Weston 981 Type 3 Tube Tester


This is a Weston 981 Mutual Conductance tube tester that was not functional when I received it for calibration.  One of the electrolytic capacitors was shorted and blew a fuse when the line adjust was turned up.  This tube tester uses selenium rectifiers instead of vacuum tube rectifiers.  The selenium rectifiers should not be replaced with solid state diodes because this affects the calibration of the tube tester.  The tester was designed for the voltage drop across the selenium rectifier and is difficult to replicate with solid state diodes.  Luckily the selenium rectifier was not affected by the shorted capacitor.  The line adjust was pot was also bad and had to be replaced.  The line adjust pots in the old tube testers are wire wound pots with around 25 watt handling capability.  They are still available in NOS or as new units.

This tube tester is a mutual conductance tube tester and provides good quality testing of vacuum tubes.

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