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Re: lethality of HV
Craig Sawyers
Most oldOh dear - maybe I now class as an old timer ;-) I learnt respect for hight voltage in the 1970's when I built an experimental pulsed carbon dioxide laser. This thing had an array of high voltage ceramics totalling 20nF charged up to 20kV (4 Joules). In the dark you could see any sharp corner glowing blue with corona discharge. Boxed the thing up in a copper foil lined perspex box with a hefty strap to ground to make sure that any unpleasant event went somewhere safe. And yes - while measuring anything on this lethal beast (using a P6015) one hand was very firmly in the pocket. I nearly gave a colleague a heart attack with one episode - I managed to get the probe tip half way between the top and bottom plate that sandwiched the capacitors - and it arced across top plate-probe-bottom plate with a huge BANG. Gave me such a fright that I yelped, and my colleague ran in with a white face expecting to find me on the floor. It really stuffed the screw-on tip of the probe too.... Although that was bad enough, this thing spat 0.5 Joule pulses of light out (in the infrared) with a pulse length of about 100ns - a peak power of 5MW. Of course over the years I have had the odd lapse of concentration - like the belt from the 7704A HT supply - but fortunately I've got away with it so far. Might have to revisit the care I take now the years are passing. Craig |
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Re: lethality of HV
In the Tektronix book "Biophysical Measurements" book, it states that it
only takes 10mA of current to stop the human heart if a circuit path through it is created (like hand to hand or hand to foot). Most old timers put one hand in their pocket so that there is no path. You will still get an alarming little shock but it won't be lethal. The threshold of pain is about 1 mA. Conversely most pacemakers only generate 10 microamps to pace the heart. Your friend is wise to be afraid. I have worked in more than one shop where a person was electrocuted due to carelessness. One must respect high voltage and electricity 24/7. I also belong to a Hammond organ technical group and it never ceases to amaze me the risks some people take. I am constantly telling people to hire a professional technician if they are not absolutely certain of what they are doing. Vintage tube equipment has many different lethal voltages. You will notice that in almost every manual, even for the TM series, warnings about lethal voltages inside. I know that most of you are seasoned technicians - this is more directed to newbies and persons more used to CMOS and TTL voltages in digital equipment. |
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Re: lethality of HV
More about static electricity - it takes 5kV to even have a sensation from
it, due to skin resistance, etc. That is why static damage is so easy. Some components like JFETS can be damaged at potentials under 100V. I use an antistatic workstation and wriststrap all the time. If you live in a dry environment there is even more risk of static damage (or have nylon carpets in your shop area). I even have a static locator to identify and remove static generating materials from my "protected area". Some of the worst offenders are packing materials. Very few people use antistatic packing materials. Bubble wrap and styrofoam peanuts (& coffee cups) are the worst. Even your clothing can generate dangerous levels of ESD. Stick with natural fibers. Static damage is rarely immediate - it creates a "walking wounded" component that can fail a year or more out. The carbon generated from the ESD strike can cause a transistor junction to "grow" over time, temperature and other conditions in IC's. Antistatic straps have a 10Mohm resistor built in for safety reasons. In my car I use an insulated key as a lightning rod which lessens the shock immensely. I used to set up and train employees in medical manufacturing companies about ESD control. |
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Re: lethality of HV
When I was in technical school I spent many evenings and weekends repairing
50s TV sets and never had a problem keeping away from the HV. Then I spent 20 years working on solid state electronics, mostly audio. I got quite used to using my fingers as signal tracers. Finally I decided to work on one of the old TV sets. I was amazed at how hard it was to keep my fingers out of the set. I kept wanting to touch a tube socket to see if that would effect the signal. Perhaps the more experience one has with modern electronics, the more dangerous it might be for them to work on an old 500 series scope! Mike Csontos |
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Teknet manuals
Hi guys:
If you read the info on the site there is a disclaimer that says that there may be omissions and that they are asking for information from the users to point out these problems. I believe they say that they will make sure you get a corrected copy. For a free service I don't know how much further they should go. They do have original copies for sale. Another point is that I have been to their facility and found that they are a very well qualified team of technical people. I was impressed with the people, the technical lab and the management. They are in the process of moving from the Chicago area to Atlanta. From my experience in technical management, I know that you don't relocate marginal people. They have a good inventory of equipment for sale. I may have missed the point but I was not aware that the primary business was rental. George Atlanta Sign up for Internet Service under $10 dollars a month, at |
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Re: lethality of HV
Craig Sawyers
