no such valves leave their factory.
The percentage of valves which become gass'y with use is' alao
extremely low, Iess than z % actually.
Before a valve becomes gassy, it must usually be seriously over-
loaded. This overloading causes a drop in the emission rapabilitiea of
the cathode. The condition is detected by our-tester.
Thus, the tester does, in almost every caee, class a gasSy tube as poor.
Oil account of its usually showing poor emission under the test applied.
METHOD OF CALIBRATING "PALEC" MODEL V.C.T.
Manufactured by
VALVES NOT USTED
PATON ELECTRICAL PROPRIETARY LTD.
Take tw~ or three Valves of any particular type of which the cali-
FOREWORD
bration figures are required and follow this procedure:-
(1 Check line voltage in the usual manner, The object of Paton Electrical Proprietary Ltd., in releasing the
(2) Turn Filament Selector Switch to the voltage at wlJch the "Palec" Model V.C.T. is to place in-the hands of the serviceman, a single
particular tube is rated. self-contained instrument that will adequately cope with all general out-
side service problems and yet be conveniently portable.
(3) Turn left bottom Switch to Merit test, turn Range Control to The instrument will be found extremely easy and quick to operate
about five and plug in valve. (Be sure to connect up the grid cap, if any). and can be relied upon for a high dgree of accuracy if treated with
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