[sdiy] Old 20Mhz scope high on LSD!!

[karl dalen]

 --- harrybissell <harrybissell at prodigy.net> skrev: 
> Hi Karl (inline)

OK then if i lower my hopings then what about 50Mhz?

Anything better then 20 Mhz then.........25Mhz!!! 
I hate to have a working but semi strangled device here wich i can semi use!!

Reg
KD

Ps: Cartman paid 5 usd for the pubes! :-)
 
> > > Of course you are correct... there are a few problems
> > > 1) The phosphor of the scope tube will have been selected for the sweep
> > > speed.  Higher sweep rates will need a shorter persistance phosphor, and
> > > a lot higher acceleration voltage for the tube.
> >
> > My friend says that he had looked at two old Hitachi scopes, one 20Mhz
> > the other was a 100Mhz, both used the same type of CRT tube, so that
> > contradicts you sugestion of shorter persistance phosphor and higher
> > acc voltage! Im not saying that you are wrong, my frind might have
> > missed some issues.But explain the effect of "persistance phosphor"?
> 
> A faster scope must have a shorter persistance phosphor, or it will display
> a big fuzzy blur from sucessive traces still on the screen.
> 
> Writing that short persistance phosphor takes more energy (ie higher voltage)
> to get the picture on the screen in the shorter time allowed...
> 
> Hitachi might have used the faster tube on a slower scope... but you can't
> take
> the slower tube up to faster speeds (at least not with guaranteed success...)
> 
> > Btw, I did a quick search on the net and found:
> > http://members.tripod.com/michaelgellis/scope.html
> >
> > Wich also speaks about BW's about 100Mhz!!
> >
> > > 2)  The high voltage deflection amps need to be beefed up to handle the
> > > faster signals, at high voltages.
> >
> > My schemos says that they uses high voltage but almost no current at +150V.
> > Why would i need to beef up them for higher voltage when it is the Bw thats
> > going to be expanded. Explain please!!
> 
> not higher voltages. AT high voltages.  The voltages will be the same (and
> high)
> 
> but what seemed to be an acceptable waveshape at 20MHz will be very sloppy
> at 100MHz.  The problem is in the rise times and overshoot control.  The
> 20MHz
> signals will be almost like sine waves by comparison...
> 
> > If the BW are allready high for the defelections amps and it is the
> > input amp who limits BW, wich seams resonably build whise, why not try!
> > I dont see why the voltage should be higher?
> >
> > > 3) Damping everything properly will be tough, stray capacitances that
> > > were  not designed out of the chassis will come to haunt you in spooky
> > > LSD way.
> >
> > Damping, well exactly where would damping cause problems and why would
> > anyone inwolve the chassis otherwhise then using it as usual gnd!
> > I men if one looks at this scope update as RF design (with a little
> > higher voltages used) then i think its quite possibly!
> 
> as another post pointed out... the parasitic components are part of the
> circuit
> at 100MHz
> and were probably ignored at 20MHz, That was my point...
> 
> > > One possible solution would be
> > > to build a digital sampling front end and use the slow scope to read out
> > > the results.
> >
> > Thas much more expencive and cumbersome!
> 
> That would be my first choice though... you can get good fast A/D converters
> etc...
> of course it will be tough unless you already HAVE a good fast scope  :^P
> 
> > > I would recommend finding a broken scope of high bandwidth and restoring
> > > it if you > really want to play.
> >
> > I want to play, with my own scope, where im located i would
> > have to hunt for ages to find a faulty scope to play with.
> >
> > Aaarrrgghhhhh!!!
> >
> > You bastards,telling me its to difficult..... i wont give up
> !.......notyet!
> >
> > I will put pubes in your cilliconcarne!
> 
> That will be one spicy chili.  BTW I get these e-mails promising they will
> make
> me hard but thats no problem for me. Where can I get something to make me
> soft
> ???  <bfg>
> 
> H^) harry
> 
>