[time-nuts] Tektronix TM500 Series Help

[Charles P. Steinmetz]

Don wrote:

>1) The devices in any of my TM mainframes are NOT Darlingtons.
>2) The actual Q12 device in my TM501 is stamped SJE924 (Tek PN 151-0349-00)
>
>These two facts seem contradictory with copied Motorola Data Sheet 
>info but I going with what I see in front of me.

If you have a device marked SJE924 and/or 925 and it is not broken 
and not a darlington, then it is almost certain that either the old 
Motorola databook or my copying was in error.  It is probably moot, 
as the chance of finding more transistors so marked today appears about nil.

In any case, rest assured that the TM5xx mainframes do NOT use 
darlingtons.  So, your alternatives appear to be:

a.  Buy an old stock Tek 151-0349-00 from someone like Sphere
b.  Buy an NTE182 (NPN) [NTE183 is the PNP complement] from wherever 
you can find one
c.  Adapt a transistor in a different package, either by mounting it 
upside-down or by using crossed wire leads (personally, I would opt 
for the latter to keep the heatsinking integrity)

>I still don't know why the MJE3055 didn't work as it is not that 
>different from the MJE2801 in this application.

If it was a functional MJE3055 in a TO-127 package, I don't see why, 
either.  Did you check the pinout before you installed it, and was it 
really ECB?  As you have seen, these days the MJE3055 is available 
much more commonly in the "-T" version (TO-220 package, BCE).  Could 
it be that the manufacturer built "non-T" MJE3055s in the TO-127 
physical package, but with the TO-220 pinout?

Best regards,

Charles