Hickok 600A Manual - Página 6

Procurar online ou descarregar pdf Manual para Equipamento de teste Hickok 600A. Hickok 600A 6 páginas. Tube testers

rotating. Perform the test once more and verify that the knob didn't move and the shell didn't slip before it was secured

with the tape. Reapply just a little solder spot to the shell to permanently secure the shell in place and re-install the control

in the tester. After reassembly do a final re-test. Be careful when you do this adjustment because of the dangerous voltages

in close proximity. Wear insulated gloves and understand exactly what you are going to do before you start.

15. DIODE/RECTIFIER TESTS: The diode and rectifier tests assess the voltage drop across the rectifier by applying a

fixed voltage with a series limiting resistor and measuring the available plate current. If the readings are not correct for any

of the P1, P2 or P3 tests check resistors R9 / 12 ohms, R2 / 1.2K, R1 / 1.8K, R16 / 200 ohms. The sensitivity of the meter

and the accuracy of the ENGLISH control also affect this test.

16. GAS TEST: The gas testing circuits depend on the meter bridge, ENGLISH and BIAS controls. If the mutual

conductance tests are functioning properly, check for bad switches or dirty contacts on P5 and P6. Also check R8 / 180K

resistor. This resistor is placed in series with the grid for the gas test when P6 is pressed. Any grid current due to gas will

cause a voltage drop across R8. The plate current goes up as the grid bias drops indicating gas in the tube.

NOTES

Always test the two rectifier tubes first if trouble is suspected. Check for out of tolerance resistors, inaccurate meter

movements, dirty switch contacts, dirty ENGLISH control or a bad transformer. The type of measuring instruments used or

other factors not related to the tester itself can give readings that appear to be a little out of specification. Some of the

important factors are the DC operating voltages, power supply balance and the AC grid signal voltage.

The mutual conductance measurement circuit assumes a correct AC grid signal voltage. If the AC grid signal

voltage is wrong, the displayed mutual conductance reading will be wrong by the same amount of error even though the

DC voltages and mutual conductance measurement circuit are calibrated correctly. Hickok did not provide a means for

adjusting or regulating this voltage, relying on the transformer winding to be pretty close to the right value. The AC signal

voltage will change depending on things like the setting of the bias control, heater load and plate current but, for the

purpose the tester was intended, this is good enough. Hickok knew these things and compensated the roll chart numbers to

provide adequate test results. The cutoff point where a tube is judged good or bad is rather arbitrary and subjective

depending on the application so some error is not all that important. Hickok testers are not designed to measure the

absolute quality of a tube but to discern the probable good from the probable bad in connection with service work.

There are several points to consider on the replacement of the vacuum tube rectifiers with solid state devices or

other design changes. Hickok made a lot of assumptions and clever design tradeoffs to manufacture an instrument that

worked well but was not overly complicated or expensive. Calibration constants of the tester are very much dependent on

certain conditions remaining in place such as voltage drops due to the rectifier heater current consumption and the effect of

plate resistance voltage drops in the rectifiers. Any circuit modifications including substitution of the rectifiers with

anything but the original types will compromise the accuracy and should be avoided.

The component designation numbers given refer to the parts listed in the Hickok schematic diagram included with

the operators manual for the model 600A. Hickok revised and changed the 600 and 600A several times during the

manufacturing life of the instrument. Some deviation is to be expected from unit to unit depending on the year of

manufacture. These calibration guidelines serve as a model for a general outline on calibration. Individual testers may vary

as to the physical layout or other details. All of the Hickok mutual conductance testers use the same basic circuit with small

variations. Many of the other models, especially the small service type testers can be checked using the same voltage

specifications. Significant variations in the AC grid signal voltage might be found in earlier testers. Earlier testers used 5.0

volts AC rather than the 2.5 volts used later. Other model testers used a selection of AC grid signal voltages depending on

the meter range selected.

Hickok is a registered trademark of the Hickok Electrical Instrument Company, Cleveland Ohio.