Hickok 800 - User Manual

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Calibration Testing of the Hickok Model 800/800A Tube Testers

Version 1.0, September 2006

Use this procedure to test and calibrate the Hickok Model 800/800A mutual conductance (AKA transconductance)

tube testers. Except as noted, all of the readings are taken with a 1000 ohms per volt meter. If an accurate 1000 ohms per

volt meter is not available a modern high impedance analog or digital voltmeter can be used with appropriate shunt

resistors in parallel with the input to simulate proper loading. The following resistor values should be used: 10 volt scale

use 10K, 50 volt scale use 51K, 250 volt scale use 250K. All resistors are 1/2 watt 5% carbon composition.

Calibration will be easier if you supply AC power through a constant voltage regulation type transformer to do the

tests, but this is not essential. Recalibrate the tester any time either rectifier tube is replaced. The correct type #81 fuse lamp

must be installed in the tester or false readings can result. For the identification and location of adjustments and for

troubleshooting refer to the ADJUSTMENT CHART immediately following the test sequence.

It is assumed that the person performing the testing and adjustment is knowledgeable in electronic service and

aware of the dangers in working on equipment using high voltages. Do not attempt to service equipment if you are not

experienced in such work. Serious shock or death could result in improper action or procedure.

PREPARATION

Remove all of the screws around the outside of the panel that hold the tester to the case. Remove the tester from the

case and set it up on spacers so that the front panel is facing up in the normal operating position. Before applying power

adjust the mechanical zero on the meter to set the pointer exactly at the zero line on the scale.

Turn on the tester and allow it to warm up for 5 minutes. Set the tester programming switches to these settings: 6.3

JR-5347-2 0 0. Set the SHORTS switch to the TUBE TEST position. Do not insert any tubes in the test sockets.

LINE ADJUST

1. Push switch P7 and rotate the LINE ADJUST until the meter points directly to the LINE TEST mark in the center of the

meter scale. Release P7.

ENGLISH POSITION

2. Rotate the ENGLISH control fully counter clockwise and verify that the pointer lines up with the 0 mark on the scale.

BIAS POSITION

3. Rotate the BIAS control fully counter clockwise and verify that the pointer lines up with the 0 mark on the scale.

SHORTS TEST

4. Connect a 1 megohm resistor between pins 8 and 1 on the octal socket. Rotate the SHORTS switch to positions 1

through 5 and observe that the meter reads about 1 megohm in all short test positions. Return the SHORTS switch to the

tube test position.

FILAMENT VOLTAGE TEST

5. Connect an AC voltmeter to pins 2 and 7 of the octal socket. While observing the reading on the meter, rotate the

FILAMENT switch from the minimum through the maximum voltage positions and verify that the voltage agrees with the

setting. The readings should be within plus or minus 10% of nominal. Return the FILAMENT switch to the 6.3 volt

position.

PLATE VOLTAGE TEST

6. Connect the negative lead of a DC voltmeter to pin 8 of the octal socket. Connect the positive lead to pin 3. Push the P4

GM button and read the voltage. Normal plate voltage is 150 volts plus or minus 5 volts. Release P4.

SCREEN VOLTAGE TEST

7. Move the positive lead of the DC voltmeter to pin 4 of the octal socket. Push P4 and read the screen voltage. Normal is

130 volts plus or minus 5 volts. Release P4.

REDUCED SCREEN VOLTAGE TEST

8. Hold P4 and press P1. The reading should drop to 56 volts plus or minus 3 volts. Release P1 and P4.

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Summary

Preparation and Initial Setup

Tester Preparation

Remove tester from case, position, and adjust mechanical zero.

Initial Settings

Set warm-up time, programming switches, and SHORTS switch.

Calibration Tests

Fundamental Voltage Tests

Line, Filament, Plate, Screen voltage tests.

Performance Tests

Shorts, Bias, Grid Signal, Balance, Meter, Conductance tests.

Adjustment Chart

Control Adjustments

Adjustments for Line, English, Bias, and voltage controls.

Calibration Adjustments

Adjustments for meter bridge and mutual conductance.

Control Maintenance

Procedures for cleaning and aligning controls.

The Hickok Model 800/800A Tube Tester is a mutual conductance (AKA transconductance) tube tester designed for evaluating the performance of vacuum tubes. This document outlines the calibration and testing procedures, as well as maintenance guidelines, for the device.

Function Description:

The primary function of the Hickok Model 800/800A is to measure the mutual conductance of vacuum tubes, which is a key indicator of a tube's ability to amplify a signal. It also performs various other tests including shorts, filament voltage, plate voltage, screen voltage, reduced screen voltage, grid bias voltage, grid signal voltage, plate and screen supply balance, meter bridge balance, diode/rectifier tests, and gas tests. The tester is designed to help discern good tubes from bad ones for service work, rather than providing absolute quality measurements.

