10ms timebase cap

C

Creamed_emu

Guest
Im restoring an old dual trace valve oscilloscope and after geting the set
functioning i have found there is no 10ms horozontal deflection. I found
that cap that is short circuit. it is an old clear plastic/foil cap. the
problem is part of it has melted, the part with the value on it. all that is
there is ***,000p and 669 written under it. Does anyone know the value of a
10ms cap that belongs there? i dont have the schematic. I was thinking mabey
if it used the same resistor for the rc oscillator (that is how it works?) i
could compare the cap values of other scan rates. i believe the 10us uses
190pf and the 1us uses 360 pf. is there any way to find the value of the
missing cap? This scope has an enormous CRT in it and becuase it is designed
with valves, its virturally indestructable - Perfect for a beginner like me.

Anyway, thanks for any help you can offer - Ben
 
"Creamed_emu" <shazzy@iprimus.com.au> wrote in message
news:401ef69e$1_1@news.iprimus.com.au...
Im restoring an old dual trace valve oscilloscope and after geting the set
functioning i have found there is no 10ms horozontal deflection. I found
that cap that is short circuit. it is an old clear plastic/foil cap. the
problem is part of it has melted, the part with the value on it. all that
is
there is ***,000p and 669 written under it. Does anyone know the value of
a
10ms cap that belongs there? i dont have the schematic. I was thinking
mabey
if it used the same resistor for the rc oscillator (that is how it works?)
i
could compare the cap values of other scan rates. i believe the 10us uses
190pf and the 1us uses 360 pf. is there any way to find the value of the
missing cap? This scope has an enormous CRT in it and becuase it is
designed
with valves, its virturally indestructable - Perfect for a beginner like
me.

Anyway, thanks for any help you can offer - Ben


Ben
Click to expand...
It would be helpful if you tell us the make and model of the 'scope.
Martin.

--
martin<dot here>whybrow<at here>ntlworld<dot here>com
 
"Creamed_emu" <shazzy@iprimus.com.au> wrote in
news:401ef69e$1_1@news.iprimus.com.au:

Im restoring an old dual trace valve oscilloscope and after geting the
set functioning i have found there is no 10ms horozontal deflection. I
found that cap that is short circuit. it is an old clear plastic/foil
cap. the problem is part of it has melted, the part with the value on
it. all that is there is ***,000p and 669 written under it. Does
anyone know the value of a 10ms cap that belongs there? i dont have
the schematic. I was thinking mabey if it used the same resistor for
the rc oscillator (that is how it works?) i could compare the cap
values of other scan rates. i believe the 10us uses 190pf and the 1us
uses 360 pf. is there any way to find the value of the missing cap?
This scope has an enormous CRT in it and becuase it is designed with
valves, its virturally indestructable - Perfect for a beginner like
me.

Anyway, thanks for any help you can offer - Ben
Click to expand...
Check the other timing caps,the unknown cap should be a decade multiple of
the rest of them,and then using resistors for the 1,2,5 submultiples. They
were selected and sold as matched sets,and there were letter codes to
indicate the selection groups,like +C,-A,etc.(for TEK scopes) Maybe
10,000pf? For that slow a range,it would have to be fairly large,more in
the uF range,IMO.

669 may be a date code.

It would also help if you mentioned the make and model of the scope.
Perhaps a TEK 500 series?

The sweeps are generated with a gated Miller integrator(ramp generator),not
an oscillator.(at least in a TEK scope.)

--
Jim Yanik
jyanik-at-kua.net
 
Creamed_emu wrote:
Im restoring an old dual trace valve oscilloscope and after geting the set
functioning i have found there is no 10ms horozontal deflection. I found
that cap that is short circuit. it is an old clear plastic/foil cap. the
problem is part of it has melted, the part with the value on it. all that is
there is ***,000p and 669 written under it. Does anyone know the value of a
10ms cap that belongs there? i dont have the schematic. I was thinking mabey
if it used the same resistor for the rc oscillator (that is how it works?) i
could compare the cap values of other scan rates. i believe the 10us uses
190pf and the 1us uses 360 pf. is there any way to find the value of the
missing cap? This scope has an enormous CRT in it and becuase it is designed
with valves, its virturally indestructable - Perfect for a beginner like me.

