Scope bandwidth limitation - amp or crt?

[Jim Yanik]

[email protected] wrote in

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.

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.

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.

 

[Joerg]

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.

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.

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

 

[Jim Yanik]

Hello Jim,


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.

 

[Joerg]

Hello Jim,

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

 

[[email protected]]

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]

[email protected] wrote in

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.

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.

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.