Important Technical Specifications:

Meter Type: Requires a 1000 ohms per volt meter for most readings. If not available, a high impedance analog or digital voltmeter can be used with shunt resistors: 10K for 10V scale, 51K for 50V scale, 250K for 250V scale (all 1/2 watt 5% carbon composition).
Plate Voltage (Normal): 150 volts ± 5 volts DC.
Screen Voltage (Normal): 130 volts ± 5 volts DC.
Reduced Screen Voltage: 56 volts ± 3 volts DC (when P4 and P1 are pushed).
Maximum Grid Bias Voltage: -39 volts ± 1 volt DC.
Grid Bias Voltage (Set to 22): -3 volts ± 0.2 volt DC.
AC Grid Signal Voltage: 2.5 volts AC ± 0.125 volts (some earlier testers used 5.0 volts AC).
Mutual Conductance Reading (Calibration): 2000 micromhos ± one small division on the 3000 scale.
Meter Movement: Nominal full scale current of 500 microamps, movement resistance of 233 ohms (values may vary with production changes).
Fuse Lamp: Requires a correct type #81 fuse lamp for accurate readings.

Usage Features:

Preparation: Before use, remove the tester from its case, set it on spacers with the front panel up, and adjust the meter's mechanical zero. Allow 5 minutes for warm-up.
Programming Switches: Set to 6.3 JR-5347-2 0 0 for initial setup.
Shorts Test: Rotate the SHORTS switch through positions 1-5, expecting a 1 megohm reading.
Line Adjust: Push P7 and rotate LINE ADJUST until the meter points to the LINE TEST mark.
English/Bias Controls: These controls are used for setting measurement ranges and tube operating points. They should be rotated fully counter-clockwise to verify zero readings.
Push Buttons: P1 (DIODE), P2 (0Z4), P3 (RECTIFIER), P4 (GM), P5 (GAS 1), P6 (GAS 2) are used to initiate specific tests.
Filament Switch: Used to select various filament voltages.
External Voltage Source: For mutual conductance calibration, an isolated current-limited AC voltage source (e.g., variable transformer + isolation transformer) is required, adjustable to 50.0 volts AC.
Oscilloscope: A DC coupled oscilloscope is used for plate and screen supply balance tests to observe 120Hz pulsating DC peaks.

Maintenance Features:

Recalibration: The tester should be recalibrated any time either rectifier tube is replaced.
Adjustment Chart: A detailed chart is provided for identifying and locating adjustments, and for troubleshooting.
LINE ADJUST Calibration: For later 800A versions with an R24/100K adjustable resistor, R24 is adjusted to align the meter to the LINE TEST mark after setting plate voltage to 150V. For earlier versions, the 215K fixed resistor in the AC line voltage metering circuit should be checked.
Meter Movement Adjustment: A factory-applied magnetic shunt (metal plate on the side of the meter) can be adjusted by loosening its screw and sliding it to fine-tune full-scale deflection. However, this affects mutual conductance readings and should be a last resort.
ENGLISH/BIAS Control Alignment: Knobs can be repositioned by loosening set screws.
Reduced Screen/Grid Bias Voltage Adjustment: This involves adjusting two sliding taps on resistor R15 (8.5K). The grid bias voltage should be set first, then the reduced screen voltage, repeating as necessary due to interaction.
Control Cleaning (ENGLISH Control): If the ENGLISH control is dirty or intermittent, it's recommended to remove and clean both sections. This involves disassembling the control (removing retaining rings, unsoldering connections) and cleaning contacts with an ultrasonic cleaner, detergent solution, water rinse, and isopropyl alcohol, followed by air drying. Reassembly is done without reapplying solder to allow for alignment.
Control Alignment (MUTUAL CONDUCTANCE CALIBRATION): After cleaning, the ENGLISH control needs alignment. This involves loosening the solder spot on the shell of the back resistor section to allow rotation. With the control temporarily connected to the tester, set the knob to the orange dot (near 73), push P4, and rotate the shell of the front section until the meter reads 2000 on the 3000 scale. Once aligned, secure the shell with tape and then re-solder.
Rectifier Tube Replacement: If plate or screen supply balance is incorrect, the 83 or 5Y3 rectifier tubes should be replaced.
Fuse Lamp Check: A burned-out bias fuse lamp can cause low bias or grid signal voltage.
Resistor Checks: For diode/rectifier tests, resistors R4 (12 ohms), R5 (1.2K), R6 (1.8K), R22 (200 ohms) should be checked if readings are incorrect. For gas tests, R17 (180K) should be checked.

Important Notes:

Working on the tester involves high voltages; only experienced personnel should attempt service.
The tester's calibration constants are dependent on original components and conditions. Replacing vacuum tube rectifiers with solid-state devices or making other circuit modifications can compromise accuracy.
Hickok compensated for minor variations in operating voltages and component tolerances by adjusting roll chart numbers, making the testers suitable for their intended purpose of distinguishing good from bad tubes for service work.
Component designation numbers refer to the Hickok schematic diagram for the 800A model. Variations between units are expected due to manufacturing changes over time.