Anyway, thanks for any help you can offer - Ben
Click to expand...
Good thing that every scope ever made used the same cap.
That way you don't have to disclose the model.
Absent any possiblilty of getting relevant information,
maybe you should just
stick in a cap and measure the sweep speed. Shouldn't take more
than two tries to plot the graph and determine the correct value.
If you care about the calibration, it's unlikely that you'll be able
to buy a (single) stock cap close enough.
mike

--
Return address is VALID.
Bunch of stuff For Sale and Wanted at the link below.
Toshiba & Compaq LiIon Batteries, Test Equipment
Honda CB-125S $800 in PDX
TEK Sampling Sweep Plugin and RM564
Tek 2465 $800, ham radio, 30pS pulser
Tektronix Concept Books, spot welding head...
http://www.geocities.com/SiliconValley/Monitor/4710/
 
And it's pretty easy to try one with an adequate voltage rating and
extrapolate from there. :)

--- sam | Sci.Electronics.Repair FAQ Home Page: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
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Important: The email address in this message header may no longer work. To
contact me, please use the feedback form on the S.E.R FAQ Web sites.



Jim Yanik <jyanik@abuse.gov> writes:

"Creamed_emu" <shazzy@iprimus.com.au> wrote in
news:401ef69e$1_1@news.iprimus.com.au:

Im restoring an old dual trace valve oscilloscope and after geting the
set functioning i have found there is no 10ms horozontal deflection. I
found that cap that is short circuit. it is an old clear plastic/foil
cap. the problem is part of it has melted, the part with the value on
it. all that is there is ***,000p and 669 written under it. Does
anyone know the value of a 10ms cap that belongs there? i dont have
the schematic. I was thinking mabey if it used the same resistor for
the rc oscillator (that is how it works?) i could compare the cap
values of other scan rates. i believe the 10us uses 190pf and the 1us
uses 360 pf. is there any way to find the value of the missing cap?
This scope has an enormous CRT in it and becuase it is designed with
valves, its virturally indestructable - Perfect for a beginner like
me.

Anyway, thanks for any help you can offer - Ben




Check the other timing caps,the unknown cap should be a decade multiple of
the rest of them,and then using resistors for the 1,2,5 submultiples. They
were selected and sold as matched sets,and there were letter codes to
indicate the selection groups,like +C,-A,etc.(for TEK scopes) Maybe
10,000pf? For that slow a range,it would have to be fairly large,more in
the uF range,IMO.

669 may be a date code.

It would also help if you mentioned the make and model of the scope.
Perhaps a TEK 500 series?

The sweeps are generated with a gated Miller integrator(ramp generator),not
an oscillator.(at least in a TEK scope.)

--
Jim Yanik
jyanik-at-kua.net
Click to expand...
 
mike <spamme0@juno.com> wrote in news:401F16B0.4010100@juno.com:



maybe you should just
stick in a cap and measure the sweep speed. Shouldn't take more
than two tries to plot the graph and determine the correct value.
If you care about the calibration, it's unlikely that you'll be able
to buy a (single) stock cap close enough.
mike
Click to expand...
Well,he could parallel caps to trim it to spec,given a reliable cal
source.I've seen that done in TEK 500 series scopes.