A friend of mine is afraid to work on a three gun projector,It all depends on the current. For an anode accerating system, there is very little (or no) current, so the power supply only has small capacitors in the voltage multiplier. There is maybe 10-20 milliJoules stored. Remember that the human body has a capacitance of 160pF typically, and you get a static charge walking across a rug or stroking a cat of about 10kV in dry conditions. You can certainly *feel* that - it causes me to yelp every time I get out my car in dry weather - closing the door is a real adventure. As to the lethality, I don't know the formal details, but I gave myself a fright with my 7704A once. In a moment of brain fade I unplugged the HT from the CRT (with the scope off), and made the mistake of touching the exposed pin on the connector where it exits from the supply. Youch! Of course the capacitors hold the charge (duur), so you get a nice 21kV belt. It is enough to make you not want to repeat the exercise, but I'm still here to tell the tale. The anode supply in older scopes is far more dangerous, because you have maybe 500V after the rectifiers across around 150uF of smoothing capacitor. That is 9 Joules, and more than enough to send you off to the pearly gates if you grab it with a vengeance. Once the skin is punched through, the body's resistance is only around 100 ohms - so you get 5A flowing from the 500V for 15ms (RC time constant). A rather scary site at t.html says that 5A (but for 1 second) causes "Ventricular fibrillation (the rhythmic pumping action of the heart ceases.) Muscular contraction and nerve damage occur. Death is most likely." I guess that the energy comes into this - so 5A for 15ms is the same as 75mA for 1 second. They say about 75ms "Extreme pain, respiratory arrest, severe muscular contractions. Individual cannot let go. Death is possible." So watch that old tubed gear! Craig |
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Re: 7704a
Craig Sawyers
Would someone post a quick opinion on a 7704A with (3) 7A26 DualNice system. My every day 'scope is a 7704A with a selection of plug-ins depending on what I'm doing. I use the 7B80/85 combo though, becuase it allows you to do delta time measurements, whereas the 7B70/71 doesn't. Craig |
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lethality of HV
Robert Morein
A friend of mine is afraid to work on a three gun projector, which coincidentally has the same anode voltage as the 7704, 7904, etc, 24 KV.
It is my understanding that this voltage is not lethal, primarily because the CRT is too small to store a lethal charge. Elsewhere, I have read that the lethal threshold, at least as far as TV tubes are concerned, is around 32 inches. Comments? Any reassuring words for my friend? |
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Re: 7704a
Robert Morein
Great scope.
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The timbases are older than the scope, but compatible. The optimal timbaes are 7B80 (horizontal slot 2, main) 7B85 (horizontal slot 1, delaying) The 7A18 are inferior to the 7A26, but you can use them for high voltage experiments ;) The 7B53A does not reach the maximum sweep speed of the scope. It is compatible, but intended for the 7603 series. The 7D15 is a gem, and fits in horizontal slot 1. ----- Original Message -----
From: Brian Goldsmith To: tekScopes@... ; Dennis L. Wade Sent: Saturday, March 06, 2004 12:39 AM Subject: Re: [TekScopes] 7704a ----- Original Message ----- From: "Dennis L. Wade Would someone post a quick opinion on a 7704A with (3) 7A26 Dual Trace Amp, (2) 7A18 Dual Trace Amp, and one each of 7B70 Time Base, 7B71 Delay Time Base, 7D15 255 MHz Universal Counter Timer and 7B53A Dual Time Base. *** Nice!!!!! Quick enough? :-) Brian Goldsmith. ------------------------------------------------------------------------------ Yahoo! Groups Links a.. To visit your group on the web, go to: b.. To unsubscribe from this group, send an email to: TekScopes-unsubscribe@... c.. Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service. |
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Re: 7704a
Brian Goldsmith
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----- Original Message -----
From: "Dennis L. Wade Would someone post a quick opinion on a 7704A with (3) 7A26 Dual Trace Amp, (2) 7A18 Dual Trace Amp, and one each of 7B70 Time Base, 7B71 Delay Time Base, 7D15 255 MHz Universal Counter Timer and 7B53A Dual Time Base. *** Nice!!!!! Quick enough? :-) Brian Goldsmith. |
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7704a
Dennis L. Wade
Would someone post a quick opinion on a 7704A with (3) 7A26 Dual
Trace Amp, (2) 7A18 Dual Trace Amp, and one each of 7B70 Time Base, 7B71 Delay Time Base, 7D15 255 MHz Universal Counter Timer and 7B53A Dual Time Base. Thank you...Dennisopinion----------------- "If you can remain calm, you just don't have all the facts" Dennis Wade KG6ZI Carmichael, CA |
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Re: Bias batteries in 7S14
