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REPLACEMENT OF BATTERIES
Place the meter upright on a table, loosen the two screws in the cover plate
(at the rear) three-quarter turn and remove the cover plate (by Aiding it
upwards a little and then pulling it forward).
The batteries can now be removed from the meter casing (if necessary, the
smallest with the aid of a thin screwdriver) and replaced by fresh ones?
Make sure that the + terminals of the batteries make contact with the contact
springs marked + in the meter casing.
Finally refit the cover plate.
Remark: When replacing batteries, never use the so-called leak-proof
type, as the steel jackets of this batteries influence the deflection of the
needle of the measuring instrument.
SOME EXAMPLES OF MEASUREMENTS
A'. Direct-voltage measurements
For measuring direct voltages in a receiver or amplifier, the negative side of
the meter must be connected to the negative pole of the voltage. The
measuring probe at the positive side of the meter is brought into contact
with the points to be measured, e.g. with the electrodes of the valves (anode
and screen-grid voltages) or with the electrolytic capacitors in the
smoothing circuit.
B'. D.C. Measurements
The anode current of an output valve can be measured very conveniently by
placing the two probes on the primary terminals of the output transformer.
As the internal resistance of the meter is low compared with the ohmic
resistance of the primary of the output transformer, the anode current will
flow through the meter and not through the transformer.
For checking the operation of an oscillator valve, the current through the
grid-leak resistor is measured. To "do this, disconnect the junction at the
"earthed" side of this resistor and connect the probe of the meter to the
the cathode of the oscillator valve.
resistor and the + probe to
If the grid current of an oscillator valve is e.g. 200 µA, a clear reading can
be obtained in the 0.6 mA range.
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