--
Jim Yanik
jyanik-at-kua.net
 
Jim Yanik wrote:
mike <spamme0@juno.com> wrote in news:401F16B0.4010100@juno.com:




maybe you should just
stick in a cap and measure the sweep speed. Shouldn't take more
than two tries to plot the graph and determine the correct value.
If you care about the calibration, it's unlikely that you'll be able
to buy a (single) stock cap close enough.
mike



Well,he could parallel caps to trim it to spec,given a reliable cal
source.I've seen that done in TEK 500 series scopes.
Click to expand...
Hence the use of the word (single)...
My point is that knowing the number printed on the cap won't necessarily
solve the problem.
mike

--
Return address is VALID.
Bunch of stuff For Sale and Wanted at the link below.
Toshiba & Compaq LiIon Batteries, Test Equipment
Honda CB-125S $800 in PDX
TEK Sampling Sweep Plugin and RM564
Tek 2465 $800, ham radio, 30pS pulser
Tektronix Concept Books, spot welding head...
http://www.geocities.com/SiliconValley/Monitor/4710/
 
"Creamed_emu" bravely wrote to "All" (03 Feb 04 12:05:12)
--- on the heady topic of "10ms timebase cap"

It doesn't make sense that a longer timebase uses a smaller value cap.
Make/model missing, etc...

Cr> From: "Creamed_emu" <shazzy@iprimus.com.au>

Cr> Im restoring an old dual trace valve oscilloscope and after geting the
Cr> set functioning i have found there is no 10ms horozontal deflection. I
Cr> found that cap that is short circuit. it is an old clear plastic/foil
Cr> cap. the problem is part of it has melted, the part with the value on
Cr> it. all that is there is ***,000p and 669 written under it. Does anyone
Cr> know the value of a 10ms cap that belongs there? i dont have the
Cr> schematic. I was thinking mabey if it used the same resistor for the rc
Cr> oscillator (that is how it works?) i could compare the cap values of
Cr> other scan rates. i believe the 10us uses 190pf and the 1us uses 360
Cr> pf. is there any way to find the value of the missing cap?
 
mike <spamme0@juno.com> wrote in news:4020C398.7020605@juno.com:

Jim Yanik wrote:
mike <spamme0@juno.com> wrote in news:401F16B0.4010100@juno.com:




maybe you should just
stick in a cap and measure the sweep speed. Shouldn't take more
than two tries to plot the graph and determine the correct value.
If you care about the calibration, it's unlikely that you'll be able
to buy a (single) stock cap close enough.
mike



Well,he could parallel caps to trim it to spec,given a reliable cal
source.I've seen that done in TEK 500 series scopes.


Hence the use of the word (single)...
My point is that knowing the number printed on the cap won't necessarily
solve the problem.
mike
Click to expand...
TEK's timebase caps were *standard values* that were matched to eliminate
tolerance deviations.Knowing the original value would be a great help.

--
Jim Yanik
jyanik-at-kua.net
 
Jim Yanik wrote:
mike <spamme0@juno.com> wrote in news:4020C398.7020605@juno.com:


Jim Yanik wrote:

mike <spamme0@juno.com> wrote in news:401F16B0.4010100@juno.com:





maybe you should just
stick in a cap and measure the sweep speed. Shouldn't take more
than two tries to plot the graph and determine the correct value.
If you care about the calibration, it's unlikely that you'll be able
to buy a (single) stock cap close enough.
mike



Well,he could parallel caps to trim it to spec,given a reliable cal
source.I've seen that done in TEK 500 series scopes.


Hence the use of the word (single)...
My point is that knowing the number printed on the cap won't necessarily
solve the problem.
mike



TEK's timebase caps were *standard values* that were matched to eliminate
tolerance deviations.
Click to expand...
I'm in a mood to rattle your cage so I'll ask, "Isn't "matched"
the very definition of "non-standard"???? ;-)

Knowing the original value would be a great help.
Click to expand...
Since the OP refused to give any clues about the scope in question,
that's not possible.

I'm really RANTING about people who ask questions
with insufficient specificity to allow ANY useful information to be
provided.
Unless you have the Psychic Hotline on speed dial, you ain't gonna
be able to answer the question.

If the OP had merely mentioned the make/model, (and it was a TEK), you
or any number of us could have given the value, part number, cautions on
cap type and Deane Kidd's phone number to get one.

