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Re: Why you now Paypal
I've gotten it occasionally. I usually go there from what Firefox calls a private browsing window. Cookies aren't saved there and the first time going after restarting the browser is when I would get it, if I get it. Like I said, it's occasional.
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Vince - K8ZW. On 11/26/2020 12:09 PM, Frank DuVal via groups.io wrote:
Weird. I NEVER have a Captcha / Not A Robot screen or button when using --
K8ZW |
Re: Why you now Paypal
Weird. I NEVER have a Captcha / Not A Robot screen or button when using PayPal....
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I do not save my password. Have to enter it every time, my choice. Works for me. I do not understand the "how far along in the buying process you are" comment. All the screens on PayPal seem logical to me. And there are not many when sending money, either on their website only or through a vendor link to send funds. So far it works well for me! Both as buyer and sending money to friends. Even for Tek supplies, to keep it on subject.? Frank DuVal On 11/26/2020 1:01 AM, Jeff Dutky wrote:
I don't have particular issues, other than complaints about this particular process (not being offered the options that would have made this process easy), and about the quality of their buyer interface (every time I have tried to log into their web interface I have had to do the "I'm not a robot" dance, and every time the site has responded with "something went wrong on our end" throwing me back to the "I'm not a robot" screen, so that I get to do the dance again, and maybe a third time. That's shoddy UX on PayPal's part, and I haven't got any patience for that sort of thing. Also there's no indication of how far along in the buying process you are, so you just have to keep clicking Continue until suddenly the process is over. That's also shoddy UX). My only other complaints about PayPal are mere hearsay, but I've heard too many stories of sellers having their funds frozen over the years to think that maybe there isn't at least a little bit of fire behind that smoke. |
Tek 2xxx and 3xxx 56x series plugins available
Hello to all,
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I should have many 3A1/3A6 and other 56x series plugins in my stock.? The problem is they are on the other side of Ohio at my other house. Let me know what you want and I can look for them in a few weeks. Figure $20-$40 range plus shipping for most.? They will be complete (and most were tested/working years ago), but as-is now. I also have many letter and 1xx series plugins. You can email me direct at: jreese7010@... or phone: 740-947-7103 Regards, Jim Jim Reese Waverly, OH On Tuesday, November 24, 2020, 12:05:25 PM EST, Brenda via groups.io <brendda75@...> wrote:
Hello Dave, The 3A1 plugins that I have come across ends up not only the 6DJ8 tubes missing, there are 2 8233 tubes that end up missing as well.? There are 4 7586 nuvistor tubes in the front end, but seems like the tube pickers pass over these from my experience. I am in the market for a few 3A1 and 3A6 plugins myself...at a reasonable price, $400 is just way too much!! |
Re: A Couple Restorations
Bob,
Where are you located? there is a small handheld Tektronix scope in a surpus store near me and that I can probably get cheaply. As best as I can remember it is a 2xx model but I don't remember the complete model number. On Wed, Nov 25, 2020 at 10:09 PM greenboxmaven via groups.io <ka2ivy= [email protected]> wrote: My main pleasure with equipment is finding inoperative or basket cases |
Re: Resistor in series
Chuck Harris
Hi Tom,
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You must have done that calculation before the thread caught my attention. I've checked everything I wrote, and I don't see anywhere that I have said, "but they might still have made a mistake" as you appear to be attributing to me. When did I write that, or are you simply making up quotes for effect? Tektronix had excellent engineers. Way better than most, but in terms of reliability, they very often compromised the quality of their designs in production by using poorly specified parts, and cheese ball fixes for their mistakes. Their "tented" parts are legion, and some are very embarrassing to see as an engineer. (See 2465 A1 board for plenty of examples...) That said, it is a fool who changes the arrangement or parts selection, of an RF circuit he does not understand. -Chuck Harris Tom Lee wrote: Well, I've presented quantitative calculations explaining why capacitance matters in |
Re: (OT) Where to go for 70s IBM hardware? I'm looking for a terminal.
I have a pile of old IBM and Telex terminals from a local school system
when the state moved away from old IBM mainframes. They are stored in my garage, but I am unable to get to them without help. The IBM terminals are color, but I don't rember the model number. I believe they are RS232. Most of the Telex were dead, but I had swapped enough bords to get some of them to wake up. I am in North Central Florida. On Tue, Nov 24, 2020 at 2:03 PM cheater cheater <cheater00social@...> wrote: Thanks everyone. Not really bothered about the dependency on a control |
Re: Resistor in series
Carbon Composition resistors absorb moisture. Bake them for a while before
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tossing them out. Also, high value resistors require voltage across them to work at their marked value This used to be plainly marked on reels of CC resistors. I posted a scan once. I caught hell for 'making up that bullshit'. They also don't realize the first resistor series was 50% tolerance. yet they were working on pre-war radios. Once again I was told that I was 'making up that shit'. On Thu, Nov 26, 2020 at 12:18 AM Jeff Dutky <jeff.dutky@...> wrote:
Tom, |
Re: 7A26 no signal
I have just checked input resistances on a working-to-spec 7A26, the results are quite unexpected!. If I use an analogue meter and have the 7A26 powered off then in the 10mV position the DC 'resistance' from each BNC centre pin to its outer is about 350k measured in both polarities. For 20mV and higher the resistance is 1M. If I use a DMM then with either power on or power off the 'resistance' is 1M as it should be. Clearly Q150 needs to be powered in order to have its gate reverse biassed.
