The Maxi-Preamp measures Gain, Transconductance, and Noise (dB) in signal tubes. It has LED indicators on the front panel showing whether a tube under test is operating or not, and then also displays on the LCD screen an exact measurement of the currently selected test function. If the LED is lit red instead of green, this indicates a failure or shorted tube.
The Maxi-Preamp does not have an emission test – this is often a dangerous test to make on a tube, depending on how it is done, and we don’t feel it has that much value.
The best test you can make of a tube is for Transconductance, which is a measure of how well the tube amplifies signal, how strong it is and/or gassy it might be. The higher the number, the stronger a tube is generally.
You may measure Gain (multiplication factor) correctly, and it may have low noise, but the tube is not very strong, which is what Transconductance is. This is why we suggest measuring for this factor, as it is a dynamic measurement which mimics the way a tube is actually used in amplifier.