Re: Bright dots at start of the trace on a 547
You have more data than I. But consider the application. It has to
generate a 70V step, as fast as possible, but the most important part
is the last little bit, otherwise the trace will be dim at the start of
the fastest sweeps. Note that they put in a resistor that isolates the
anti-saturation clamp diode from the base - that could only be to
minimize C-B capacitance outside the transistor. The transistor is
driving a high-impedance load; I don't see current-handling ability
figuring very large. But the ultimate test is to pop in a candidate
and give it a spin. Yay sockets!
Dave Wise
toggle quoted message
Show quoted text
-----Original Message-----
From: TekScopes@...
[mailto:TekScopes@...] On Behalf Of David
Sent: Wednesday, October 10, 2012 1:13 PM
To: TekScopes@...
Subject: Re: [TekScopes] Re: Bright dots at start of the trace on a 547
I found a bunch of different Cob values (up to 12pF!?) for the 2N2207
with unclear test conditions so I am not convinced 2.5pF Cob is a
magic value. Low Ic small junction transistors are not as common as
they used to be and I suspect the better gain characteristics of an Ic
200mA transistor might make up for the higher output capacitance of
the larger junction in this case.
The 547 I recently acquired works fine as far as I can tell except for
dirty switches and potentiometers but I have started taking notes on
it.
On Wed, 10 Oct 2012 09:39:47 -0700, David Wise
<david_wise@...> wrote:
Good catch, George. I only searched for "-300V" to "-70V", forgetting that the staff is sloppy about voltage polarities.
Searching for positive breakdown voltages yields many many hits.
And good point, David Hess, but the 2N2207's 2.5pF Cob is specified at 6V.
Dave Wise
|
Re: Tantalums cant take surges. (Subject was Aluminiumversus Tantalum Electrolytics)
That explains that then, they measure a few percent lower at 1kHz.
It's unfair to accuse a manufacturer of penny pinching if you don't
meet their specified testing conditions (usually 120Hz).
Saving a few percent of foil is probably not worth the hassle of
having to meet tighter tolerances caused by leaning towards the lower
end. More likely they used to go above nominal with the old caps
because tolerances were asymmetrical back then.
I'll check out the test data to see if the distribution is offset when
I get the chance.
ST
toggle quoted message
Show quoted text
On Wed, Oct 10, 2012 at 10:23 PM, Sergey Kubushyn <ksi@...> wrote: On Wed, 10 Oct 2012, Stefan Trethan wrote:
At 1kHz that's just about spot on specification for the taiyo yuden part.
The impedance at this frequency will be what, 15, 16 Ohms? Not sure
why you'd worry.... I do not worry. It is not about using it at a particular frequency.
At what frequency did you measure capacitance? Just so that we don't
waste both our time again. 1KHz. And I don't have time to waste too.
ST
On Wed, Oct 10, 2012 at 9:22 PM, Sergey Kubushyn <ksi@...> wrote:
On Wed, 10 Oct 2012, Stefan Trethan wrote:
On Wed, Oct 10, 2012 at 6:59 PM, Sergey Kubushyn <ksi@...> wrote:
There were bunch of 10uF 25V ones
that I was going to replace with 1206 SMD X5R ceramics but to my surprise
those dipped tantalums had something like 300mOhm ESR that is actually
BETTER than ceramics (Taiyo Yuden 10uF 25V 1206 X5R ceramics of recent
manufacturing that I had several reels in my parts bins have something like
350mOhms ESR.) At what frequency? The ceramic should have well below 10mR at 100kHz
according to specification, and I just don't see how it could be
otherwise considering the construction. 1KHz. This is actual measured values. As for the specifications majority of
manufacturers don't give any values on ESR in their datasheets. It is
"common knowledge" they are "very low ESR" but reality check shows totally
different picture. If you look at e.g. NIC NMC High CV Series datasheet (one
of the few who give data on ESR) you'll see a ESR vs Frequency chart. It
clearly shows that MLCCs are better when going into MHz range but they are
nothing to write home about at lower frequencies.
