[GreenKeys] Model 33 Q1 transistor replacement

[Paul Newland, ad7i]

It's probably not all that difficult to find a working replacement, but in
a different form factor.   Can you show a larger portion of the schematic?
I'd like to see if this transistor is operating as an on/off switch, or if
it's trying to work some magic to regulate the voltage on the magnet for
fast pull in and then low current idle.

Some basic DC measurements might give you some insight into the health of
the transistor without removing it from the circuit board.
I'd be curious to know the voltage from base to emitter when the transistor
is "ON" (or supposed to be on).   Also (can't see that part of the
schematic) but if there's a resistor in series with the base I'd be curious
to know the voltage across the resistor (and the resistance of the
resistor), and then use ohms law to determine the base current.  Same thing
for the selector magnet current, if that's possible.

Paul, ad7i


On Mon, Jul 21, 2025 at 10:22 AM Erik Bruchez <erik at bruchez.org> wrote:

> Hi all,
>
> I am trying to troubleshoot a Model 33 selector magnet circuit. I don't
> know for sure yet but there is a chance that it's the Q1 transistor on the
> board. I am wondering if anybody here has ever replaced this transistor,
> and if so with what (possibly more modern) part. The original is
> Motorola-branded and labeled 181671. The schematics call it a "high gain"
> transistor.
>
> -Erik
>
> [image: C6BC2216-1423-4DCB-A6BF-7869D424140C.JPG]
>
> ______________________________________________________________
> GreenKeys mailing list
> Home: http://mailman.qth.net/mailman/listinfo/greenkeys
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:GreenKeys at mailman.qth.net
>
> >>> Jordan Spencer Cunningham's GreenKeys Search Tool:
> https://teletype.net/gksearch
> >>> 2002-to-present greenkeys archive:
> http://mailman.qth.net/pipermail/greenkeys/
> >>> 1998-to-2001 greenkeys archive:
> http://mailman.qth.net/archive/greenkeys/greenkeys.html
> >>> Randy Guttery's 2001-to-2009 GreenKeys Search Tool:
> http://comcents.com/tty/greenkeyssearch.html
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to ad7i at ad7i.net
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.qth.net/pipermail/greenkeys/attachments/20250721/8c38b854/attachment-0001.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: C6BC2216-1423-4DCB-A6BF-7869D424140C.JPG
Type: image/jpeg
Size: 5479429 bytes
Desc: not available
URL: <http://mailman.qth.net/pipermail/greenkeys/attachments/20250721/8c38b854/attachment-0001.jpe>