ページを印刷するGRID BIAS VOLTAGE
9. Remove the type 49 bias fuse lamp and verify that it is of the correct type and it is good. Put a good type 49 lamp back
into the tester. Connect the negative lead of a high impedance DC voltmeter to pin 8. Connect the positive lead to pin 5. Do
not use a compensating shunt resistor for this test. Adjust the BIAS control fully clockwise. Verify that the maximum
voltage is -39 volts plus or minus 1 volt. Set the BIAS control to 22. Verify that the reading is -3 volts plus or minus .2 volt.
GRID SIGNAL VOLTAGE TEST
10. Set the BIAS control to zero. Connect a high impedance AC voltmeter to pins 8 and 5 and measure the grid signal
voltage. Do not use a compensating shunt resistor for this test. The AC grid signal voltage should be 2.5 volts AC plus or
minus .125 volts.
PLATE SUPPLY BALANCE TEST
11. Connect a DC coupled oscilloscope to pin 3 of the octal socket. Use pin 8 as a common for the scope. Press P4.
Observe the plate voltage and obtain a display on the scope that shows the rounded peaks of the 120Hz pulsating DC with
as high a gain as possible. Set the vertical position on the scope to move the trace downward as you adjust the gain upward
to maintain the top of the trace on the screen. Verify that the alternating peaks of 120Hz DC are of equal amplitude.
Release P4.
SCREEN SUPPLY BALANCE TEST
12. Remove AC power from the tester. Connect the scope probe ground lead to pin N, the center tap of the power
transformer winding for the 5Y3 plates. Connect the scope probe to pin K, the center tap of the power transformer winding
for the 5Y3 rectifier filament and reapply AC power. Adjust the scope as before to display the 120Hz peaks, and observe
the screen bias voltage. Verify that the alternating peaks of 120Hz DC are of equal amplitude. Remove AC power and
disconnect the scope. Reapply AC power for the next test.
METER BRIDGE BALANCE
13. Connect a 10K 10 watt 1% resistor between pins 3 and 8 of the octal socket. Set the ENGLISH control to zero then
rotate it clockwise to the orange dot near number 73, which is the 3000 micromho scale setting. Press P4 and observe the
meter reading. Verify that the meter reads zero or no more than one small division high or low. Rotate the control from end
to end to see if the balance changes positive and/or negative with control rotation. Release P4 and remove the resistor.
MUTUAL CONDUCTANCE READING TEST
14. Verify that the panel switches are set up to the conditions as given in PREPARATION at the beginning of this section,
(JR 5347-2) FILAMENT at 6.3 volts. Set the BIAS and the ENGLISH controls to zero. Rotate the ENGLISH control
clockwise to the orange dot near number 73.
For the following mutual conductance test you will need to set up an isolated current limited source of AC voltage.
Use the setup drawing in figure 1 to connect the equipment to the tester. Be careful because improper connection can cause
serious damage. Connect the source to pins 8 and 3 of the octal socket. If the main meter deflects downward instead of up
when you perform the test, swap the connections to pins 8 and 3. Measure the voltage source directly across the secondary
of the isolation transformer. Do not use a shunt resistor across the meter.
Push P4 and slowly adjust the voltage source up to exactly 50.0 volts. Observe the reading on the tester meter. The
correct reading is 2000 micromhos plus or minus one small division on the 3000 scale. It may be slightly worse depending
on the quality of the ENGLISH control. After taking the reading set the voltage back to zero and release P4.
DIODE/RECTIFIER TESTS:
FIGURE 1