[time-nuts] Tektronix TM500 Series Help

[Don @ True-Cal]

Thanks everyone for some good information. Here is what I know for sure from testing, observation and more searching.

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.

3) Another source also cross referenced the MJE2801 as a substitute for the SJE924 (NPN) and a MJE2901 for the SJE925 (PNP).

These substitutes will be my next try but I don't have either one so will have to order them. I still don't know why the MJE3055 didn't work as it is not that different from the MJE2801 in this application.

The substitute MJE... devices come as TO-220 (BCE) with "T" suffix as in MJE2x01T. This is the more common and readily available version. If I can't find a good source for the TO-127 MJE2801 (ECB) version, I will have to mount it upside down.

Regards...
Don


  ----- Original Message ----- 
  From: Don Latham 
  To: Discussion of precise time and frequency measurement 
  Sent: Sunday, January 03, 2010 3:28 PM
  Subject: Re: [time-nuts] Tektronix TM500 Series Help


  These external transistors are shown on the PS503 as single transistors,
  and they are driven by a single stage transistor from an op amp.The
  external pass transistors for each plug-in could use NTE182 (NPN) and
  NTE183(PNP). IMHO, the hfe of the NTE devices will be entirely adequate,
  and they're cheap as well. I think I used one of these to repair a 500
  series p/s in the past. It's worth a try.
  Don


  Charles P. Steinmetz
  > Mark wrote:
  >
  >>The mainframe power transistors are NOT darlingtons.  They are plain
  >>NPN/PNP power transistors with non-standard pinouts.
  >
  > The TO-127 pinout is ECB -- most other plastic power transistor
  > packages are BCE.
  >
  > I just pulled the cover off a TM503, and the 151-0349-00 (and
  > 151-0373-00) devices in it are NOT darlingtons.
  >
  > At least some Tek manuals say the 151-0349-00 devices are SJE924s,
  > and the information I have on those (which I copied from a now long
  > lost Motorola databook of the era) indicates that they are
  > darlingtons (there is some corroboration for this on the web, but I
  > have not found a web datasheet).  However, a current source of Tek
  > parts (see below) says that its 151-0349-00 devices are MJE2801s,
  > which I believe are not darlingtons.  So, either Tek was incorrect in
  > stating that P/N 151-0349-00 = SJE924, or the Motorola datasheet I
  > copied from was wrong that SJE924s are darlingtons, or I copied
  > wrong.  (Surely it couldn't be the third?   ;-)   In any case, it
  > does not appear that the transistors in TM5xx frames are darlingtons.
  >
  > If anyone wants original form factor TO-127 transistors (presumably
  > Tek old stock, marked "034900"), they are available from:
  >
  > http://www.sphere.bc.ca/test/tek-parts/tekparts2.html
  >
  > Best regards,
  >
  > Charles
  >
  >
  >
  >
  >
  >
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  -- 
  Dr. Don Latham AJ7LL
  Six Mile Systems LLP
  17850 Six Mile Road
  POB 134
  Huson, MT, 59846
  VOX 406-626-4304
  www.lightningforensics.com
  www.sixmilesystems.com


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