Although no longer standard equipment for industrial electronics, vacuum tubes were incredibly important to the rise of electronic devices in the earlier parts of the 20th century for their ability to convert an alternating current into a direct current. Vacuum tubes are still used today, mainly by hobbyists. The Avo CT-160 is a vacuum tube testing device manufactured in the 1950s, but remains one of the easiest-to-use and most thorough testing devices for vacuum tubes available. A full range of continuity, current and mutual conductance tests can be conducted using the Avo CT-160 on any vacuum tube.
- Skill level:
- Moderately Easy
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Things you need
- Vacuum tube
- Avo CT-160
- Tube manual
Take your vacuum tube and plug it into the appropriate socket in the top half of the Avo CT-160 tube tester. The bottom side that plugs in is the side with protruding filament pins. There are 20 different tube sockets located inside the Ave CT-160 accommodating tubes containing anywhere from four to nine filament pins. Find the sockets containing the appropriate amount of filament pin openings, and insert your vacuum tube into the socket that best fits your tube. Do not attempt to force the tube into a socket.
Read your vacuum tube's manual to find voltage, current and other specifications for your vacuum tube. You will need this information to properly set the switches on your Avo CT-160. If you do not own a tube manual for your vacuum tube, you can find it using the tube manual database found at scottbecker.net/tube/index.html. Have your vacuum tube's model number on hand, which will be printed on the vacuum tube's glass.
Turn the pinout thumbwheel switches to match the pinouts of your vacuum tube as laid out in the diagram from your tube manual. For the abbreviations on the thumbwheel indicator, 'A' refers to 'anode,' 'C' refers to 'cathode,' 'G' refers to 'grid' and 'H' refers to 'heater.' For internal connections, or pinouts that are extra because there are less than nine filament pins, turn the switch to 'O.' The thumbwheel indicator will display a number and a letter; just worry about the letter.
Set your Avo CT-160's switches to correspond to the data from your tube manual. The 'Circuit Selector' switch, found on the bottom-right of the Avo CT-160, should be turned to the 'Set~' position. Set the 'Heater Volts,' 'Neg. Grid Volts,' 'Anode Volts' and 'Screen Volts' switches to correspond to the proper voltage levels found in the manual. These switches are on the left side of the Avo CT-160's bottom half. Set the two dials labelled 'Anode Current' to reflect the current of the anode in milliamps. These dials are found above the 'Circuit Selector' dial. The left 'Anode Current' dial is for single digits, and the right is for double digits. For example, if the tube manual stated that your vacuum tube conducted 48 milliamps through the anode during operation, turn the left 'Anode Current' dial to 8 and turn the right dial to 40.
Turn on the power to your Avo CT-160. The main power supply switch, labelled 'Mains,' can be found below the 'Heater Volts' dial.
Turn the 'Circuit Selector' switch to the 'H/Cont' position. This begins a test of the heater continuity for your vacuum tube. Observe the position of the indicator on the main display meter, which is found just above the Avo logo on the CT-160's bottom half. The indicator will be utilising the bottom strip on the meter to report the continuity measurement. If the indicator goes all the way to the zero position to the left of the meter, the vacuum tube is not working properly and should be replaced.
Turn the 'Circuit Selector' switch to the 'Test' position. This will begin a test of the vacuum tube's anode current. Dispose of your vacuum tube if the Avo CT-160's buzzer sounds; this denotes that the vacuum tube contains faulty parts that are impeding the electrical current. The vacuum tube should also be disposed of if it lights up during the test, as this means that gas has leaked into the glass vacuum tube. The indicator on the main display meter should be pointing directly up at the zero position on the top strip. If this is not the case, raise or lower the 'Anode Current' dials accordingly. When the indicator is pointing straight up, the 'Anode Current' dials will be reading the actual current passing through the vacuum tube.
Refer to your vacuum tube's manual for the proper mutual conductance measurement, and rotate the 'Set ma/V' dial until that dial's indicator points to the appropriate measurement. This will allow you to test the vacuum tube's mutual conductance, or ability to transmit an electrical signal through the tube. This test uses the middle strip on the main display meter. If the indicator points toward the red area on the left of the strip, labelled 'Replace,' your vacuum tube should be replaced. If the indicator points toward the yellow-green area on the strip's right, labelled 'Good,' or the nameless white section in the middle, your vacuum tube is still usable.
Turn the 'Circuit Selector' back to the position labelled 'Set~.' Switch the main power supply off. Give your vacuum tube about five to ten minutes to cool off properly before attempting to remove it from the Avo CT-160.
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