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over-driven GM tube.
wn4isx
One major problem with using GM tubes for radiation monitoring is they can overload and either go dead or produce an extremely low count, much below normal background. Scintalation counters can experience this too but only in intense, several thousand rad, radiation fields. That's why ion chambers have a place in the grand scheme of things.
The GM counters in the physics lab had what might be called a missing pulse detector. Say background is 30 counts per minute, the missing pulse detector produced an alarm if a count/pulse was missing for more then 20 seconds.
The effect is known by several names, it was called 'dead time' in our lab.
Modern tubes have better self quenching and are less likely to experience this.
It is a major? concern with pre ~1980ish surplus GM tubes.
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Re: Sort of improvised work bench
¿ªÔÆÌåÓýI had a PDP8I in a 19" 6ft high rack and when we moved in to a new house it occupied the spare bedroom. The mains is 240v in the uk. I would feel a "tingle" when I brushed my hand over the frame. Never had that in the previous home. On investigation
I found that the 3 pin wall socket had earth and neutral reversed. I checked every socket and foud one where live and neutral were reversed and 2 had the earth folded back also lots of loose screws.
Dave
Get
On 10 Dec 2024, at 12:19, Bertho <boman33@...> wrote:
Many decades ago, while working at Motorola, one of the engineering workbenches gave me a very slight tingle. |
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Re: Sort of improvised work bench
Many decades ago, while working at Motorola, one of the engineering workbenches gave me a very slight tingle.
I traced down the reason: The hot wire was interchanged with the ground wire! As a result, the workbench ground and all the test equipment were continuous at 120VAC. It had been that way for a long time. By luck there was no other grounded object within reach. Bertho |
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Re: Sort of improvised work bench
In that same vein, my electronics lab had several features I added after working on OH and CH downhole tools. Fashioned a Deadman Pedal that had to keep pressed to energize tool with 200-400vdc @ 2-5amps from a Sorensen supply.
Not quite related but shows spontaneous hazards... The tools would sometimes leak but not quite flood. Normally is just a PITA to clean up. Then I ran into my first Salt Water Saturation tool (used a 40curie Cesium source) that had H2S inside. Knocked me on the floor and was unconscious for several minutes. Regained consciousness in the back of an ambulance. Answer to that scenario was a klaxon wired to 30sec delay. Would turn it on when opening all tools coming back from sour wells. If reset wasn't hit after 30 seconds, sonalert would fire for 15 seconds, if that timer expired, very loud and irritating klaxon would sound off. All in shop trained what that sound meant, and would respond in SCBA (no 'U') gear. Needed that response twice. My battery Tek TDS2024 scope was a strange bird. No idea what option (attached to front) it had, but it had an input tolerance to 10kvpk with Tek probes, 1000vpk using typical X1/X10/X100 probes. Burned up so many Tek probes while probing HV that ended up buying by the dozen. Of course, this was when running on battery. Plugged in, I think was derated to 600vrms or similar. Spare batteries littered my lab. Incidentally, burned up the GPIB on day 2 due to static discharge, I think. Sign on exterior door " Danger! 10,000 ohms in use" kept a lot of looky-loos out. The braver visitors were usually turned back an over-driven GM tube. That just plain went *NUTS* several days after Fukushima! ~SD |
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Re: Sort of improvised work bench
On Mon, Dec 9, 2024 at 06:03 PM, wn4isx wrote:
I don't know if this is still taught, but in vacuum tube days, where lethal voltages were often exposed, they used to say to have a walking-cane nearby.? It must be wood.? And with the curved handle.? The cane is used to pull someone's arm or torso away from a "hot" circuit without becoming part of the circuit yourself.? Wood is a pretty good insulator when not wet.
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And from first-hand experience, the cane also comes in handy for daily exercises if someone is getting shoulder-related PT.? :-)? Or if you have trouble walking and actually need one to safely walk, as we get old.? :-(
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The last time I checked, a couple years ago, ordinary wooden walking-canes were still available at the local drug store chain.? Alas, checking just now at cvs.com, they no longer have the old traditional cane with the nicely rounded handle.? You need that so you can hook around someone's arm and pull.? Another drug store chain has them, about $15 online.? In-store prices are highly marked up by the likes of CVS so better bought online.
