Hickok 539C - Tube Testing Procedures; Operating Leakage Test Procedure; Gas Content Testing; Dynamic Transconductance Testing

engineer and technician will find this feature a great aid in routine investigations.
Every engineer knows that in certain tube applications, leakage is more significant
than in others. The metered leakage feature of the Model 539C will enable him to
form sound judgment as to the leakage to be tolerated in different applications.
7a. Operating Leakage Test: Thrning the SHORTS switch through positions A, B, C, D,
E isolates tube elements successively from all other elements and registers the
leakage in megohms between the chosen element and all others connected in parallel.
Forty volts d. c. is applied in this test. The significance of the lettered positions of
the short switch is as follows:
* A - HEATER isolated from other elements.
B - GRID isolated from other elements.
C - SCREEN isolated from other elements.
D - PLATE isolated from other elements.
E - SUPPRESSOR isolated from other elements.
* NOTE: Position A includes heater-cathode leakage. In tubes having filamentary
cathodes, the heater and cathode are identical; therefore the meter will normally
indicate near the zero mark on position A of the shorts switch.
8.
Gas Test: The push switches P5 (Gas l)and P6 (Gas 2) are used to test amplifier tubes
for gas content.
9.
a. Make Micromho test in the ordinary way.
b.
Set the Bias Voltmeter switch to the 50 volt range and the Function switch to posi-
tion D. Hold down P5 and adjust the Bias control to bring the meter reading down
to
500 on the 3000 scale.
c. Hold down P5 and press P6. Because of a charging capacitor the meter will de-
flect either up scale or down scale about one division, after P6 is pressed, and
will settle 'to a new reading. An upscale reading after settling is the result of
grid current due to gas or grid emission (sometimes referred to as pOisoned grid).
If the upward movement is not more than Qne large division (two small divisions),
the gas content is satisfactory.
Some tubes develop gas after being heater for a period of time. If a tube is sus-
pected, allow it to heat for. a few minutes. This constitutes a very sensitive gas
test. Gas content on the order of O. 1 microampere can be detected.
Gas content is a very important factor in modern receivers of all types, con-
taining A VC and AFC circuits as the presence of gas causes the grid to become
conductive and as changes in grid bias operate through resistors of comparatively
high value, correct functioning cannot be obtained with a gassy tube. The presence
of gas results in actually changing the grid bias. Gas is especially harmful in
television tubes.
Dynamic Transconductance: The Push Switch P4 is mechanically divided into two sec-
tions, non-locking and locking. Both sections perform identical electrical functions.
If momentary contact is needed, press the non -locking button. If extensive tests are
to be made, use the locking button. The locking button is released by preSSing the
non-locking button.
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