[AMRadio] Be carefull with your scope!

[Mark Foltarz]

 I use an old HV divider probe such as the type used
on VTVMs. These probes were intended  for measuring
the 2nd anode voltage on TV sets. I found one for $3
at some ham fest.

 Essentially the probe is a 1000:1 divider with a 1m
ohm output impedance. It looks like a prop from a Buck
Rogers film. 

The arangement  Gives me about a 15KV headroom. Nice
for checking  B+ sag  or ripple on 2KV lines etc.

And no I have not attempted to do a phase correction
on the probe. I'll leave that to someone else.

DE KA4JVY
Mark



--- "Phil (VA3UX)" <phil at vaxxine.com> wrote:
> That really is a good reminder Mark. A few weeks ago
> I was reading mail on 
> a guitar amp list that I'm on and one of the guys
> was talking about 
> measuring B+ ripple with a scope on his 550V supply.
> The scope input 
> voltage rating thing occured to me so I mentioned on
> the list to be sure 
> the scope input and probe were rated for that
> voltage. The response was 
> like a deer staring into the headlights : "Huh?
> Theres a voltage rating on 
> this stuff ? ". Well he did know there was but he
> hadn't used his scope for 
> a couple of years and he had competley forgotten
> about it.  No damage was 
> done but he was lucky.
> 
> It's one thing to toast an old $50 service grade
> scope but it's a different 
> thing to hurt an HP 17xx series scope. "Needs
> repair" scopes in the HP 1700 
> series come up for auction quite often on eBay. If
> you can't get the parts, 
> consider buying a parts unit.
> 
> Thanks
> 
> Phil
> 
> At 10:22 PM 2/18/2002 -0500, you wrote:
> >Just a word of warning from someone that learned a
> lesson the hard way.
> >I was working on my Apache with my 275Mhz HP scope
> and after many
> >years of working on solid state gear, forgot that
> the scope has a Max.
> >input voltage limit. I totally trashed one input
> channel on a scope that was
> >
> >working well! Sure had a long talk with myself
> after that!
> >
> >Hope this may help others avoid this pitfall!
> >
> >Mark W1MJG
> >
> >
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