Regarding the generally low capacitance value on electrolytics, I have
extensive test data for Rubycon and Nippon Chemicon at work and will
check if they are consistently at the lower capacitance tolerance. Once again, I do NOT have very extensive data, just several hundred
capacitors. It might be not a representative sample but I could not find a
SINGLE one of recent manufacturing that was 100% of stated capacity or
higher. On the old ones I could not find more than couple of pieces that
were under 100%.
ST
------------------------------------
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---
*
* KSI@home KOI8 Net < > The impossible we do immediately. *
* Las Vegas NV, USA < > Miracles require 24-hour notice. *
*
------------------------------------
Yahoo! Groups Links
------------------------------------
Yahoo! Groups Links
---
*
* KSI@home KOI8 Net < > The impossible we do immediately. *
* Las Vegas NV, USA < > Miracles require 24-hour notice. *
*
------------------------------------
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|
Re: Tantalums cant take surges. (Subject was Aluminiumversus Tantalum Electrolytics)
On Wed, 10 Oct 2012, Stefan Trethan wrote: At 1kHz that's just about spot on specification for the taiyo yuden part.
The impedance at this frequency will be what, 15, 16 Ohms? Not sure
why you'd worry.... I do not worry. It is not about using it at a particular frequency. At what frequency did you measure capacitance? Just so that we don't
waste both our time again. 1KHz. And I don't have time to waste too.
ST
On Wed, Oct 10, 2012 at 9:22 PM, Sergey Kubushyn <ksi@...> wrote:
On Wed, 10 Oct 2012, Stefan Trethan wrote:
On Wed, Oct 10, 2012 at 6:59 PM, Sergey Kubushyn <ksi@...> wrote:
There were bunch of 10uF 25V ones
that I was going to replace with 1206 SMD X5R ceramics but to my surprise
those dipped tantalums had something like 300mOhm ESR that is actually
BETTER than ceramics (Taiyo Yuden 10uF 25V 1206 X5R ceramics of recent
manufacturing that I had several reels in my parts bins have something like
350mOhms ESR.) At what frequency? The ceramic should have well below 10mR at 100kHz
according to specification, and I just don't see how it could be
otherwise considering the construction. 1KHz. This is actual measured values. As for the specifications majority of
manufacturers don't give any values on ESR in their datasheets. It is
"common knowledge" they are "very low ESR" but reality check shows totally
different picture. If you look at e.g. NIC NMC High CV Series datasheet (one
of the few who give data on ESR) you'll see a ESR vs Frequency chart. It
clearly shows that MLCCs are better when going into MHz range but they are
nothing to write home about at lower frequencies.
Regarding the generally low capacitance value on electrolytics, I have
extensive test data for Rubycon and Nippon Chemicon at work and will
check if they are consistently at the lower capacitance tolerance. Once again, I do NOT have very extensive data, just several hundred
capacitors. It might be not a representative sample but I could not find a
SINGLE one of recent manufacturing that was 100% of stated capacity or
higher. On the old ones I could not find more than couple of pieces that
were under 100%.
ST
------------------------------------
Yahoo! Groups Links
---
*
* KSI@home KOI8 Net < > The impossible we do immediately. *
* Las Vegas NV, USA < > Miracles require 24-hour notice. *
*
------------------------------------
Yahoo! Groups Links
------------------------------------
Yahoo! Groups Links
--- * * KSI@home KOI8 Net < > The impossible we do immediately. * * Las Vegas NV, USA < > Miracles require 24-hour notice. * *
|
Re: tds 700c field adjusting software
--- In TekScopes@..., "serg34@..." <serg34@...> wrote:
This is shot in the dark, but I had to try:
I found service manual with disks for TDS 500C, 600C and 700C, but disks do not read on any of my ancient 3.5" drives. Does anyone have that software or any idea how to get it? So far I am trying to read those disks, using various contraptions. The reason I try to get this software is that I wanted to try it with tds784c manufactured in 97. Vref calibration was my #1 project. Forgive my foray into TDS world on this forum please.