Even if Q150 is faulty, its output, together with the output from the 2X balance pot R160 form the two inputs to the differential amplifier U1350, so if U1350 onwards is all OK, the trace should move. I have just noticed that there is another DC balance pot (R1353) between U1350 and U1450 so that can also be used to narrow down where the fault is. Since the two beams do move in response to the vertical position front panel control it looks like U1550 in each channel is OK so you can swap the good IC from one channel to the suspect position in the other channel and see what changes. Regards, Roger |
Re: Why you MUST USE the PayPal "FRIENDS and FAMILY" option for Peter's book
On Thu, Nov 26, 2020 at 03:01 PM, Jeff Dutky wrote:
....I thought about this a bit, with the huge volume of paypal transactions every day across the world, the actual number of horror stories would have to be a fraction of a fraction of a percent. |
Re: Delay Time Position Vernier
I don't recall seeing it in any Service Manual, but our good friend H?kan has produced a document on the topic:
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Colin. -----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Jeff Dutky Sent: 26 November 2020 00:24 To: [email protected] Subject: Re: [TekScopes] Delay Time Position Vernier Colin Herbert wrote: Is this covered in the service manual? I would be interested in knowing how this needs to be set, as I am planning to move the guts of one 475 into the frame of another, and that would obviously involve disassembling and reassembling the delay vernier. -- Jeff Dutky |
Re: Tektronix 492A input attenuator repair ????
Once I had the same issue with the 492 attenuator. Taking it carefully apart, one of the wafers was burned. I was able to manufacture a wafer myself, using very thin teflon laminate and 0402 SMD resistors. The result was acceptable up to about 8 GHz.
Cheers Ulf Kylenfall SM6GXV |
Re: Resistor in series
OK, yuzz made me look. I found the schematic for the 475A, and my quick assessment is that there's nothing special about low capacitance or inductance or precise value of the R1356/R1544 combo. I also looked at the regular 475 schematic, which appears about the same. Without seeing the actual physical layout, I'd guess that the circuitry is quite crammed in there for space reasons, and two 1/2W resistors "fit" better than a single 1W piece - enough so that it was worth continuing the tradition over modifying the board layout.
Q1344 and Q1352 form a shunt-feedback linear amplifier, and the rest of the circuitry handles all the various conditions the Z-axis must take, which are plentiful. The collector of Q1352 is a low impedance node by virtue of the amplifier power gain, with DC feedback from R1369, while C1352 provides AC feedback and compensation. The output has to drive the DC restorer, a significant capacitive and nonlinear load. R1368 isolates the DC restorer load, and C1352 stabilizes the amplifier - it would likely oscillate otherwise. The presence of all the diode clamps and blocks in the amplifier stages indicate a number of operational conditions are needed, depending on what's going on in the horizontal system.Q1352 provides strong pull in the down direction, while Q1358 and Q1354 form a cascode amp for the up direction, but only during transient conditions - at DC, it's a constant current source. It looks like the two Rs in question supply collector load current for Q1352 whenever Q1358 is in cutoff, to keep the loop closed and ready for fast response to the next event, or from overdrive recovery. Z-axis amplifiers don't need high fidelity, but do need fast response in one direction at least, to properly unblank at the beginning of the trace. The tail end (blank) can be slower since the trace is usually off screen by then. So anyway, I wouldn't worry too much about these resistors. Yes, there must be a reason they went this way, but whatever it is, I don't think there's anything critical about these parts. The maximum DC in them should be about 7 mA, so about 700 mW, when the output is held near zero. Two 1/2W resistors standing upright should handle it OK - better than a single 1W part laying on the board. Happy Thanksgiving all. Enjoy. Ed |
Re: 7A26 no signal
Colin and Juoko,
If the 7A26 is arranged anything like the 475 then cleaning the AC/GND/DC coupling switches is almost exactly the same as cleaning the rest of the attenuator switches: soak a narrow strip of 100% cotton bond paper in IPA, slide it between the open switch leaves and the contact plate on the PCB, close the switch trapping the strip of paper, gently pull the paper out, and repeat several times for each contact point. I found the process more difficult for the attenuator switches on the 475 because you have to remove each attenuator block to get access to the switch contacts, and because there are contacts on both sides of the PCB, the ones on the bottom side being significantly more difficult to access. That said, with patience and diligence I was able to clean all the switch contacts, so I think you shouldn't have any trouble. -- Jeff Dutky |
Re: (OT) Where to go for 70s IBM hardware? I'm looking for a terminal.
