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Guest
Mon Mar 06, 2006 1:20 am
Joerg wrote:
Quote:
If you need a fast analog scope the best bet is to hunt for business
closure auctions (that's where I got a 1GHz HP) or other used equipment
sources.
Actually I regularly use high bandwidth analog & digital scopes at
work, so what I can do with my home gear aquired during my teenage
gears (and just reclaimed from parent's basement) is more curiosity
than necessity.
Speaking of deflection, I noticed there was a spot of something on the
scope screen, and grabbed a paper tissue to clean it. Talk about
electrostatic deflection!
Quote:
One very tough cookie would be the speed upgrade of the input
attenuator. This thing is rather complicated with all the little trim
caps and the fact that it is all jammed into very tight shielded spaces
doesn't make that job easier.
Yeah, I have that to look forward if I go ahead with the sampling scope
project I've been thinking about...
Michael A. Terrell
Guest
Mon Mar 06, 2006 4:15 pm
Joerg wrote:
Quote:
Hello Jim,
FYI,the CRT is a definite limit on bandwidth. The CRT electron gun
structure is VERY different between the 100Mhz TEK 465 and the 200-250Mhz
TEK 475 models. The 475 uses a distributed deflection plate assembly that
is terminated by a separate ceramic termination resistor network. Same goes
for the 500Mhz 7904 CRT.
True, but now you are talking about a whole different market, the
high-end. The OP just wanted to get past 5MHz and on those scopes it's
usually the amp that limits the BW. They often just couldn't afford
another buck or two in production for hotter final amp transistors when
the whole scope has to be under $250.
Case in point: I have used the plates of a scope CRT directly for
transmitter measurements. I could easily go to 30MHz with the CRT of a
scope that was otherwise tapering off at 10MHz (3db). With direct drive
there wasn't even one dB of slump in amplitude.
Regards, Joerg
http://www.analogconsultants.com
How about using the video driver ICs and output transistors from a
dead VGA monitor? Use a good op amp to invert the signal to one
channel.
--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.
Michael A. Terrell
Central Florida
Joerg
Guest
Mon Mar 06, 2006 11:08 pm
Hello Michael,
Quote:
How about using the video driver ICs and output transistors from a
dead VGA monitor? Use a good op amp to invert the signal to one
channel.
Sure. I think I mentioned video transistors before, they can be had for
even less than those from VGA monitors. However, on a scope that has to
retail for $250 even 10c more might not be in the cards because you need
two of them, or four if it's a 2-channel.
Personally I am cautious with TV chips such as video drivers. They
rpoduction lifetime may not be long and I have seen people get burned
big time by sudden parts obsolescence. Basically when they asked for
leadtime they were told "infinity".
Regards, Joerg
http://www.analogconsultants.com
Jim Yanik
Guest
Tue Mar 07, 2006 1:36 am
Joerg <notthisjoergsch_at_removethispacbell.net> wrote in
news:wfJOf.44881$H71.2482_at_newssvr13.news.prodigy.com:
Quote:
cs_posting_at_hotmail.com wrote:
It seems that in a cheap scope, the amplifier is the first limit, but
there's also a limit to what a basic CRT can do - to get really high
bandwidth you also need this transmission line plate structure.
Not if you just want to push your 20MHz scope a tad higher but certainly
when you want to reach VHF with it. I guess that is one of the reasons
why many older Tek scopes aren't repaired once the CRT goes kaputt. A
new CRT would often cost more than the residual market value of the
whole scope.
No,it's because those CRTs (all TEK-made;single-source) are no longer in
production,and no longer available. IOW,there are no "new CRT's".
IMO,if new CRTs were available,people would buy them despite costing more
than the present market value of the scope.
(assuming the rest of the scope was working or repairable.)
If you are VERY lucky,you can find an unused CRT that was stocked by the US
military and sold off as surplus.
(and TEK sold off their CRT unit,they no longer make -any- CRTs.)
--
Jim Yanik
jyanik
at
kua.net
Guest
Tue Mar 07, 2006 6:25 am
Jim Yanik wrote:
Quote:
No,it's because those CRTs (all TEK-made;single-source) are no longer in
production,and no longer available. IOW,there are no "new CRT's".
IMO,if new CRTs were available,people would buy them despite costing more
than the present market value of the scope.
(assuming the rest of the scope was working or repairable.)
Always thought glass blowing would be an interesting hobby...
More seriously, either someone in asia is making something comparable,
or there are no new high bandwidth analog scopes to be had at all?
My guess though is that affordable real time sampling either has, or
soon will surpass the bandwidth of affordable CRT's - at least on the
new market, and on the used market eventually.
Jim Yanik
Guest
Tue Mar 07, 2006 2:06 pm
cs_posting_at_hotmail.com wrote in
news:1141705507.107568.255990_at_z34g2000cwc.googlegroups.com:
Quote:
Jim Yanik wrote:
No,it's because those CRTs (all TEK-made;single-source) are no longer
in production,and no longer available. IOW,there are no "new CRT's".
IMO,if new CRTs were available,people would buy them despite costing
more than the present market value of the scope.
(assuming the rest of the scope was working or repairable.)
Always thought glass blowing would be an interesting hobby...
Actually,most TEK-made CRTs had a ceramic cast bell,gllued-on
faceplate(nice and FLAT),and just the neck tube was blown glass.