As for "great"...well...to make this work, you're still gonna have to
stick in a cap, measure the sweep speed and either parallel another cap
or find one closer to the short end of the tolerance that can be
paralleled up to the needed value. Knowing the start value would save
a step in the experiment...but that would save less time than the OP
spent (not) asking the question. Don't get me started on cap
construction, temperature sensitivity, dielectric absorption...and the
zillion other things one might want to think about to match the other
caps and compensation in the system.

mike



--
Return address is VALID.
Bunch of stuff For Sale and Wanted at the link below.
Toshiba & Compaq LiIon Batteries, Test Equipment
Honda CB-125S $800 in PDX
TEK Sampling Sweep Plugin and RM564
Tek 2465 $800, ham radio, 30pS pulser
Tektronix Concept Books, spot welding head...
http://www.geocities.com/SiliconValley/Monitor/4710/
 
mike <spamme0@juno.com> wrote in news:4021A6C3.1030901@juno.com:

Jim Yanik wrote:
mike <spamme0@juno.com> wrote in news:4020C398.7020605@juno.com:


Jim Yanik wrote:

mike <spamme0@juno.com> wrote in news:401F16B0.4010100@juno.com:





maybe you should just
stick in a cap and measure the sweep speed. Shouldn't take more
than two tries to plot the graph and determine the correct value.
If you care about the calibration, it's unlikely that you'll be
able to buy a (single) stock cap close enough.
mike



Well,he could parallel caps to trim it to spec,given a reliable cal
source.I've seen that done in TEK 500 series scopes.


Hence the use of the word (single)...
My point is that knowing the number printed on the cap won't
necessarily solve the problem.
mike



TEK's timebase caps were *standard values* that were matched to
eliminate tolerance deviations.

I'm in a mood to rattle your cage so I'll ask, "Isn't "matched"
the very definition of "non-standard"???? ;-)
Click to expand...
No."matched" is *selected* standard caps,like picking the caps (out of a
big bin of them)that are -5% of *marked value*,then picking the ones that
are +3%,and using them with other caps of the next decade standard value of
the SAME deviation,-5% with -5%,+3% with +3%,until you get a -matched-
SET.But the values are the standard ones the manufacturer has.
Like the ones listed in Digi-Key,where the chart says "standard values".
(like .033uf,330pf,.1uf,10uf,etc)

Knowing the original value would be a great help.

Since the OP refused to give any clues about the scope in question,
that's not possible.

I'm really RANTING about people who ask questions
with insufficient specificity to allow ANY useful information to be
provided.
Unless you have the Psychic Hotline on speed dial, you ain't gonna
be able to answer the question.

If the OP had merely mentioned the make/model, (and it was a TEK), you
or any number of us could have given the value, part number, cautions
on cap type and Deane Kidd's phone number to get one.

As for "great"...well...to make this work, you're still gonna have to
stick in a cap, measure the sweep speed and either parallel another
cap or find one closer to the short end of the tolerance that can be
paralleled up to the needed value. Knowing the start value would save
a step in the experiment...but that would save less time than the OP
spent (not) asking the question. Don't get me started on cap
construction, temperature sensitivity, dielectric absorption...and the
zillion other things one might want to think about to match the other
caps and compensation in the system.

mike
Click to expand...
Sure,you want to use polypropylene caps or silver mica depending on the
value needed.If you can't get those,then polystyrene.But considering most
scope timebases are only 3% accurate,that's good enough.

BTW,I worked for TEK for 21.5 years as a scope/instrument repair and cal
tech;Indianapolis and Orlando Field offices.

