I think you are right Dave about the 2SA1145, I just bought a bunch from a guy in Poland on eBay. I only have to fiddle with the connections because the base is not in the centre but this is not a big problem.
The BC556b?s functioning good but in the beginning of the trace you see that especially the start of the trace is a bit vague. Maybe it has to do that the Cc is 8pF. So way more then the 2pF from the 2N2207.
So thanx for the advice!
toggle quoted message
Show quoted text
--- In TekScopes@..., David Wise <david_wise@...> wrote:
In my opinion, the 2SA1145 is your best bet from Mouser. It specifically lists low Cob as a feature, and it's 2.5pF typical at 10V, and fT=200MHz. KSA992 is runner-up with 2pF typical at 30V and fT=100MHz. Both are cheap and plentiful. Get them while they still are.
Dave Wise
________________________________
From: TekScopes@... [mailto:TekScopes@...] On Behalf Of G. K.
Sent: Tuesday, October 09, 2012 8:10 PM
To: TekScopes@...
Subject: Re: [TekScopes] Re: Bright dots at start of the trace on a 547
Here is another choice, Vcbo =-120V, Ccbo ~ 2-3 pF, Ft ~ 100MHz. (Mouser 7 cents each!) - George
From: David <davidwhess@...>
To: TekScopes@...
Sent: Tuesday, October 9, 2012 7:23 PM
Subject: Re: [TekScopes] Re: Bright dots at start of the trace on a 547
Both of the ones I listed are available from Mouser. The 2N5401 and
2N6520 both have a Cob of 6.0pF maximum at 10 and 20 volts
respectively but Cobo falls with Vcb so at 60 volts it will be
significantly lower. From the graph of Cob versus voltage, it looks
like they both could easily be 2.5pF at 60 volts.
On Tue, 9 Oct 2012 17:17:25 -0700, David Wise <mailto:david_wise%40phoenix.com>
wrote:
MPSA92 is the only through-hole hit at Mouser, but I think Cob is too high.
A couple of SMT parts are 4pF vs 6. FJX99T, 2SA1312, and 2SA1136.
Dave Wise
-----Original Message-----
From: mailto:TekScopes%40yahoogroups.com
[mailto:mailto:TekScopes%40yahoogroups.com] On Behalf Of mailto:larrys%40teamlarry.com
Sent: Tuesday, October 09, 2012 4:57 PM
To: mailto:TekScopes%40yahoogroups.com
Subject: Re: [TekScopes] Re: Bright dots at start of the trace on a 547
Comp PNP should be MPSA92 / 93
-ls-
"Tom Jobe" <mailto:tomjobe%40gmail.com> wrote:
Hi George,
Those NPN transistors are a nice find!
Thank you for the link to the datasheet.
Is there a PNP version?
I think that is what they are looking for.
tom jobe...
----- Original Message -----
From: G. K.
To: mailto:TekScopes%40yahoogroups.com
Sent: Tuesday, October 09, 2012 4:31 PM
Subject: Re: [TekScopes] Re: Bright dots at start of the trace on a
547
How about the MPSA42 and 43?
( ). Both
are high voltage and reasonable fast. Mouser has stock, and they are
cheap. - George
From: David <mailto:davidwhess%40gmail.com>
To: mailto:TekScopes%40yahoogroups.com
Sent: Tuesday, October 9, 2012 3:27 PM
Subject: Re: [TekScopes] Re: Bright dots at start of the trace on a
547
The specifications I found for the 2N2207 were Vceo = 50 volts and
Vcbo = 70 volts. When the blanking signal is applied to the emitter
and the base driven by a relatively low impedance -0.6 volts, the
Vcbo
is a better match.
But even a Vcbo of 70 volts is not much greater than the -68 volts
marked on the schematic. Maybe Tektronix graded them for a higher
minimum breakdown voltage.
On Tue, 09 Oct 2012 21:31:25 -0000, "Albert"
<mailto:aodiversen%40online.nl>
wrote:
No, for 151-063 (= 2N2207) Vceo = 70 V, but even then ...
Albert
Hi David,
you say "operating close to its breakdown voltage", then you are
joking.
V_ceo is 50 volts and in the schematics, the difference
between E
and C
is over 67 volts !!
They are working "beyond the cliff" !
Herbert
------------------------------------
Yahoo! Groups Links