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Please don't take this safety stuff as if it doesn't matter.
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Andy
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Re: Sort of improvised work bench
¿ªÔÆÌåÓýAnd eliminating all the tracking nonsense: Please be aware that [often/usually] everything including and
following the '?' is information that web spyware use to track
your usage. Try cutting off that crap and protect your privacy a
little. (N.B. EVERYTHING utm* is spying on you. utm is the
"Universal Tracking Module" and it IS universal. It tracks your
web browsing wherever utm* element is appended to a link.) Donald. On 12/9/24 18:29, jong kung via
groups.io wrote:
[snip] |
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Re: Sort of improvised work bench
¿ªÔÆÌåÓýAndy,
It¡¯s this model (excstly) :
Originally they came with just one probe and nothing else. ?Now they include second probe as well as few other accessories. ? Those other accessories doesn¡¯t have insulated plastic cover over the BNC twist cover. ? That seems to be a weak point
(having metal exposed for operator¡¯s touch).
The BNC connector on the scope itself is recessed so that if 2 probes are connected, then it¡¯s actually harder to touch the exposed metal connector.
?= ?= ?= ?= ?= ?=?
What do you think about them as test devices for mains voltage ?
Jong?
On Dec 9, 2024, at 11:21 AM, Andy via groups.io <ai.egrps@...> wrote:
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Re: Sort of improvised work bench
wn4isx
A few comments on taking measurements on AC Mains. ? With the exception of rated battery operated DVMs or neon testers, don't unless you know exactly what you are doing, what you are measuring, why you are measuring it. ? AC Mains waveforms are boring, do you have a good reason to look at them? ? ? You want a safe work station with an obvious power off switch that does not take down the room lights. ? You want someone there who knows how to do CPR and a working telephone. ? I've played with direct mains powered devices since I was 8, I'm 73, and I've been knocked silly more times then I can count. ? I am extremely lucky, care to try your luck? ? Over 400 people are electrocuted in the US every year, better them 1 a day, 4000 are injured, more then 10 a day, feel lucky? ? Ground fault interrupters (residual current device in Great Britain) can help but also make you careless. Properly used isolation transformers can also help but again can make you careless. ? Ask yourself, is this project work dying over? |
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Re: Muddy audio in AF power amp
wn4isx
There weren't any harmonics but the audio sounded, and I hate this discriptor, muddy, smeared.
There might have been a very weak comb effect.?
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I fed band width limited white noise, sharp cut off at 20,000kHz, 9dB/octave, ran the amps at 10W and the mid range, ~1000 to ~4000Hz was "depressed."?
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In one of his good amps, the peaks of the white (random) noise form a nearly straight line, in the 'bad' amps, the midrange is down about 6dB.?
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I've seen noise spectra of many amps and never anything like this. I'd have expected the upper frequencies to be messed up.
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And the need for a ferrite bead in the collector lead as well as the base and a 10pF cap between base adn emitter....
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This was a dozzy!
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We modified enough transistors for 5 amps, they all worked fine and then we went out for a nice steak, his treat.
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Re: Muddy audio in AF power amp
¿ªÔÆÌåÓýExactly as I suspected. That means THERE IS harmonic distortion on a simple assembly. Thanks for confirming! Can I ask if you noted any of the harmonics at the audio part of the spectrum? ? Nuno T. From: [email protected] [mailto:[email protected]] On Behalf Of wn4isx via groups.io ? The new transistors are oscillating at about 1GHz, the frequency is frequency modulated by the incoming audio! ? The cure was a ferrite bead on the base and collector (now that's a first for me) and a 10pF SMD capacitor between base and emitter. I grabbed my Tiny SA on a wild hunch, found a spike and borrowed a Signal Hound USB spectrum analyzer to confirm the oscillation. ? The semiconductor industry constantly "improves" their products. Original 1N4004 switch slow enough to be a minimal EMI source, modern 1N4004 switch fast enough to be EMI sources from hell.? The silicon is purer, the junction is thinner and the turn off time is a lot faster. Someday really soon I hope to post a simple test device to see how much commutation noise a diode produces. ? ? ? ? ? -- Nuno T. |
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Re: Sort of improvised work bench
On Mon, Dec 9, 2024 at 12:58 PM, jong kung wrote:
That seems like a very VERY bad idea!? As in, a severe safety hazard.
