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Does the CRT deflection coil hold enough charge to zap somebody?

N

Nicole Bischoff

Jan 1, 1970
0
Richard the St00pid Bullis says so on 24hoursupport.helpdesk.
 
J

James Beck

Jan 1, 1970
0
Richard the St00pid Bullis says so on 24hoursupport.helpdesk.
Once, and I repeat ONCE, I pulled the connector for the deflection coils
on an Electrohome G-07 RGB monitor THEN discharged the anode. That will
wake you up when you grab the deflection coil connector. :)
One of those DUH moments.
 
F

Franc Zabkar

Jan 1, 1970
0
Richard the St00pid Bullis says so on 24hoursupport.helpdesk.

A coil holds no charge. A capacitor does. However a coil's back emf
may belt you if you interrupt its current flow.

- Franc Zabkar
 
B

Bill

Jan 1, 1970
0
Franc said:
A coil holds no charge. A capacitor does. However a coil's back emf
may belt you if you interrupt its current flow.

- Franc Zabkar
If the set is on and you are playing near the CRT you will get zapped
from the CRT and not the coil. If it is off you can get nailed by the 25
KV of the anode capacitance which can be there for days. I got knocked
across the room once by a hand to foot discharge, some people get killed
by it, and I now put my elbow on the chassis so only my arm gets hit, a
big ouch but not dangerous except to your arm and finger nerves.
Always discharge high voltage. I got nailed by a 2,000 volt capacitor on
a microwave that had been off for 3 days, less voltage but a big uF cap.
Bill Baka
 
H

hr(bob) [email protected]

Jan 1, 1970
0
  If the set is on and you are playing near the CRT you will get zapped
from the CRT and not the coil. If it is off you can get nailed by the 25
KV of the anode capacitance which can be there for days. I got knocked
across the room once by a hand to foot discharge, some people get killed
by it, and I now put my elbow on the chassis so only my arm gets hit, a
big ouch but not dangerous except to your arm and finger nerves.
Always discharge high voltage. I got nailed by a 2,000 volt capacitor on
a microwave that had been off for 3 days, less voltage but a big uF cap.
Bill Baka

Don't just discharge the anode one time, do it once, wait about 20
seconds and do a second discharge. There is a phenomenon that I can't
recall where the charge is stored partially in the glass envelope and
the voltage can rebuild up to a few kV after the initial discharge
unless the initial short lasts for several seconds.

Bob Hofmann
 
A

Arfa Daily

Jan 1, 1970
0
If the set is on and you are playing near the CRT you will get zapped
from the CRT and not the coil. If it is off you can get nailed by the 25
KV of the anode capacitance which can be there for days. I got knocked
across the room once by a hand to foot discharge, some people get killed
by it, and I now put my elbow on the chassis so only my arm gets hit, a
big ouch but not dangerous except to your arm and finger nerves.
Always discharge high voltage. I got nailed by a 2,000 volt capacitor on
a microwave that had been off for 3 days, less voltage but a big uF cap.
Bill Baka

Don't just discharge the anode one time, do it once, wait about 20
seconds and do a second discharge. There is a phenomenon that I can't
recall where the charge is stored partially in the glass envelope and
the voltage can rebuild up to a few kV after the initial discharge
unless the initial short lasts for several seconds.

Bob Hofmann


I was taught that it is because the area of the effective capacitor formed
by the internal anode coating, the glass, and the external coating, is so
large compared to the single small discharge point, that much of the
residual charge sort of 'rushes away' as far as it can to try to re-eqaulise
itself into an evenly distributed high voltage. Then, over a couple of
minutes, it spreads out again over the whole internal surface of the tube.
If you discharge over a couple of minutes with a resistive probe, you don't
get a problem.

Back in the days, I had an old anode lead cut from a scrap FBT, that fed
into a small plastic box that had a number of 10k resistors in it, in series
to up the overall voltage rating of them. Coming out of the other end, was a
lead with a croc clip on it. You used to just hook this to the external
coating grounding spring, and then plug the cavity connector into the tube.
Then go for a cup of coffee. When you came back, the tube could then be
dealt with in complete safety, including removing it for replacement.

Arfa
 
Don't just discharge the anode one time, do it once, wait about 20
seconds and do a second discharge. There is a phenomenon that I can't
recall where the charge is stored partially in the glass envelope and
thevoltagecan rebuild up to a few kV after the initial discharge
unless the initial short lasts for several seconds.