--
Jim Yanik
jyanik-at-kua.net
 
Jim Yanik wrote:
mike <spamme0@juno.com> wrote in news:4021A6C3.1030901@juno.com:


Jim Yanik wrote:

mike <spamme0@juno.com> wrote in news:4020C398.7020605@juno.com:



Jim Yanik wrote:


mike <spamme0@juno.com> wrote in news:401F16B0.4010100@juno.com:






maybe you should just
stick in a cap and measure the sweep speed. Shouldn't take more
than two tries to plot the graph and determine the correct value.
If you care about the calibration, it's unlikely that you'll be
able to buy a (single) stock cap close enough.
mike



Well,he could parallel caps to trim it to spec,given a reliable cal
source.I've seen that done in TEK 500 series scopes.


Hence the use of the word (single)...
My point is that knowing the number printed on the cap won't
necessarily solve the problem.
mike



TEK's timebase caps were *standard values* that were matched to
eliminate tolerance deviations.

I'm in a mood to rattle your cage so I'll ask, "Isn't "matched"
the very definition of "non-standard"???? ;-)



No."matched" is *selected* standard caps,like picking the caps (out of a
big bin of them)that are -5% of *marked value*,then picking the ones that
are +3%,and using them with other caps of the next decade standard value of
the SAME deviation,-5% with -5%,+3% with +3%,until you get a -matched-
SET.But the values are the standard ones the manufacturer has.
Like the ones listed in Digi-Key,where the chart says "standard values".
(like .033uf,330pf,.1uf,10uf,etc)


Knowing the original value would be a great help.

Since the OP refused to give any clues about the scope in question,
that's not possible.

I'm really RANTING about people who ask questions
with insufficient specificity to allow ANY useful information to be
provided.
Unless you have the Psychic Hotline on speed dial, you ain't gonna
be able to answer the question.

If the OP had merely mentioned the make/model, (and it was a TEK), you
or any number of us could have given the value, part number, cautions
on cap type and Deane Kidd's phone number to get one.

As for "great"...well...to make this work, you're still gonna have to
stick in a cap, measure the sweep speed and either parallel another
cap or find one closer to the short end of the tolerance that can be
paralleled up to the needed value. Knowing the start value would save
a step in the experiment...but that would save less time than the OP
spent (not) asking the question. Don't get me started on cap
construction, temperature sensitivity, dielectric absorption...and the
zillion other things one might want to think about to match the other
caps and compensation in the system.

mike





Sure,you want to use polypropylene caps or silver mica depending on the
value needed.If you can't get those,then polystyrene.But considering most
scope timebases are only 3% accurate,that's good enough.
Click to expand...
My statement was that it's unlikely you can go buy a cap that will plug
right in and be (specified in such a way that the sweep will be)
calibrated. Even if you got the exact valaue, it's not guaranteed that the
other caps in the matched set would be within 3% of nominal.
Of course, there's always random luck.
I understand we're arguing semantics, but that's why arguments were
invented.

BTW,I worked for TEK for 21.5 years as a scope/instrument repair and cal
tech;Indianapolis and Orlando Field offices.
Click to expand...
Congratulations. You got me beat. I only spent 20 years at
TEK Beaverton as a design engineer.
mike



--
Return address is VALID.
Bunch of stuff For Sale and Wanted at the link below.
Toshiba & Compaq LiIon Batteries, Test Equipment
Honda CB-125S $800 in PDX
TEK Sampling Sweep Plugin and RM564
Tek 2465 $800, ham radio, 30pS pulser
Tektronix Concept Books, spot welding head...
http://www.geocities.com/SiliconValley/Monitor/4710/
 
mike <spamme0@juno.com> wrote in news:4022EE82.2080005@juno.com:

Jim Yanik wrote:
Click to expand...

BTW,I worked for TEK for 21.5 years as a scope/instrument repair and
cal tech;Indianapolis and Orlando Field offices.

Congratulations. You got me beat. I only spent 20 years at
TEK Beaverton as a design engineer.
mike
Click to expand...
I agree that it's unlikely to plug in a single cap and have it within
tolerance for the scope. (Although I used to do it at TEK,on 200 series
miniscopes.)

What products did you work on?

--
Jim Yanik
jyanik-at-kua.net
 
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