Thank you.
Serg.
---------
Contact me off list for a copy. /H?kan
|
Re: Bright dots at start of the trace on a 547
I found a bunch of different Cob values (up to 12pF!?) for the 2N2207 with unclear test conditions so I am not convinced 2.5pF Cob is a magic value. Low Ic small junction transistors are not as common as they used to be and I suspect the better gain characteristics of an Ic 200mA transistor might make up for the higher output capacitance of the larger junction in this case. The 547 I recently acquired works fine as far as I can tell except for dirty switches and potentiometers but I have started taking notes on it. On Wed, 10 Oct 2012 09:39:47 -0700, David Wise <david_wise@...> wrote: Good catch, George. I only searched for "-300V" to "-70V", forgetting that the staff is sloppy about voltage polarities.
Searching for positive breakdown voltages yields many many hits.
And good point, David Hess, but the 2N2207's 2.5pF Cob is specified at 6V.
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
|
Re: Tantalums cant take surges. (Subject was Aluminiumversus Tantalum Electrolytics)
At 1kHz that's just about spot on specification for the taiyo yuden part.
The impedance at this frequency will be what, 15, 16 Ohms? Not sure
why you'd worry....
At what frequency did you measure capacitance? Just so that we don't
waste both our time again.
ST
toggle quoted message
Show quoted text
On Wed, Oct 10, 2012 at 9:22 PM, Sergey Kubushyn <ksi@...> wrote: On Wed, 10 Oct 2012, Stefan Trethan wrote:
On Wed, Oct 10, 2012 at 6:59 PM, Sergey Kubushyn <ksi@...> wrote:
There were bunch of 10uF 25V ones
that I was going to replace with 1206 SMD X5R ceramics but to my surprise
those dipped tantalums had something like 300mOhm ESR that is actually
BETTER than ceramics (Taiyo Yuden 10uF 25V 1206 X5R ceramics of recent
manufacturing that I had several reels in my parts bins have something like
350mOhms ESR.) At what frequency? The ceramic should have well below 10mR at 100kHz
according to specification, and I just don't see how it could be
otherwise considering the construction. 1KHz. This is actual measured values. As for the specifications majority of
manufacturers don't give any values on ESR in their datasheets. It is
"common knowledge" they are "very low ESR" but reality check shows totally
different picture. If you look at e.g. NIC NMC High CV Series datasheet (one
of the few who give data on ESR) you'll see a ESR vs Frequency chart. It
clearly shows that MLCCs are better when going into MHz range but they are
nothing to write home about at lower frequencies.
Regarding the generally low capacitance value on electrolytics, I have
extensive test data for Rubycon and Nippon Chemicon at work and will
check if they are consistently at the lower capacitance tolerance. Once again, I do NOT have very extensive data, just several hundred
capacitors. It might be not a representative sample but I could not find a
SINGLE one of recent manufacturing that was 100% of stated capacity or
higher. On the old ones I could not find more than couple of pieces that
were under 100%.
ST
------------------------------------
Yahoo! Groups Links
---
*
* KSI@home KOI8 Net < > The impossible we do immediately. *
* Las Vegas NV, USA < > Miracles require 24-hour notice. *
*
------------------------------------
Yahoo! Groups Links
|
Re: Tantalums cant take surges. (Subject was Aluminiumversus Tantalum Electrolytics)
On Wed, 10 Oct 2012, Stefan Trethan wrote: On Wed, Oct 10, 2012 at 6:59 PM, Sergey Kubushyn <ksi@...> wrote:
There were bunch of 10uF 25V ones
that I was going to replace with 1206 SMD X5R ceramics but to my surprise
those dipped tantalums had something like 300mOhm ESR that is actually
BETTER than ceramics (Taiyo Yuden 10uF 25V 1206 X5R ceramics of recent
manufacturing that I had several reels in my parts bins have something like
350mOhms ESR.) At what frequency? The ceramic should have well below 10mR at 100kHz
according to specification, and I just don't see how it could be
otherwise considering the construction. 1KHz. This is actual measured values. As for the specifications majority of manufacturers don't give any values on ESR in their datasheets. It is "common knowledge" they are "very low ESR" but reality check shows totally different picture. If you look at e.g. NIC NMC High CV Series datasheet (one of the few who give data on ESR) you'll see a ESR vs Frequency chart. It clearly shows that MLCCs are better when going into MHz range but they are nothing to write home about at lower frequencies. Regarding the generally low capacitance value on electrolytics, I have
extensive test data for Rubycon and Nippon Chemicon at work and will
check if they are consistently at the lower capacitance tolerance. Once again, I do NOT have very extensive data, just several hundred capacitors. It might be not a representative sample but I could not find a SINGLE one of recent manufacturing that was 100% of stated capacity or higher. On the old ones I could not find more than couple of pieces that were under 100%.
