[time-nuts] HP 106B quartz frequency standard...the story so far

[Mark Sims]

The 2N1701 is a general purpose transistor rated at 60V,  2.5A.   Problem is it is in a TO-8 package.  You probably won't find an exact replacement as this package is rather rare.  You should be able work in a TO-220 or smaller packaged device.  NTE lists a cross reference for the device.  Watch the pinouts.  Canned devices usually go E-B-C.  TO220's usually go E-C-B.

A 1V drop across the regulator pass transistor could be due to a shorted pass transistor,  but is on the high end of what you would expect to see with this kind of fault.  My bet is something else in the regulator.  If there is an op amp (usually a 741) acting as the error amp,  I would start looking there.  This is a very common part to see fail in this application in equipment of this vintage.  

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