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

[karl dalen]

 --- harrybissell <harrybissell at prodigy.net> skrev: 
> KD on LSD ???    :^P

Hmm, whats that pink elephant doing up there in the sealing?
 
> 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"?

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!! 

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!   
 
> 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!
> 
> 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!

(im pressionating Cartman).:-)

Reg
KD