ST
------------------------------------
Yahoo! Groups Links
--- * * KSI@home KOI8 Net < > The impossible we do immediately. * * Las Vegas NV, USA < > Miracles require 24-hour notice. * *
|
Re: Bright dots at start of the trace on a 547
I see a lot of replacement possibilities, but over a week or so I place an order at Conrad here in Holland, so I get to figure out what substitues I can take there.
From the afternoon till now (4 hours) the 547 is running fine and I also changed the 2N3906 for two BC556b, so a big smile :-)
Thanx everybody so far for the constructive thinking about the problem, Ren¨¦
toggle quoted message
Show quoted text
--- In TekScopes@..., David Wise <david_wise@...> wrote:
Looking on eBay now. 2N5401 is 6pF max instead of typical.
NTE2634 looks good although it's a TO-126 package. Only 2pF! $1.38 free shipping.
NTE2502 maybe too.
Dave Wise
-----Original Message-----
From: David Wise
Sent: Tuesday, October 09, 2012 5:17 PM
To: 'TekScopes@...'
Subject: RE: [TekScopes] Re: Bright dots at start of the trace on a 547
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: TekScopes@...
[mailto:TekScopes@...] On Behalf Of larrys@...
Sent: Tuesday, October 09, 2012 4:57 PM
To: TekScopes@...
Subject: Re: [TekScopes] Re: Bright dots at start of the trace on a 547
Comp PNP should be MPSA92 / 93
-ls-
"Tom Jobe" <tomjobe@...> 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: TekScopes@...
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 <davidwhess@...>
To: TekScopes@...
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
|
tds 700c field adjusting software
This is shot in the dark, but I had to try:
I found service manual with disks for TDS 500C, 600C and 700C, but disks do not read on any of my ancient 3.5" drives. Does anyone have that software or any idea how to get it? So far I am trying to read those disks, using various contraptions. The reason I try to get this software is that I wanted to try it with tds784c manufactured in 97. Vref calibration was my #1 project. Forgive my foray into TDS world on this forum please.
Thank you.
Serg.
|
Re: Jumpy trigger control on Tektronics 475
Thanks for the reply. I'm checking the power supply. I'm pretty sure that's were the problem lies. I hoping to replace the caps. and rectifier if I have to. I'm hoping I can use slightly over rated Caps.Your input on that would be great.
Thanks, Derek
toggle quoted message
Show quoted text
--- In TekScopes@..., David <davidwhess@...> wrote:
I noticed that and wonder if the relatively low video camera frame
rate is disguising what is really going on.
On Mon, 08 Oct 2012 22:08:41 -0400, "Tom Miller"
<tmiller11147@...> wrote:
I would open it up and check the power supplies for voltage and ripple per the manual. It seems to be jumping sync at a periodic rate.
