?

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, René