Hickok 539C - Additional Test Procedures; Tube Life Testing Procedure; Self-Bias Testing; Plate Current Measurement

The Model 539C is valuable in matching tubes for push-pull stages and other appli-
cations where matched tubes are essential.
15. Life Test. The Model 539C DYNAMIC MUTUAL CONDUCTANCE TUBE TES-
TER is equipped with a special feature to enable Life Test to be made on the tube. In the
center of the control panel is a switch designated CATH. ACT., NORM. and TEST. While
holding
everything else at normal this switch reduces the filament voltage by 10%.
a. Measure the mutual conductance in the ordinary way with switch set on NOR-
MAL.
b.
Throw the CATH. ACT. switch to TEST position. The mutual conductance
should not drop more than 20%.
c. After making life test return the switch to NORMAL for all other tests.
In testing the 35Z5 and 45Z5 rectifier tubes it is advisable to turn the power off for
about 15 seconds after throwing the CATH. ACT. switch to TEST to allow the cathode to
cool.
Then turn the power on and note new reading of the meter.
16. Self Bias. Provision is made to test tubes under self bias condition. In the up-
per edge of the control panel are two binding posts designated SELF BIAS. These posts
are normally shorted by an attached bar. To use SELF BIAS, connect a suitable bias re-
sistor together with an electrolytic capacitor of 2000 I.Ltd in parallel across these binding
posts. The positive terminal of the capacitor should be connected to the positive binding
post.
The toggle switch in the upper left of the control panel is thrown from NORMAL po-
sition to the SELF BIAS position. The bias volts under self bias condition depends upon
the value of the resistor inserted between the self bias posts mentioned above, and also
upon the plate current flowing.
Tube handbooks can be used as a guide to the value of the self bias resistance to use.
When completing the self bias test, reconnect the two binding posts by the normal short-
ing bar and throw the toggle switch back to the NORMAL position.
17. Plate Current. In the upper center of the control panel are two posts designated
PLA TE CURRENT. These posts are normally shorted by an attached bar. A suitable
low resistance D. C. milliammeter connected across these posts will measure the plate
current flowing through the tube being tested. Connect the positive terminal of the meter
to the positive binding post.
NOTE
A D. C. milliammeter connected into the SELF BIAS
circuit will measure the total cathode current. In
measuring rectifier tube current the meter reading
must be multiplied by two, because rectifier tubes
conduct only during a positive half-cycle, whereas
the meter integrates over a complete cycle.
In checking thyratrons such as the 884 and 885, the bias voltmeter should be set
initially at its highest negative value (about 40 volts). The designated button is held down
while the bias voltage is gradually reduced until the tube" strikes", that is, begins to con-
duct, which is indicated by a sudden deflection of the meter. The chart indicates the ap-
proximate voltage at which the tube strikes. There may be a small variation above or be-
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