|
Re: Tantalums cant take surges. (Subject was Aluminiumversus Tantalum Electrolytics)
On Wed, Oct 10, 2012 at 6:59 PM, Sergey Kubushyn <ksi@...> wrote: There were bunch of 10uF 25V ones
that I was going to replace with 1206 SMD X5R ceramics but to my surprise
those dipped tantalums had something like 300mOhm ESR that is actually
BETTER than ceramics (Taiyo Yuden 10uF 25V 1206 X5R ceramics of recent
manufacturing that I had several reels in my parts bins have something like
350mOhms ESR.) At what frequency? The ceramic should have well below 10mR at 100kHz according to specification, and I just don't see how it could be otherwise considering the construction. Regarding the generally low capacitance value on electrolytics, I have extensive test data for Rubycon and Nippon Chemicon at work and will check if they are consistently at the lower capacitance tolerance. ST
|
Re: Bright dots at start of the trace on a 547
Good point Albert, I see what you mean and I just checked it. With a 1KHz signal (1mS) there are about 11.5 cycles when I turn the horizontal position from left to right. So when I "compress" the picture, in simple words, there are two possibilities;
- the length of the visible trace becomes shorter till we have 10 divisions but without changing the individual time length of one cycle. Thus still having the problem. or;
- the total length of the trace is more compressed (it is now about 12.5 div in display length) till there are exact 10 divisions. And also "compressing" the individual cycle time wich is now 20% to much.
I think indeed that the second option is the way to the solution.
Good point from you!
I have just changed the two 2N3906 with two BC556b (Vceo 65V) because they are not adekwate for this voltage, as some of you said.
In the future I search for a permanent replacement that can withstand a higher voltage but until now the BC556b?s doing their work perfect.
Now I have to dig in the schematics and try to understand what the possible cause can be why the sweeplength is so long.
grtz and thanx for all the help, Ren¨¦
toggle quoted message
Show quoted text
--- In TekScopes@..., "Albert" <aodiversen@...> wrote:
Hi Ren¨¦,
Not sure what you mean with "too long".
If you display 1 kHz signal at 1 ms/div, then
- each period is 1.2 div and there are about 10 periods visible if you rotate Hor Pos to see start and end.
In this case the gain of the Hor Output Amplifier seems too high for some reason.
-- or --
- each period is 1.2 div and there are only about 8-8.5 periods visible, even if you rotate Hor Pos.
This would indicate too fast timing of the sweep generators. This seems not realistic when both A and B suffer from this by such a big percentage.
Albert
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¨¦
|
Re: Bright dots at start of the trace on a 547
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
toggle quoted message
Show quoted text
Here is another choice, ?
Vcbo =-120V, Ccbo ~ 2-3 pF, Ft ~ 100MHz. (Mouser 7 cents each!)
-?George
From: David
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" >>>
>>> 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 >> >> >> >>
|
Re: Jumpy trigger control on Tektronics 475
Thanks for the reply. I do have a service manual I downloaded. So I,m seeing about replacing the caps. on the power supply end and checking the rectifier. I'm try to see if I can over rate the new caps. a little bit because I can't find the exact values.
Thanks, Derek
toggle quoted message
Show quoted text
--- In TekScopes@..., "Tom Miller" <tmiller11147@...> wrote:
Do you have a service manual?
What does the calibration waveform look like?
How about using the HF rejection for the sync? How about the BW limit, what effect doe it have? Maybe there is some HF noise on the test signal that we can't see in the video.
Use the Norm sync mode and adjust the trigger level and show us what happens.
I would open it up and check the power supplies for voltage and ripple per the manual. It seems to be jumping sync at a periodic rate.
----- Original Message -----
From: dawtesla2
To: TekScopes@...
Sent: Monday, October 08, 2012 9:43 PM
Subject: [TekScopes] Jumpy trigger control on Tektronics 475
I got this oscilloscope a few days ago. I put up a 1 Khz sine wave (from PC sign wave gen.) to test it. But my sine wave won't stabilize. When stopped, it dances around a bit with a slight pulse. All this makes it difficult to make a proper frequency reading. It's a great scope except for that. Does anyone have any idea what the problem is?
Here's a video link
Thanks, Derek
dawtesla2@...
