Re: O-Scope for tesla coil use

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Terry Fritz <teslalist@xxxxxxxxxxxxxxxxxxxxxxx>

Hi Stork,

I think you mean like this:

http://hot-streamer.com/temp/DiffProbe01.gif

See the files at:

http://hot-streamer.com/temp

Starting with "diffprobe".

Protecting the scope from faults is a big deal.  See this one which is more 
safe:

http://hot-streamer.com/temp/DiffProbe03.gif

http://hot-streamer.com/temp/DiffProbe21.gif

I would not bother trying to use other than a simple battery powered low 
bandwidth TL082 circuit.  I did manage to get the fast TI chip to sort of 
work but it was a real mess.  Not worth it...  Best to keep it simple.

The problem is the high impedances at high voltage and high bandwidth 
require compensations circuits that normal humans just can't figure 
out.  If it was easy, Tek would not get $1000+ for the darn 
things...  There are nice high sped op amps out there, but soldering in 
countless little 1pF chips all over the place to pull the signals in is 
just about impossible.  You pretty much need the Tek probe to guide you 
anyway.  Then, the next time you try it everything is different so you 
start from scratch again.  Not repeatable at all...   So if the simple 
TL082 one will work, your all set,  if you need like 50MHz stuff, you just 
have to buy the darn things.

Cheers,

        Terry


At 10:56 AM 3/23/2005, you wrote:
> Terry,
>
> Back in 2003 you had a thread going about a differential wideband HF 
> amplifier based on the TL082 quad Jfet op-amp.  I remember Malcolm 
> responding.  I cannot find the thread now though.  How did the project 
> turn out?  Do you have a design/schematic?
>
> A plug in differential amp for older tube scopes is cheaper, but confined 
> to that tube scope.   A stand alone fet differential amp is much more 
> versatile, but much more $$$.
>
> I have long felt a stand alone fet differental op-amp PCB would be a good 
> project.  Maybe I can revive it.
>
> Our higher voltage DC voltage regulator PCB is progressing.  Hopefully, 
> I'll be able to post the schematic.
>
> stork