Only the early CRTs were all-glass.
Quote:
More seriously, either someone in asia is making something comparable,
or there are no new high bandwidth analog scopes to be had at all?
I don't know.I have not seen any references to high-BW analog scopes for
sale.
Quote:
My guess though is that affordable real time sampling either has, or
soon will surpass the bandwidth of affordable CRT's - at least on the
new market, and on the used market eventually.
It's FAR cheaper to use a LCD video display and digitizing circuitry than
to make a high bandwidth CRT for an analog scope;that's one problem.
Beware of used TEK TDS scopes,as they may be past the LTPS(long term
product support) period,and thus have NO parts or assemblies available,and
no schematics for troubleshooting.
--
Jim Yanik
jyanik
at
kua.net
Joerg
Guest
Tue Mar 07, 2006 9:10 pm
Hello Jim,
Quote:
I don't know.I have not seen any references to high-BW analog scopes for
sale.
OTOH there are still a lot of used one to be had a reasonable cost. Here
in the lab the trusty old 7704A is dutifully continuing its job.
Quote:
It's FAR cheaper to use a LCD video display and digitizing circuitry than
to make a high bandwidth CRT for an analog scope;that's one problem.
However, there are things you can't properly diagnose with an LCD
screen. Also, I found that even on EMI analyzers (!) there are LCDs that
produce an incredible racket above 30MHz. It's pathetic but once at a
client I had to place aluminum foil over the display, hit "store" and
then remove the foil to look at the spectrum. The only other option
would have been to find a larger space for 10m measurements and look at
the screen with binoculars (seriously, I have done that). This was never
the case with the older HP gear.
Quote:
Beware of used TEK TDS scopes,as they may be past the LTPS(long term
product support) period,and thus have NO parts or assemblies available,and
no schematics for troubleshooting.
Regards, Joerg
http://www.analogconsultants.com
Jim Yanik
Guest
Tue Mar 07, 2006 11:10 pm
Joerg <notthisjoergsch_at_removethispacbell.net> wrote in
news:REmPf.57075$dW3.8653_at_newssvr21.news.prodigy.com:
Quote:
Hello Jim,
I don't know.I have not seen any references to high-BW analog scopes
for sale.
OTOH there are still a lot of used one to be had a reasonable cost.
Here in the lab the trusty old 7704A is dutifully continuing its job.
Yes,I was saddened to see the 7000 series disappear.
(except for the 7500 models!)
They were potent,flexible scope platforms.
I too would much rather use an analog scope than a digital scope.
--
Jim Yanik
jyanik
at
kua.net
Joerg
Guest
Wed Mar 08, 2006 12:16 am
Hello Jim,
Quote:
Yes,I was saddened to see the 7000 series disappear.
(except for the 7500 models!)
They were potent,flexible scope platforms.
I too would much rather use an analog scope than a digital scope.
I even bought a cheap digital camera for the lab, to be able to document
the screen contents since there is no GPIB except for the really slow
7D20 digital module. Well, at least that beats the messy fumbling with
that instant film back in the 80's.
Regards, Joerg
http://www.analogconsultants.com
Guest
Thu Mar 23, 2006 6:32 pm
Jim Yanik wrote:
Quote:
Always thought glass blowing would be an interesting hobby...
Actually,most TEK-made CRTs had a ceramic cast bell,gllued-on
faceplate(nice and FLAT),and just the neck tube was blown glass.
Only the early CRTs were all-glass.
I wonder if that might actually make a hobbyist attempt at a custom CRT
more reasonable?
I would certainly be nice to be able to get in there and change things,
rather than have each attempt be a one-shot try.
Idle contemplation though... no space for such a project even if there
were time and funds.
Jim Yanik
Guest
Thu Mar 23, 2006 9:51 pm
cs_posting_at_hotmail.com wrote in
news:1143138772.558485.42070_at_u72g2000cwu.googlegroups.com:
Quote:
Jim Yanik wrote:
Always thought glass blowing would be an interesting hobby...
Actually,most TEK-made CRTs had a ceramic cast bell,glued-on
faceplate(nice and FLAT),and just the neck tube was blown glass.
The flat glass,glued-on faceplate also gave us the internal graticule.
Earlier CRTs had external faceplates,or bonded-on faceplates that sometimes
debonded or got bubbles underneath.
Quote:
Only the early CRTs were all-glass.
I wonder if that might actually make a hobbyist attempt at a custom CRT
more reasonable?
I dunno;it wasn't an easy task even for TEK,they had to trash batches of
CRTs,some lines had very high reject rates.The 2465 CRT was quite an
engineering feat with it's quadrupole lens that eliminated the mesh lens
and enabled a shorter CRT and still retain high BW capability,also
achieving low deflection sensitivity.
Quote:
I would certainly be nice to be able to get in there and change things,
rather than have each attempt be a one-shot try.
Uh,even TEK did not repair or alter ceramic-belled CRTs after they were
finished,evacuated and tested. They did break them up,and reuse the
electron gun/deflection structures,and recycled the faceplate glass.
(or they used "seconds" for internal TEK use;that's how I got a FREE new
CRT for my 2213!)
We had to return old CRTs to Beaverton for recycling.
Quote:
Idle contemplation though... no space for such a project even if there
were time and funds.
--
Jim Yanik
jyanik
at
kua.net
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