Good catch there Dave. I have noticed when testing my curve tracer on
2N3906 and 2N3904 transistors that they often operate significantly
higher than their rated breakdown voltage but it sure is not something
I would want to rely on without grading them. The specifications I
see for the 2N2207 show it to be operating close to its breakdown
voltage.
Offhand I would try a 2N5401 or 2N6520 as a replacement and check all
of the 2N2207 transistors.
On Tue, 9 Oct 2012 10:47:35 -0700, David Wise <david_wise@...>
wrote:
Q184 sees up to about 75V from collector to emitter. The 2N3906 is
only rated 40V. Even if it doesn't break down, you may find that the trace
unblank is a little bit slow, because the original transistor had quite a low Cob.
I can't suggest a better one, though. Maybe something for video amp service?
Dave Wise
-----Original Message-----
From: TekScopes@...
[mailto:TekScopes@...] On Behalf Of tek_547
Sent: Tuesday, October 09, 2012 10:17 AM
To: TekScopes@...
Subject: [TekScopes] Re: Bright dots at start of the trace on a 547
Thanx for all the reactions guys, it was an old germanium
transistor Q184 in the unblanking circuit. Chuck did me the
suggestion to look specific at that transistor and he was damn right.
I replaced it for a 2N3906 and also his brother on the A
timebase Q373. They are silicium transistors but functions perfectly.
So in a few days, problem solved :-)
The only thing what?s left is the timing from the sweep rates,
they are about 20% to long. All of them on both timebases, so
if somebody knows...
grtz and thanx so far for all the help, Ren¨¦
David Hess