[time-nuts] Tektronix TM500 Series Help

[Don @ True-Cal]

Happy New Year to all!

In working on my TM501 which serves as the power supply for my AM503B current probe, I had to dismount the 2 series pass transistors from the TM case (heat sink). After repair (filter caps) and during remounting the circuit board, Q12 transistor TO-127 case fractured while bending the leads. This transistor is one of the two series pass transistors that some TM-Series modules use as external mounted power devices. These two transistors are used mostly with PSxxx power supply modules. They are not actually used as active components of the TM501 and fortunately for me, not used with the AM503B module so I am up and running again. I would like to fix this situation so I could use this TM501 with any/all modules.

The manual (and device) says Q12 is an NPN, SI, Selected, TO-127 SJE924. For completeness, the complementary Q10 is a PNP, SI, TO-127 SJE925. These transistors types are the same across any TM-Series mainframe.

I can't find any SJE or MJE 9xx reference. Does anyone have a cross reference or know of a substitute device for these transistors? I tried a MJE3055 which is very general purpose and it does not work with a PS503A power supply module. This, plus the word "Selected" in the manual, says to me that something (Hfe?) must be fairly critical. Another alternative is someone with a junker TM mainframe that would be willing to pull one or both of these transistors.

Regards...
Don