Fixer-Uppers will cost more to fix than buying a good one. The model is somewhat similar to but really demands a premium price, and can be touchy to keep running. Hi Tom, Are they easy to calibrate to be able to test some tubes? Do you already have an account? The A does not have this. About equal to a 25 watt bulb.
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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 Observe the reading on the tester meter.
The correct reading is micromhos plus or minus one small division on the scale. After taking the reading set the voltage back to zero and release P4. Connect the cathode of the rectifier to pin 8 of the octal socket. Connect the other lead of the resistor to pin 3 of the octal socket.
Release P1. Adjust the control to GOOD scale is read for the test results. Release P3. Press the P2 0Z4 test button. Release P2. Obtain a 6L6 tube that is known to be free of gas. Put the tube in the tester and set it up for the standard 6L6 test. Adjust the BIAS control for a reading of on the scale. Release P6 and P5. Connect a 1Meg resistor between pin 5 and pin 7 of the nine pin miniature socket.
Repeat the test. This time verify that the reading goes up by 4 to 5 small divisions on the meter when the P6 button is pushed. This completes the testing and calibration procedure. The volt plate supply is used as the reference when setting the AC line voltage adjustment. The AC line control is adjusted until the plate voltage is volts as read on the meter. All of the other operating voltages follow along and are assumed to be correct.
If the plate supply is abnormally high or low then adjusting it to the nominal volts with the line test will cause all of the other operating voltages to be shifted. This is because the line adjust will be compensating for an abnormal plate supply and also affecting every other operating voltage.
If the plate supply voltage is normal and all of the other voltages are wrong by the same percentage, look at the plate supply for problems. If the AC line test circuit itself is bad the plate and other voltages will all be wrong. If the plate and other voltages are not correct after setting the AC line adjustment, check the resistors in the AC voltage metering circuit R24 and R Also check the meter movement and verify that it indicates full scale when passing the nominal full scale current.
Older testers used a 1. Later versions were microamps and ohms of resistance. Other values may have been used as production changes were made through the years. The metal plate mounted on the side of the meter is a factory applied magnetic shunt. By loosening the mounting screw and sliding the plate back and forth, small adjustments can be made to the full scale deflection of the meter.
Bear in mind though that changing the meter adjustment will effect the mutual conductance reading too so rule out everything else before adjusting the meter. Loosen the set screw on the knob and reposition the knob to the correct location.
Retighten the set screw. R28 sets the shorts test sensitivity. If adjustment is necessary set R28 fully counterclockwise and slowly rotate it clockwise until the short lamp just begins to glow. No adjustment. This voltage is entirely dependent on the power transformer and the AC line setting. Some voltages may be slightly higher due to the transformer having no load.
Earlier versions of the do not have the provision to reduce the screen voltage. Pressing P1 will have no effect on the screen voltage. For later versions 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 R6.
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 volts. Adjust the AC line control until it is. 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 R6. This is the tap with the jumper wire to the end tab on R6. 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. Only enough pressure to keep the tap from sliding is sufficient. On later versions to set the reduced screen voltage perform Test 8.
Loosen the clamp screw of the second sliding tap on resistor R6. This is the tap that is not connected to the end tab of R6. 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. There is some interaction between the two adjustments so repeat Tests 8 and 9 and adjust as necessary to get both voltages within their limits. See Step 8 above. 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. This is entirely dependent on the power transformer and the rectifier tubes.
If balance is incorrect replace the 83 tube. If balance is incorrect replace the 5Y3 tube. 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. To clean a dirty control, follow the Control Cleaning instructions given below. If you are not experienced in taking apart controls do not use this as a learning opportunity. It is fairly easy to ruin one and there are no replacements other than salvage from a junk tester.
Set the control to the center of rotation before working on it. Do not rotate the shaft more than a short distance while the halves are separated. On older controls that do not completely separate, if you rotate past the stop you can drop the front wiper into the slot between the ends of the element and it will be difficult to get back out. The back cover is press-fit onto the end of the back section shell and can be removed by prying it off. On the older controls you cannot completely separate the front section from the back.
To separate them enough for cleaning, remove the retaining ring around the shaft where it enters the front section then melt the solder spot and gently pull the shell apart only far enough to keep the solder from holding the two halves together when it cools and no farther. Once the shell sections are separated remove the solder from the surfaces.
Gently separate the front section shell from the cover just enough to provide an opening to infuse an appropriate cleaning solution. A couple of toothpicks placed in the gap will hold the halves separated for cleaning.
Never attempt to pull them farther apart as this will bend and destroy the front section wiper components. On newer controls the front section comes completely apart by removing the retaining ring from the shaft and sliding the shaft out the back of the shell after it has been separated.
The wiper and center tab can be removed and cleaned. The back section cannot be disassembled as the front section but there is enough exposed to do a cleaning. The main problem is not the wirewound element or the slider on the wiper but the sliding contact between the wiper and the center lug of the control. Old dried out grease, dust and tarnish on the contacts that connect the center tab to the wiper are the main problems.
A good cleaning method is to immerse the control in an ultrasonic cleaner for a few minutes using a detergent solution in water.
HICKOK 600A PDF
Calibration and Testing of the Hickok Model 600/600A Tube Testers