538

• alternative name: Hickock

Hickok 538 Tube Tester. 

Similar to 536 except that 538 includes a VOM. The 6H6 tubes are only for AC rectification; this is not a VTVM. 

It is different from the later 538A as it has separate controls for the Micromho scale and signal volts. The later 538A built this into one control, like the 539. A roll chart indicates when the low-signal switch should be selected. 

A few notes I have found on this tester suggest that the "Good/Bad" scale can be used to do a simple emission test on most tubes, but the roll chart that was installed in this particular tester did not have the "English" setting required to set up the tester to perform this. Practically speaking, the "English" setting and knob are only used on diodes and rectifier tests, as in other later Hickok models. 

Not very well documented in modern times, I haven't been able to find much else save some other pictures of others' examples of this tester. The 538 schematic that is found online is actually for the 538A, not the 538. 

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Tous les appareils de Hickok Electrical Instrument Co.; Cleveland, OH