Comes with a pair of octal testers.

The Bias Rite Cathode Current Monitor is a self contained unit designed to allow the user to set the desired idle cathode current value with the G1 bias control. Two adapter sockets are provided so the power supply may be loaded as it would be in normal operation, an important feature since most amplifier power supplies are unregulated. The Bias Rite is supplied with an integral digital readout which measures the cathode current to the tenth of a milliamp over a range of 1 to 199 milliamps. Power is supplied by an internal 9 volt battery.

The VI switch allows one to switch the digital meter between reading plate voltage and cathode current. This allows one to quickly calculate plate dissipation to ensure that the operating parameters of the output tubes are within a safe range. The VI switch is standard on all complete models.

Please Note: The locator pin in the center of the male octal plug is sensitive to breakage from twisting or lateral (sideways) force. It will break or crack and then it will be difficult to locate the proper pin orientation for re-insertion of the adapter head into the socket. An incorrect installation may damage your amp, the Bias Rite, or both. You must take great care in inserting the bias rite head in the socket. The best method is to set the head adapter on the socket and lightly turn the head until you feel it drop into the socket holes. Also keep the head straight up (perpindicular, vertical right angle) from the tube socket, and push straight down. Do not wiggle, twist, or allow it to be insterted at an angle. If you do break a locator pin, it can be repaired using thick gel super glue.