I was eager to check out the teknetelectronics site Jeans wrote about:My understanding is that 'membership' is free. They never collected any fees from me, did not even try to. Keep in mind that company is in rental business and purpose of this site is to substitute missing operating manuals. No rental customer repairs or calibrates equipment and I was surprised to find any service manuals. I guess, those are the ones that leaked through the system. The manuals I downloaded were incomplete and disorganized as if whoeverI would say, there is no 'as if', guy who ran paper through the scanner did not care what came out as long as it was any kind of image. Since I am into guessing business, I would say that scanning was done by a service company and when customer asked why pages are not aligned they told him that can be done, too, but price is triple. As for incomplete manuals, I would guess that parts were omitted to save the cost. As I already said, those manuals are intended for rental customers to use as operating instructions. Few manuals that have schematics, surprisingly one for 7S14 does, are possibly early scans, before accountants got billing for scans or ones that leaked through the system. I would be very hard pressed to argue differently, even when talking about good scans, like ones available on e bay, but for something that I would just glance at, like things that I do not own but am curious about circuit, scans would have to do. Any kind of a small paper manual (e.g. for plug-in) is upward from $10, frequently $20 and that makes it an expensive proposition. As for good way to scan fold out sheets, there is a claim by one e bay vendor that he has a scan of the whole page and if printed at the place that can handle B size paper, fold out sheets are usable. Have not seen any of those schematics, just saw vendor's claim. Regards Miroslav Pokorni |
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Re: Bias batteries in 7S14
Dennis Tillman
Hi Everybody,
I was eager to check out the teknetelectronics site Jeans wrote about: in hopes I could find a few of the really rare manuals I still haven't been able to locate for my collection. But the site is a bit of a disappointment. The quantity is there but the quality is lacking. When you sign up for the free 30 day trial you can download 5 manuals. But unfortunately you get what you pay for. They are free. But if the three Tek manuals I chose to download are any indication of the overall quality of the site I would not be willing to pay for a subscription. The manuals I downloaded were incomplete and disorganized as if whoever scanned them was not paying attention to what they were doing. Personally I prefer paper. Its much easier to grasp the big picture with a paper manual and as far as I know no one has yet to come up with a good way to scan the foldout pages. For those people who prefer their manuals in PDF format I would suggest buying from one of the people selling them like that on eBay. The eBay sellers have more of an interest in maintaining their reputation for doing a quality scanning job. Dennis |
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Re: 647 cal fixture on ebay
Snort!
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Seriously, it's not ham shorthand at all, it's chatroom shorthand, stands for If I Recall Correctly. Other related ones: AFAIK As Far As I Know YMMV Your Mileage May Vary These serve to delineate precisely how much you do *not* know about what you're talking about :) Regards, Dave Wise -----Original Message----- |
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Re: ligthing gel
Thank you, Craig. That was very smart of me: said 'lighting gel' and then
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went on about photographic filters. Regards Miroslav Pokorni ----- Original Message -----
From: "Craig Sawyers" <c.sawyers@...> To: "TekScopes" <TekScopes@...> Sent: Friday, March 05, 2004 1:09 AM Subject: [TekScopes] ligthing gel film,You did mention that lighting gel before, but I still do not besomething to be used to make custom photographic filters. The film must collapsing?very thin, to avoid optical distortions due wavy surface caused inPlease, explain the construction.Lighting gel is the stuff that is used in front of stage lighting in front of Tek scopes for sure - but it would certainly be better than |
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Re: Bias batteries in 7S14
Michael Dunn
At 12:22 AM +1100 2004/3/6, jeans wrote:
You can download the instruction Manual from TekNet at Thanks! I've added their URL to our Links page. I'd advise any members who haven't checked out that page to do so sometime. Lots of good stuff... Michael |
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Re: 7S/7T Sampling System
Ashton Brown
Craig, thanks!
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+11 Informative.. Your post encapsulates about a dozen questions I've had re refurb of the pure unobtainium stuff. Printed! It's Very nice to know that, with some precise fiddling - many of these can be resurrected. (And thanks to Stan, repeatedly - for supplying the unobtainium Information!) GaAs back with a vengeance, eh? 150 Ghz might get us 5000 Channels - with nothing watchable.. Two ears and a tail - {static-free, of course} Ashton Craig Sawyers wrote: I have read postings about using some fast SchotkyI did this with a defunct S3a 1GHz sampling probe. The brige was toast |
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Re: 475A filter, protective cap availability?
Robert Morein
Lighting gels are not very thin, because they are mounted in front of
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lights, not lenses. The dye is "cast" into the material. ----- Original Message -----
From: "Miroslav Pokorni" <mpokorni2000@...> To: <TekScopes@...>; "Mark Anton" <heightstv@...> Sent: Friday, March 05, 2004 3:07 AM Subject: Re: [TekScopes] 475A filter, protective cap availability? Hello Mark,what is that material and why musical instrument repair shops would have it.mounting. In that case, how you would make a 4 x 6" screen without film collapsing?repair getshop should possibly have some. The only to be careful of is not too fartherone that is too opaque. Then you would have to turn up intensity scopesthan needed to view the trace. I have used gel material on several CRTnow and works well. It isnt just for looks either...the reason it isthereis to provide a higher contrast trace. vs seeing a white background. filter with a nice sharp new one. Ar they commonly available? |
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