Hickok 800A Calibrazione - Pagina 4
Sfoglia online o scarica il pdf Calibrazione per Apparecchiature di prova Hickok 800A. Hickok 800A 6. Tube testers
Stampa la pagina5. FILAMENT VOLTAGE TEST: No adjustment. This voltage is entirely dependent on the power transformer and the AC
line setting. See also ADJUSTMENT CHART 1, LINE ADJUST above. Some voltages may be slightly higher due to the
transformer having no load.
6. PLATE VOLTAGE TEST: No adjustment. This voltage is entirely dependent on the power transformer and the AC line
setting. See also ADJUSTMENT CHART 1, LINE ADJUST above. If the AC line test circuit is reading correctly, check
and/or replace the type 83 rectifier tube.
7. SCREEN VOLTAGE TEST: No adjustment. This voltage is entirely dependent on the power transformer and the AC
line setting. See also ADJUSTMENT CHART 1, LINE ADJUST above. If the AC line test circuit is reading correctly,
check and/or replace the type 5Y3 rectifier tube.
8. REDUCED SCREEN AND GRID BIAS VOLTAGE ADJUSTMENTS: The 56 volt reduced (P4 and P1 pushed) screen
grid voltage measured in step 8 and the –39 volt control grid bias voltage measured in step 9 is set by adjustment of the two
taps on R15 / 8.5K. If adjustments are necessary to either the reduced screen voltage or the grid bias voltage, adjust the
control grid voltage first because that affects the reduced screen grid voltage also. Before doing any adjustments always
verify that the screen supply voltage is 130 volts. Adjust the AC line control until it is.
In both versions of the 800/800A the grid bias is controlled by the series combination of R15 a tapped power
resistor, and R16 the front panel BIAS adjust control. Remove the tester from the case and prop it up on a work surface
face down such that you can reach and push the control panel buttons P4 and P1. Set it up with the top edge of the control
panel facing you and the panel meter to the right.
To set the grid bias voltage, adjust the BIAS control fully clockwise. Loosen the clamp screw of the sliding tap on
resistor R15. This is the tap with the jumper wire to the end tab on R15. Gently hold the tap with insulated pliers and slide
the tap until the voltage is as close to –39 volts as you can get it. Tighten the screw to secure the tap in place. Don't over
tighten the screw. Only enough pressure to keep the tap from sliding is sufficient.
To set the reduced screen voltage perform test 8. Loosen the clamp screw of the second sliding tap on resistor R15.
This is the tap that is not connected to the end tab of R16. Gently hold the tap with insulated pliers and slide the tap until
the voltage is as close to 56 volts as you can get it. Tighten the screw to secure the tap in place.
There is some interaction between the two adjustments so repeat tests 8 and 9 and adjust as necessary to get both
voltages within the limits.
9. GRID BIAS VOLTAGE: See step 8 above. A burned out bias fuse lamp will cause the bias voltage to be low.
10. GRID SIGNAL VOLTAGE TEST: No adjustment is possible for this voltage. The voltage is entirely dependent on the
power transformer and the AC line setting. Make sure that the AC line setting is correct and that the AC line set function is
working properly. A burned out bias voltage fuse lamp can cause the grid signal to be low.
11. PLATE SUPPLY BALANCE TEST: This is entirely dependent on the power transformer and the rectifier tubes. If
balance is incorrect replace the 83 tube.
12. SCREEN SUPPLY BALANCE TEST: This is entirely dependent on the power transformer and the rectifier tubes. If
balance is incorrect replace the 5Y3 tube.
13. METER BRIDGE BALANCE: The meter bridge balance is determined by the relative positions of the upper and lower
halves of the ENGLISH control. The ENGLISH control is designed so that the two halves form the two legs of a balanced
bridge circuit. As the control is turned clockwise the two halves decrease in resistance by the same amount thereby
decreasing the sensitivity of the bridge so that higher transconductance readings are displayed without over scaling the
meter. The resistance of both halves of the control must track each other as they are rotated or the bridge will become
unbalanced, adding or subtracting a constant number from the correct reading. If the power supply is properly balanced and
the meter does not read zero or close to it with this test, the ENGLISH control is not balanced. If the control becomes dirty
and intermittent the resistance will change abruptly and deviate from normal as it is rotated causing the zero to fluctuate or
jump adding error. Because these are not high precision controls some fluctuation is always going to be seen as they are
moved through the full span of rotation, especially at the end points and sometimes when the direction of rotation is
changed. If the total fluctuation is on the order of four or more small divisions on the meter and cleaning doesn't help, the
only solution is to replace the control. To clean a dirty control, follow the Control Cleaning instructions given below.