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Re: Tantalums cant take surges. (Subject was Aluminiumversus Tantalum Electrolytics)
On Wed, 10 Oct 2012, Dennis Tillman wrote: I've just finished "shotgun approach" rebuild of older TG501 -- almost all 74xx replaced with 74HCT/74LS, lots of resistors removed, some added (it's been done in old days when it was considered OK to leave TTL inputs floating for logical 1 so some pullups were added.) Then it came to the capacitors. The thing has a lot of dipped tantalums (no other electrolytics, everything's tantalum.) I started pulling them one by one and testing with my HP 4274A. The result was stunning -- _ALL_ of them were as good as new and even better. If you don't know almost all of modern capacitors with e.g. +/-20% tolerance come out very close to the -20% margin. Yes, they are within specs but they are ALL at the lower end. It might be there are some manufacturers that don't squeeze the last penny but everything I tested is that way. So if you have a 100uF capacitor of recent manufacturing you can be pretty sure you'll get something like 82uF. Or 88uF if you are lucky. It is NEVER 100uF not even mentioning higher than that. ALL tantalums in that TG501 (40 years old) were at least their stated capacitance and most of them were higher. There were bunch of 10uF 25V ones that I was going to replace with 1206 SMD X5R ceramics but to my surprise those dipped tantalums had something like 300mOhm ESR that is actually BETTER than ceramics (Taiyo Yuden 10uF 25V 1206 X5R ceramics of recent manufacturing that I had several reels in my parts bins have something like 350mOhms ESR.) 330uF 6V 40year old tantalum had 360uF capacitance with less than 100mOhms ESR. Only polymer aluminum types can beat that and you can be pretty sure none of 330uF ones will have 360uF capacitance. And those old tantalums never leak or dry out. If they survived that many years you can be sure they will last forever and there is absolutely no reason for replacing them. There is almost nothing better than those these days and for their longevity nothing comes even close to them. Ceramics may compete on longevity but it is not that easy to replace a 330uF capacitor with a ceramic one. And there is absolutely no advantages it would've got. Yes, tantalums do fail. But that failure rate is orders of magnitude lower than aluminum electrolytics that leak, dry out, loose their capacitance etc. Yes, aluminums fail in different way -- they just become mockups -- and tantalums fail with a short but, IMHO, it is better because you do replace them as they fail unlike aluminums that are almost dead but instrument still works somehow... The MANUFACTURER'S DATASHEETS I read specifically call out a small (10 ohm
for example) series resistor to mitigate the tantalum's known inability to
handle surges. Tek followed these guidelines.
The OTHER problems tantalums have with a short lifetime and a catastrophic
failure mechanism, that we now know so well, probably did not become fully
understood until years later after it was too late. That was not
something Tek would become aware of until it was too late.
When tantalums first became available they had some great advantages. From
an engineering perspective their size makes it possible to squeeze more
functionality into a smaller space. Their cost makes them economically
attractive and lowers instrument costs. What would you have done when
presented with this new technology?
Dennis
-----Original Message-----
From: Chuck Harris [mailto:cfharris@...]
Sent: Wednesday, October 10, 2012 5:20 AM
I suspect that tek engineers didn't put the resistors and inductors before the tantalum capacitors to protect from surges, but rather to act as an input resistor to a simple RC filter.... the network was there because they wanted to clean up the power going to subassemblies.
The fact that the small resistors and inductors acted as surge current limiters, and fuses was just a happy side benefit.
Tek engineers used the tantalums just like everyone else did during that era, as small sized large value storage capacitors that had good HF characteristics. It wasn't until much later that the capacitor manufacturers started seeing surge related failures, and began to provide warnings about limiting surge currents. They never told you to limit working voltage to 1/2 the capacitor's rated voltage... that is something that NASA learned as it tried to qualify tantalums for space use. NASA learned about the voltage issues because one of their standard ways of qualifying parts was to run them at 2x their rated voltage, which in the case of a tantalum was a disaster. Even if the part survived the testing, it was damaged and set to fail under normal operation.
-Chuck Harris
Miroslav Pokorni wrote:
Hello Dennis,
You said: "Tek engineers know this and design for it."
If that is so, how come that there are massive failures of tantalums
in 465, 7854 and other scopes.
