Connect the DC voltage regulator to the two "Input" terminals of the 6V6 bias amp.
Set the measurement on the voltmeter to 20V. Place the voltmeter's black probe on one side of the 6V6 resistor and the voltmeter's red probe on the other side of the 6V6 resistor (6V6 bias amp). Note the reading displayed on the voltmeter.
Disconnect the DC voltage regulator. Attach the 1 mega-ohm resistors to the two "Input" terminals and reconnect the DC voltage regulator. Note the voltage output reading using the resistors with the voltmeter.
Subtract the voltage reading in Step 2 from the voltage reading in Step 3. Divide this result by 1 mega-ohm. For example, 0.6 v - 0.3 v equals 0.3 v. Divide 0.3 v by 1 mega-ohm and the result is 0.3 amps for a 6V6 bias current.