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But I may not fully understand what you are asking.
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To me, DMM style implies having no metal on the instrument'that the user can touch.? That is probably OK.? Does your battery-operated scope have any touchable metal, anywhere?? If yes, then it's a hazard.? The scope's common could be 'hot'.
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Or are you suggesting letting the scope's common float (literally not connected to anything) and just connecting the two channel's inputs as if they were one differential input, letting the scope perform a subtraction?? That might work in theory, but I would not expect good results.? OTOH, safety-wise it is not good because there is capacitance from both inputs to scope common, and this makes the scope's metal float at 0.5 * the mains voltage.? NOT good.
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Andy
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Re: Muddy audio in AF power amp
On Mon, Dec 9, 2024 at 02:46 PM, wn4isx wrote:
I am trying to figure out if this is the start of a new conversation, or if it is meant to be a reply to another one.? Without any context, I assume it is the former.
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(It is quite challenging for me, trying to keep up with so many conversation in every interesting group.)
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With regards to RFI, oscillations, and changing,silicon, we do live in interesting times.? :-(
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Andy
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Muddy audio in AF power amp
wn4isx
The new transistors are oscillating at about 1GHz, the frequency is frequency modulated by the incoming audio!
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The cure was a ferrite bead on the base and collector (now that's a first for me) and a 10pF SMD capacitor between base and emitter.
I grabbed my Tiny SA on a wild hunch, found a spike and borrowed a Signal Hound USB spectrum analyzer to confirm the oscillation.
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The semiconductor industry constantly "improves" their products.
Original 1N4004 switch slow enough to be a minimal EMI source, modern 1N4004 switch fast enough to be EMI sources from hell.? The silicon is purer, the junction is thinner and the turn off time is a lot faster.
Someday really soon I hope to post a simple test device to see how much commutation noise a diode produces.
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Re: XLT 5000 PORTABLE RADIOS
wn4isx
There are no license free bands or frequencies in the 700~800 spectra.
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At the moment, December 9, 2024, the FCC has allocated 902-928MHz for license free part 15 operations.
There are many restrictions that might be both difficult to understand and comply with. However an industry group wants to steal some of the 900MHz part 15 frequencies.
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The FCC allows 2W operation on some FRS channels as part of the FRS license free system.
This would probably be more practical.
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Re: Sort of improvised work bench
¿ªÔÆÌåÓýHi group,
About an hear ago, I saw a portable (battery operated) 2 channel scope for approx $120-$200 (depending on max bandwidth) and bought one. ? While I never work on mains voltage, I figured it would be nice to have such unit just in case I ever get
the urge (to probe a 120v device). ?And sure enough I later decided I want to see the voltage wave form out of my battery backup UPS device.
But ¡. What is the industry opinion on using a portable ?/ floating (DMM style) scopes on mains voltage ?? ? Is it considered just as safe as using HV differential probes ??
Jong?
P.s. ? about my battery backup UPS - crappy waveform output. ?Luckily all my devices connected to it uses some form of switching power supply, so I¡¯m hoping that¡¯s good enough to undo the evils of ¡°modified¡± sine wave?
On Nov 26, 2024, at 8:10 PM, Kerim via groups.io <ahumanbeing2000@...> wrote:
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Re: Off topic, I will delete in a day or so.
wn4isx
I apologize, I thought the helium kills MEMS oscillators to be vaguely related to electronics but not related enough to stay "live" and intended to provide enough information for those interested in a relatively obscure failure mode of a device that is growing in popularity to be worthwhile posting.
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In the future I will try to only post stuff I consider valuable and relevant enough to remain live.
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My 'I won't delete' stuff wasn't about my own posts it was about posts with what I consider to be directly in violation of either US law or Groups IO rules.
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A "go here to steal this copyrighted material" falls under both categories. Even if the poster didn't fully appreciate the full legal ramifications of the post.
