| All the tubes we sell are tested prior to shipping, even though the suppliers test them, we retest them again. We do this by using a B & K DYNA-QUIK Model 707. This Model 707 measures Dynamic Mutual Conductance. This insures that the tube will perform as specified.
In guitar amp circuits practically all tubes (except rectifiers and diodes) are used as some type of amplifier. Even oscillator circuits are basically amplifiers with regenerative feedback. Therefore, the most important characteristic to be checked to determine how effectively any tube will function in its circuit, is its ability to amplify. This, in turn, is governed by its mutual conductance.
All Tubes have to pass the following 3 tests:
- Grid Emission and Vacuum Test: Each tube is checked for grid to cathode emissions, contaminated grids, or lack of vacuum. In other words, NO Shorts.
- Quality Test: This test is made only if the tube passes the NO shorts test above. This test measures the mutual conductance. Measuring the mutual conductance of a tube provides the most accurate and all inclusive single test that can be made on any tube.The tube must meet or exceed the manufacturers specifications for that type of tube.
- Life Test: This measures the amount of useful life still remaining in the tube. We do this test by reducing the heater or filament voltage to a predetermined amount. If the quality or mutual conductance remains high, the tube being tested has 90-95% of its useful life remaining.
© 1998 Zack@vibroworld.com
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