Hickok 539C - Meter Functions and Special Tests; Ohmmeter Functionality; Normal and Low Plate Voltage Settings; Heater Current Measurement

m. a. range of the bias meter.
1. For the OA3 example adjust the m. a. current from 5 to 40 milliamperes by
turning the V. R. volts and mils knob. The OA3 tube should-not exhibit a
voltage change of more than 5 volts.
m. When completing a V. R. tube test unlock P4 push button.
20. Ohmmeter Feature. The Model 539C tube tester can be used as a utility ohm-
meter as follows:
a. Set the SHORTS switch on position B.
b. Connect two prod leads into the grid and plate jacks in the center of the con-
trol panel. The red plate jack will be the positive lead.
c. Touch together the two prods and adjust the ohmmeter pointer to zero. Re-
sistance up to 50 megohms can be read directly on the megohm range.
d. Electrolytic capacitors can be checked for leakage. Observe that the red
(plate) jack is connected to the positive pole of the capacitor.
21. NORMAL-LOW Plate Volts. In the NOTATIONS column of the data chart for
some tubes will be found PLATE VOLTS = LOW. This notation indicates that the PLATE
VOL TS
switch located just above the FUNCTION switch is to be set on the LOW position.
Return the switch to NORMAL for all other tubes.
22. Heater - Current. In the lower right hand corner of the panel will be found two
binding
posts which are normally connected together by a jumper. By removing this
jumper and connecting a suitable Milliammeter or Ammeter between these two binding
posts, the indicating instrument will read the current being drawn by the heaters of the
tube under test.
The actual voltage at the tube under test will be the voltage as indicated by the fila-
ment selector switch minus the voltage drop across the indicating Milliammeter or Am-
meter. This voltage will generally be of a very low magnitude, but can be calculated by
mUltiplying the
current normally drawn by the tube under test by the impedance of the
meter connected in series with this tube, or it can be actually measured with a sensitive
AC Voltmeter.
If the impedance of the meter is much more thanO. 2 ohms, the voltage drop might
be appreciable percentage-wise to the voltage delivered to the tube. For example, if the
current at the tube is normally 0.6 amperes, and the impedance of the current measuring
instrument were O. 5 ohms, the resultant loss would be the product of these two, or O. 3 of
one volt.
23.
Pilot Lamp Testing. The center of the large 7-pin socket is used to check pilot
lamps. Set the filament selector switches on HR. Set the filament voltage switch to the
proper voltage for the lamp being tested.
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