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I talked with a lawyer about a family legal mater, I own about 50 acres in Eastern Kentucky I want to donate to a trust for that side of my family. The land is worthless, no minerals, farmed to exhaustion by the wrong farming techniques, home to way too many copperheads, but the land has been in our family since a Revolutionary War land grant. I'm 73, have no children and wanted to protect the land after I'm gone. At 73 with total knee replacements in both knees, the chances of me ever hiking there again are remote.
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Our family lawyer is a junior partner in a local firm, she's also a cousin. She brought in a senior lawyer to discus possible conflict of interest because she owns the adjacent ~50 acres and wants to place her land in the same trust.
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The senior lawyer's specialty is intellectual property so I asked about the link to allow direct access to IEEE papers and was told that link was illegal and would be viewed in a copyright suit as furthering a criminal enterprise and the person posting it could well face criminal charges and a civil tort with significant financial losses. Group IO could have received a 'take down order' for this entire group.
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Of course I have no idea what the odds are the IEEE would ever find out, or if they are as draconian as some reports suggest, so I played it safe. an act I regret more then you can possibly understand or accept. If I had it to do over, I'd comment mentally to myself and carry on ignoring the post.
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My "I won't delete" applied to any post by anyone other then myself if I have reason to believe it violates the law or Groups IO rules. I will not delete anyone else's post if it includes detailed directions for obvious criminal acts such as "This is how to run a drug ring." This group is on it's own from me for that perspective.
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In the future I will try to refrain from posting topics that relate to electronics but are not clearly part of this groups mission, or might have a very small group interested in some arcane topic, as I understand it.
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In spite of my "I won't delete" if I realize I post something that violates Group IO policy, criminal law, or places me at risk of a civil tort, I will delete such posts without hesitation.
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However I doubt that will ever happen because I am extremely careful about the links I post.
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Sidebar as they said during a widely publicized trial....
When my department got our first Internet access, Bill Clinton had just given a speech and I was asked to find it. So I typed in Whitehouse.xxx, not knowing anything about domains I had no idea the proper domain would have been ".gov". Instead I brought up a webpage with naked women leaning out of every window in a photo of the Whitehouse. The entire office staff was there, 3 female producers, and 4 female administrative assistants. I froze in shock and disbelief for about 30 seconds before fumbling for the power switch and eventually turning the PC off. I was told later my freckles looked like dots of black ink against my white skin. We were visited by the 'campus porn patrol' later that day and given a stern warning about accessing such sites. The division head made it clear it was an innocent error, that none of us understood the xxx part of a webpage.
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So I accept being careful isn't always enough.
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It is possible, though extremely unlikely, I'll mess up the xxx and place a link to somewhere I don't mean to by accident, or a typo in the header of an address which could lead someplace unwanted.. Or a web page creator could let his lease expire and someone else take over who might post odd stuff. I'll admit if the later happens sometime after I make a post I'll probably never know about it unless someone flames me for the link. If I find out about such an incident, I will delete my post without hesitation.
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Again, please accept my apology and a promise to never ever post "OT will delete in x days" again along with a promise not to play Group IO's watchman and censor.
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If I post something I intend for it to remain online until Groups IO goes away.
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The only other exception to the "I won't delete' I can think of might be if I decided to leave this group, then I reserve the right under US copyright law to protect my material by deleting it. Since I'm not planning on leaving, that is unlikely and frankly I don't see that anything I've written and posted online in any group is worth that much effort.
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Without getting into the weeds or being accused of practicing law, under US Copyright law, the person who writes something other then a set of data owns what they wrote. There is no requirement to file a copyright form and copy of the material with the library of congress or to specifically claim copyright pm the work, the act of creating it makes it protected under US law.? ]paraphrased from the US Copyright office[
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J.D. Salinger, of Catcher in the Rye, stopped publication of letters he wrote based on the fact he owned the copyright of said letters.
[note the law then required filing forms to obtain copyright ownership.]
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Not that anyone would be the least bit interesting in collecting much less publishing the wit and wisdom of wn4isx.
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Re: oscilations in my amplifier ruins my PLL
On Thu, Dec 5, 2024 at 10:08 AM, john23 wrote:
Feedback. ?
Coupling.
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Andy
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Bertho
Gooey
to navigate to use esc to dismiss