Wish I had kept my Commodore PET/CBM systems...
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-Dave On Wednesday, November 25, 2020, 05:59:43 PM PST, - <rrrr6789@...> wrote:
Actually $1200 is completely reasonable IMO. I sold mine for almost that much 15 years ago and i've seen at least one that sold for almost double that. Like the prices or not but the really unique and/or first of it's kind vintage computers are bringing serious money. Even good, clean and complete Commodore 64s and the Radio Shack computers are bringing hundreds of dollars and they were sold by the millions. On Wed, Nov 25, 2020 at 2:00 PM cheater cheater <cheater00social@...> wrote: Those prices are not reasonable, and the sellers do not accept offers, |
Re: Why you MUST USE the PayPal "FRIENDS and FAMILY" option for Peter's book
John Goller wrote:
I don't have particular issues, other than complaints about this particular process (not being offered the options that would have made this process easy), and about the quality of their buyer interface (every time I have tried to log into their web interface I have had to do the "I'm not a robot" dance, and every time the site has responded with "something went wrong on our end" throwing me back to the "I'm not a robot" screen, so that I get to do the dance again, and maybe a third time. That's shoddy UX on PayPal's part, and I haven't got any patience for that sort of thing. Also there's no indication of how far along in the buying process you are, so you just have to keep clicking Continue until suddenly the process is over. That's also shoddy UX). My only other complaints about PayPal are mere hearsay, but I've heard too many stories of sellers having their funds frozen over the years to think that maybe there isn't at least a little bit of fire behind that smoke. That said, I understand why people want to use PayPal: they fill a niche that, even today, has very few players. If you want to accept payment over the web you just don't have many choices, and the established choices (credit card merchant accounts) are not well suited to small players. When PayPal got started they were basically the only game in town for people who couldn't afford to set up a merchant account, and that benefit can not be overestimated. Still, I'm a grumpy sort, and this is one of the things I'm grumpy about. -- Jeff Dutky |
Re: Resistor in series
Hi Jeff,
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I've only taken a quick look at the circuit, but it doesn't look overly fussy about the exact resistance value, so the carbon comps you bought are likely to be fine if they are still within tolerance. So don't rule them out just yet. The noise of a carbon comp is indeed truly wondrous (and it is proportional to dc current; film resistors do not exhibit this effect to any significant degree), but in this particular circuit, the noise isn't of consequence. The signal amplitudes there are so much larger than the noise that you'll never see any effect. So, if you find that the AB resistors you just purchased are within tolerance, I think there's no harm at all in using them. I have to admit to sharing the same nostalgia that you have for these retro resistors. But beyond that, there is also one sound engineering reason to keep some around: Better surge tolerance, owing to the current being distributed over a larger cross section than is the case with film resistors. I'll occasionally specify CCs for circuits that may experience transient overloads, such as some HV circuits which may arc occasionally. Metal film resistors don't tolerate transient overloads as well. -- Cheers, Tom -- Prof. Thomas H. Lee Allen Ctr., Rm. 205 350 Jane Stanford Way Stanford University Stanford, CA 94305-4070 On 11/25/2020 21:18, Jeff Dutky wrote:
Tom, |
Re: Resistor in series
Tom,
Yes, I had anticipated that these NOS components might not have retained their specified values. I've been going through my father's effects while working on his scopes and finding all sorts of now-50-year-old components, some of which were expensive when purchased new, and thinking that some fair fraction of them are probably now terribly out of spec, if not completely destroyed (there are a number of big metal can capacitors that I know were stored for at least 20 years in a hot attic, and I don't have much hope that they are still in good condition). I purchased a dozen resistors in the hope that I could find two that were within spec. Back in college I worked in receiving QC for a NASA contractor that built flight-rated systems. We would first receive a lot of 10 or 20 components of some description, which we would label and ship over to Goddard. They would eventually ship us back 2 or 3 components with paint marks and certification sheets, and we were required to use only those marked components in the parts we built for them. The other components we had shipped to them had been tested to destruction, and only the surviving 10% had been returned to us as flight qualified components. Careful selection of parts is something I have thought about ever since. But what you're saying is that while my intuition was correct, the actual math makes a fool of me. I should really just use the metal film resistors when they arrive because they are lower noise and the inductance is a non-issue. I can always gaze lovingly at the old Allen Bradleys. I'm quite sad that nobody seems to make resistors that have those nice sharp edges anymore (or, at least, I haven't found them for sale). -- Jeff Dutky |
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