On 10/9/2012 6:49 AM, Dennis Tillman wrote:
Tek engineers
know this and design for it.
------------------------------------
Yahoo! Groups Links
--- * * KSI@home KOI8 Net < > The impossible we do immediately. * * Las Vegas NV, USA < > Miracles require 24-hour notice. * *
|
Re: Bright dots at start of the trace on a 547
Good catch, George.? I only searched for "-300V" to
"-70V", forgetting that the staff is sloppy about voltage
polarities.
Searching for positive breakdown voltages yields many many
hits.
?
And good point, David Hess, but the 2N2207's 2.5pF Cob is
specified at 6V.
?
Dave Wise
toggle quoted message
Show quoted text
Here is another choice, ?
Vcbo =-120V, Ccbo ~ 2-3 pF, Ft ~ 100MHz. (Mouser 7 cents each!)
-?George
From: David
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" >>>
>>> 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 >> >> >> >>
|
Re: Tekronix 310 question
Those are called Black Beauty capacitors and they usually need replacement.? In fact, nearly all capacitors have limited life, with some exceptions such as ceramic.? Old gear needs the operation known colloqually as 'recapping'.? If you have the proper equipment you can test each part but lacking that, you can replace at least the larger units.
Bob
|
--- On Wed, 10/10/12, DiPaolo Richard wrote:
From: DiPaolo Richard
Subject: Re: [TekScopes] Re: Tekronix 310 question
To: "TekScopes@..."
Cc: "ditter2@..."
Date: Wednesday, October 10, 2012, 4:25 AM
?
Interesting
? ? ?? Thank you Steve. I am almost certain there are two bridge rectifier circuits I saw last night that were silicon diodes. This evening I will check into your description of the rivet interconnects. I did notice on the swing out that one of the black components with color rings on it. Old style capacitor? Was nearly split in halve. I tried reading it with a DVM. Gives me resistances in the meg ohms that keeps climbing and a small reading with the capacitance checker. Anyway, I'll look at these rivets tonight. Thank you again.?
?? All The Best, Rich D.
From: Steve
To: TekScopes@...
Sent: Wednesday, October 10, 2012 12:53 AM
Subject: [TekScopes] Re: Tekronix 310 question
?
Richard,
Following up on Bob's comments, check if the scope has been modified to silicon diodes, or does it still have the original selenium plate rectifiers? There was a mod kit to convert the scope to silicon diodes. The forward resistance of the original selenium rectifiers increases substantially as they age, so after 5 decades the forward drop will probably be lower than the regulated voltages. The resistance also increases with temperature.
Essentially, selenium rectifiers must be replaced when they are this old. But you can't just put in silicon diodes with high enough PIV ratings. Even new, the selenium rectifiers had considerable forward resistance, which was factored into the design. Silicon diodes require the addition of an additional resistor to prevent overstressing the regulator tubes. I don't know what the correct value is for the 310 scope ¨C perhaps a member who has access to the mod kit instructions will know this.
The other thing to watch out for with the original (non-`A' model) 310 is intermittent contact with the rivets which connected the two layers of the circuit boards together. Through hole plating of two sided circuit boards had not been invented when the 310 was designed. Tek used rivets pressed into holes in the board to connect the layers together. Components were soldered to the inside of the rivet, but the rivet itself relied on the tension in the flanges from when it was installed as the only contact to the circuit board traces. This proved to be extremely unreliable, forcing Tek to introduce the 310A, which was the same circuitry, but implemented on trusted ceramic strip construction.
With a lot of tenacity, it is possible to gently clean the pad area of the trace surrounding the rivet and the rivet flange itself with a small piece of steel wool. Once the oxide is removed, you can go through with a soldering iron of the proper size and tack a bit of solder to bridge the rivet flange to the trace. You only need to make the bridge in one spot, not over the entire flange area. Heat only the rivet with the soldering iron, as the foil bond to the substrate in this generation of circuit board is very intolerant of excessive heat.
