On Sunday, November 18, 2018 at 5:14:51 AM UTC-5, Phil Allison wrote:
wrote:


I'm restoring a couple of 1970's wooden case acoustic coupler, both made in
the UK.
I haven't find the slightest bit of information about both of them, just
some pictures on the net.
One of them is the DCD model AC.350.OM (where probably OM stands for
Originate, as it doesn't have any Orig/Answ switch).
Now, I'm checking most parts (it's made on 6 PCBs, plus some chassis-mounted
components) for obvious problem, like diode/BJT junctions, carbon composition
resistors values, electrolytic ESR/shorts etc.
All transistor have MAxxxx or MExxxx codes, they really look like BCxxx
transistors from the early 1970's, one of the most common ones is ME4101.
By the way, the ICs have 1972-1974 date codes, so this unit was probably
manufactured in 1974.
My first question is: does anyone have a cross reference for these MA/ME
transistors? Are those a kind of military markings?
Second question: almost all ME4101 have a junction voltage drop around 0.8V
but one of them shows a bit more than 1V drop on both BE and BC junctions
(it's NPN). Can I assume this one must be bad?
Any other hint and information is welcome.


** ME4101 etc devices were made by " Micro Electronics" of the USA - Silicon Valley address.

http://www.microelect.com/

Made a lot of types in TO106 package - shiny, glob tops and gold plated leads.

Very neat looking.


.... Phil



You got me curious. Here's a link to a picture. I remember seeing similar transistors years ago in Zenith TVs.

https://www.radiomuseum.org/images/t...n/me4101_1.jpg