The plate current can also be measured using the "shunt" approach, where an ammeter is paralleled across each side of the output transformer.This method is practical, but can also be dangerous because of the high voltages on the plate. If a 1 ohm resistor is used, the plate current in milliamps is equal to the voltage across the resistor in millivolts (50mV across the 1 ohm resistor indicates 50mA plate current). The actual plate current can then be measured as the voltage drop across this resistor. The plate current can also be measured by permanently installing a resistor in the plate lead of each output tube. It has socket adapters and direct reading meters, so the user doesn't come in contact with the high voltages, and the socket adapters are on the other side of the chassis, so the wiring is somewhat isolated from the rest of the circuitry to help prevent oscillations. However, there is a commercially available device that uses this principle, the Allessandro Bias Meter.
It can also cause error-inducing or potentially damaging oscillations if the meter leads get close to other parts of the circuitry.
This method is not very practical because it requires desoldering the plate connections, and is dangerous due to the high voltages involved, and should be avoided. The plate current can be measured by inserting a DC ammeter in series with each plate lead, which allows a direct reading of the plate current.
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