- Steve
--- In TekScopes@..., Bob Albert wrote:
>
> Measure the power supply voltages.?? If they droop after a while, suspect the rectifiers.
>
> Bob
>
> --- On Tue, 10/9/12, DiPaolo Richard wrote:
>
> From: DiPaolo Richard
> Subject: [TekScopes] Tekronix 310 question
> To: " TekScopes@..." < TekScopes@...>
> Date: Tuesday, October 9, 2012, 3:31 PM
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
> ??
>
>
>
>
>
>
>
>
>
> All
> ?????????? I have a Tektronix 310 that the scope fades after about 15 minutes of being turned on. Any experience in this area would be appreciated. My guess is CRT? Not sure. Anyone?
>
|
Re: Tantalums cant take surges. (Subject was Aluminiumversus Tantalum Electrolytics)
The MANUFACTURER'S DATASHEETS I read specifically call out a small (10 ohm for example) series resistor to mitigate the tantalum's known inability to handle surges. Tek followed these guidelines.
The OTHER problems tantalums have with a short lifetime and a catastrophic failure mechanism, that we now know so well, probably did not become fully understood until years later after it was too late. That was not something Tek would become aware of until it was too late.
When tantalums first became available they had some great advantages. From an engineering perspective their size makes it possible to squeeze more functionality into a smaller space. Their cost makes them economically attractive and lowers instrument costs. What would you have done when presented with this new technology?
Dennis
toggle quoted message
Show quoted text
-----Original Message----- From: Chuck Harris [mailto:cfharris@...] Sent: Wednesday, October 10, 2012 5:20 AM I suspect that tek engineers didn't put the resistors and inductors before the tantalum capacitors to protect from surges, but rather to act as an input resistor to a simple RC filter.... the network was there because they wanted to clean up the power going to subassemblies. The fact that the small resistors and inductors acted as surge current limiters, and fuses was just a happy side benefit. Tek engineers used the tantalums just like everyone else did during that era, as small sized large value storage capacitors that had good HF characteristics. It wasn't until much later that the capacitor manufacturers started seeing surge related failures, and began to provide warnings about limiting surge currents. They never told you to limit working voltage to 1/2 the capacitor's rated voltage... that is something that NASA learned as it tried to qualify tantalums for space use. NASA learned about the voltage issues because one of their standard ways of qualifying parts was to run them at 2x their rated voltage, which in the case of a tantalum was a disaster. Even if the part survived the testing, it was damaged and set to fail under normal operation. -Chuck Harris Miroslav Pokorni wrote: Hello Dennis,
You said: "Tek engineers know this and design for it."
If that is so, how come that there are massive failures of tantalums
in 465, 7854 and other scopes.
On 10/9/2012 6:49 AM, Dennis Tillman wrote:
Tek engineers
know this and design for it.
|
Re: Bright dots at start of the trace on a 547
I see three different Tektronix part numbers for the 2N2207 which makes my suspect they were qualifying or grading them: 151-0063-00 Vcbo 70 Vceo 70 <--- Q184 151-0129-00 Vcbo 50 Vceo 50 151-0187-00 Vcbo 70 Vceo 50 With the BE junction reverse biased, Vcex which is even higher than Vcbo would apply but I could not find that specification for the 2N2207 which is not surprising since it is usually only specified for high voltage switching transistors. Operating with a reverse biased BE junction may explain why the 2N3906 substitution worked. On Wed, 10 Oct 2012 10:22:20 -0000, "Albert" <aodiversen@...> wrote: I got my data from the Tek cross reference which mentions 70 V for both Vceo and Vcbo.
BTW Just a curiosity, mentioned in 547 Notes: in ALT sweep mode Q184 goes in base-emitter breakdown when A is being displayed.
Albert
--- In TekScopes@..., David <davidwhess@...> wrote:
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.
|
Re: Tekronix 310 question
On 10/10/2012 06:37 AM, DiPaolo Richard wrote:
I do now need a service manual for a Tektronix 310!!!
|
Sergey Kubushyn
zenith5106
David Hess