Guitar Amp Tools
Definitions of Test Parameters
The Voltages and currents of the Amplifier and the measured parameters of the tube in the amplifier are displayed at once and in real-time. This allows the user to view the changes made while adjusting the Bias to determine the Dissipation of the vacuum tube
Mutual Conductance (or Transconductance) is a measurement of how well a signal into the tube can control the current moving thru the tube. Over time a signal into the tube doesn’t change current moving thru it. It has lost it’s power as an amplifier and therefore it is the best indicator of the quality of the tube.
Gain is the ratio of the signal in vs. the signal out. A 12AX7 has a published gain of 100, i.e 1 volt signal in can give you 100 volts out. This is highly dependent on the circuit, the theoretic gain of 100 is the maximum the tube could produce. It is a ratio of input to output therefore it has no units
The Plate Voltage is the high voltage supplied by the amplifier. It is somewhere in the 400 Volt to 600 Volt range, so it is potentially lethal. The capacitors in the amp can stay charged even after the amplifier is unplugged
The Plate current is a measure of the electrons flowing from the cathode to the high voltage Plate. With antique tube testers this was called emissions; literally measuring the current flowing from the cathode to the plate
The Plate current is a measure of the electrons flowing from the cathode to the high voltage Plate. With antique tube testers this was called emissions; literally measuring the current flowing from the cathode to the plate
The Plate Voltage is the high voltage of the amp. It is not adjustable, it is in the design of the manufacturer of the amplifier. If the plate voltage is not in the hundreds of volts it is usually a blown fuse, which may be located inside the amp. This may also be an indication of a bad output transformer or high voltage winding of the power transformer
The Plate current is a measure of the electrons flowing from the cathode to the high voltage Plate. With antique tube testers this was called emissions; literally measuring the current flowing from the cathode to the plate
The Bias is the negative voltage placed on the the control grid of the tube. The negative voltage chokes off the current flowing thru the tube to some extent. A signal is then placed onto the Bias, manipulating the current through the into an amplified version of the original signal. It may or may not be adjustable, according the the design of the amp
The Dissipation of the tube is a measure of the wattage flowing through the tube and is dictated by the Bias Voltage. The more negative the Bias, the lower the dissipation will become. This is determined by the design of the amplifier and if possible, contact the manufacturer of the amp.