How to Choose the Right Tube Checker for Tube Testing?

Posted on Nov 24, 2020

Tube checker

A tube checker, more commonly known as the tube tester, is an electronic instrument designed to test certain characteristics of vacuum tubes (thermionic valves). Digital Tube checkers have evolved along with the vacuum tube to satisfy the demands of the time, and their evolution ended with the tube era.

About Tube Checker

During tube testing, tester tubes are used as a low power rectifier, with all elements other than filament connections connected together as the anode, at a fraction of its normal emission. They are often referred to as the Emission Tester by mistake because they are a crude measure of emission in directly heated types (but a measure of unwanted heater-cathode leakage in indirectly heated types). Switches will need to select the correct filament voltage and pins.


Application – Tube Testing

Tube testing with a tube tester is essential for the measurement of vacuum tubes for various electronic characteristics, such as transconductance, gain, noise, Emissions, and so on.

The Tubes can be graded based on this information to enhance the operation or quality of a vacuum tube audio system. The selection of tubes into sets of similar measurement is called tube matching.

Tube testers are designed as a tool for repairmen to detect tubes that could be causing a problem in the item that the technician was repairing, and the digital tube testers do a very decent job in this role.

However, many people tend not to use a tube tester properly, do not interpret the results correctly, or have unrealistic expectations of them. Other people have developed poor workflow habits that need to be improved. Every tube tester has different capabilities and therefore different operating instructions.


Factors to Consider When Choosing the Right Tube Checker

There are quite many things you need to consider before selecting a tube tester:

  • Make sure you know the intended measurement method and type, including the direct Gm, arbitrary merit value, percentage quality, methods, as well as the design type including AC, DC, AC/DC voltages on Tube Under Test.
  • Make sure you consider the operating voltages that will be available on the tube tester, as well as how many different plate voltage steps are available based on your needs.
  • Determine whether you want a short test method to be available on your desired tube testers.
  • Make sure you consider whether a leakage test is available for your tube tester, and what test method it uses.
  • Consider the factors pertaining to gas test circuit and the accuracy for your tube tester.
  • Consider the noise test feature for your desired tube testers and the related methods used.
  • Consider the availability of a life test (also called the cathode activation test) for your tube tester, as well as the related methods used.
  • Make sure tube sockets are available on the tube testers because they will be needed for plugging in the vacuum tubes (electronic valves).
  • Consider the measurement ranges available for your tube tester as to how many Gm ranges are used, or Good/Bad only or Gm with Good/Bad as well.
  • Make sure you know the test signal frequency and the signal levels used on the desired tube tester.
  • Consider the number of power transformers that are used in the desired tube testers. Normally, it could be one, two or more.
  • Consider how the bias voltage of your desired tube tester is set and monitored. And is it done with a simple dial or with a volt meter?
  • Take the effect of the AC line sag on the test results and accuracy into consideration as well for your desired tube tester.
  • Determine how you want the AC line voltage to bet set and monitored for your desired tube testers.
  • Determine whether you want your tube tester to be tube operated or solid state operated. This is largely associated with calibration timing issue.
  • Determine whether your tube tester is intended for simple use or more complicated and intricate use.
  • Pay attention to the accuracy requirements (e.g. +/- 10 to 15% for less accurate models/versions)
  • Determine how big you want your tube tester to be physically as they can vary in sizes.

With the basics covered, now you have to consider the tubes you plan to test, what level of testing is required and the needed level of test accuracy intended.

The tube tester can do a good job testing your intended tubes based on the tube sockets, operating voltages and test data available. But it ultimately comes down to features, functionality, accuracy, repeatability and your budget.


Final Words

Tube testers have greatly improved in design and capability over the years. But other than laboratory models, most tube testers were service testers and most all service testers, which means they test tube at operating voltages below tube specification data sheet values, but the operating values chosen were proportionally close in test result value to the stated data sheet values so they were valid.

Despite the development, all tube testers are required to undergo maintenance and calibration every now and then. If not completed, the accuracy and trust in the test results will be rendered useless. Tube testers are unlike radios where you buy them, take them home and they eventually stop working.

So, be prepared to spend some on repair and calibration on any tube tester you buy unless it is sold as repaired and calibrated. What features and their specifications will depend on your needs and expectations in the final accuracy of the test results.


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