Bob Hofmann

I was taught that it is because the area of the effective capacitor formed
by the internal anode coating, the glass, and the external coating, is so
large compared to the single small discharge point, that much of the
residual charge sort of 'rushes away' as far as it can to try to re-eqaulise
itself into an evenly distributedhighvoltage. Then, over a couple of
minutes, it spreads out again over the whole internal surface of the tube..
If you discharge over a couple of minutes with a resistive probe, you don't
get a problem.

Back in the days, I had an old anode lead cut from a scrap FBT, that fed
into a small plastic box that had a number of 10k resistors in it, in series
to up the overallvoltagerating of them. Coming out of the other end, was a
lead with a croc clip on it. You used to just hook this to the external
coating grounding spring, and then plug the cavity connector into the tube.
Then go for a cup of coffee. When you came back, the tube could then be
dealt with in complete safety, including removing it for replacement.

Arfa- Hide quoted text -

- Show quoted text -

High voltage capacitors can even build up a charge just from
handling. Thats why high quality high voltage capacitors are shipped
with a shorting wire across the terminals. I've seen cases where
stock room personnel got zapped by high voltage capacitors that did
not have shorting wires. That's why I keep shorting wires on HV
capacitors, and discharge any capacitors that do not have them.

There are a few interesting stories regarding shocks from TV's and
other high voltage equipment at http://www.highvoltageinfo.com/whitepapers/high-voltage-stories.php
 
B

Bill

Jan 1, 1970
0
hr(bob) [email protected] said:
Don't just discharge the anode one time, do it once, wait about 20
seconds and do a second discharge. There is a phenomenon that I can't
recall where the charge is stored partially in the glass envelope and
the voltage can rebuild up to a few kV after the initial discharge
unless the initial short lasts for several seconds.

Bob Hofmann

Even with high quality instrumentation caps there is a memory effect
with some of them. Read some of Bob Pease's stuff in Electronic Design
and he has some stories about that. I'm an old analogue guy like him and
just when I think I've seen it all something new comes along.
Some Mylar caps are super low leakage but have a memory effect due to
residual electrons finding their way, as do many other types. Ceramic
are pretty good but not ideal, and since there are over 20-30 types,
glass included, I can't begin to tell you how many circuits that looked
good on the schematic didn't make it because of a cap problem.
A glass CRT was never intended to hold much charge beyond that required
not to fade at the end of a scan line before the next flyback pulse
recharged it again.
What Bob said above is still very true.
Bill Baka
 
Z

z

Jan 1, 1970
0
  If the set is on and you are playing near the CRT you will get zapped
from the CRT and not the coil. If it is off you can get nailed by the 25
KV of the anode capacitance which can be there for days. I got knocked
across the room once by a hand to foot discharge, some people get killed
by it, and I now put my elbow on the chassis so only my arm gets hit, a
big ouch but not dangerous except to your arm and finger nerves.
Always discharge high voltage. I got nailed by a 2,000 volt capacitor on
a microwave that had been off for 3 days, less voltage but a big uF cap.
Bill Baka

i still remember grabbing hold of the capacitor on my friend's science
fair project tesla coil when it was off. yahoohooie!! i felt like a
character in a warner brother's cartoon.
 
C

ChrisCoaster

Jan 1, 1970
0
i still remember grabbing hold of the capacitor on my friend's science
fair project tesla coil when it was off. yahoohooie!! i felt like a
character in a warner brother's cartoon.- Hide quoted text -

- Show quoted text -
____________________
Get a loada this. I was succesfully able to drill a pinhole into the
picture end of a 20" cathode tube, thus eVACUating it. I then
carefully broke off the neck, containing the electron guns. Now
realize that this neck is still fully intact and connected to the
motherboard of the TV.

So using a very long set of grilling tongs for gripping hotdogs, with
rubber-gloved left hand, and with my right hand turned on the TV at
the moment Brian Williams is "thanking us all for watching" NBC
nightly news.......











After a brief shower of red, green, and blue sparks and a lot of loud
crackling, Brian Williams' FACE is now permanently etched on my
ceiling! A little trapezoidally stretched, but it is him - of that
I'm certain.

-CC
 
B

boardjunkie

Jan 1, 1970
0
Once, and I repeat ONCE, I pulled the connector for the deflection coils
on an Electrohome G-07 RGB monitor THEN discharged the anode.  That will
wake you up when you grab the deflection coil connector. :)
One of those DUH moments.

I still like the Wells Gardner 4600s better.....never been a big fan
of the g07's.
 
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