You must measure mV on the mentioned resistor. Set up your DMM to 2VDC and measure the changing voltage on the mentioned (emitter) resistor. Other option measure mA between the power transformer and the PCB plus connector. Of course you must disconnect the wire and use your DMM measuring mA. It is easy to set it up. Be careful with that trimmer because you can blew up your amp (do not just adjust without measurements). Also use a dim light bulb on the AC input to protect your amplifier while you set it up. See the att. picture. I hope this helps.
