Bias Probe (Current Measuring)


Our bias probe measures true bias current. For use with octal tubes EL34, E34L, 6CA7, KT66, KT77, 6L6, 6V6, 5881, 6550, KT88, KT90. The Granger Amp bias probe measures in milliamps by insertion into the cathode connection that conducts the current to the plate (anode) of the tube.

When using our probe the user sets their multimeter to the DC mA setting (not DC Volts!),  and selects a range of 200 milliamps if the meter is not auto sensing. Then insert the red plug into the jack labeled mA and the black plug into the common ( – or NEG) jack. The bias probe is placed into one of the amp’s power tube sockets and the tube into the bias probe. This is the most accurate way of measuring bias current, and only takes a few minutes to properly bias an amp that has a fixed, adjustable bias supply. Octal socket pins 1,2,3,4,5,6, and 7 are wired pass-through.

Please note – if your meter will not read above 0mA, disconnect the probe from meter, open the meter (usually screws on the meter’s back panel), and verify the internal fuse is good and has continuity. Product color and wire color may vary from product photo.

Pricing and Options


6 in stock (can be backordered)


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