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Re: [TCML] ocilloscope: Yep, I blew mine, too

1. you will find that a vacuum tube scope is much more tolerant of overvoltages with low current 2. you can make an HV resistor by putting many LV resistors in series - make your 100 meg (10 is way too low) resistor out of 100 1 meg resistors in series, put it in a plastic sleeve and fill sleeve with HV grease

From: <Davetracer@xxxxxxx>
Sent: Saturday, October 31, 2009 10:00 AM
To: <tesla@xxxxxxxxxx>
Subject: Re: [TCML] ocilloscope: Yep, I blew mine, too

Having blown an oscilloscope of mine looking at Tesla Coil waveforms, I
(learned from sad experience) would agree with Ed here that caution is in

I felt that having my scope many feet away and using a small wire as  the
pickup was "careful enough". And I was wrong.

You could perhaps limit the danger with an input resistor network, however,
you'd need resistors that will hold up under *extreme* voltages. (I have
no idea where you'd find them. Other people on this list do know, however.)

Something like this:   (I am so bad at drawing little schematics  with
ASCII art...) would help cut the input voltage by 10x. Changing R2 to 100K
would cut it on the order of 100x.

Probe "hot"
     \   R1  -- 10 Megohm
     + ----------> Scope Probe "In"
      \  R2    -- 1  Megohm
    Probe Ground ----> Scope Probe Ground  "In"

You can also do a capacitor network with resistor bypasses, but the drawing
for that would look just awful.

Another thing you can do is connect a simple ol' NE-2 neon light between
probe-hot and ground. If it goes on, there's more than ~~70 volts between hot
and ground, and that's really time to back off with the probe and triple
check,  and be certain you know what you're doing.

Other coilers have related stories of blowing various systems in their
houses (burglar alarms, garage door openers, and whatnot).

Never a dull moment with Tesla Coils! Oh, well, that's part of the  fun.


Dave Small

In a message dated 10/31/2009 9:57:04 A.M. Mountain Daylight Time,
evp@xxxxxxxxxxx writes:

G Hunter  wrote:

What's a wenherst generator?  Are you referring to a  Wimshurst
electrostatic machine? Please explain what you are trying to do. I don't have
enough information to understand your question, let  alone answer it.


Gregory R.  Hunter

If that's what you're talking about I wouldn't  get it anywhere near
a scope- possibility of high voltage discharge and  blowing up the input
to the  scope.


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