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Resistor in series
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Manahem,
As it happens I have chosen to leave the existing carbon comp resistors in place, which replacing the failed transistors and diodes. After replacing the failed transistors and diodes the scope seems to be working perfectly (at least with regard to the beam intensity and blanking). I have replacement NOS carbon comp resistors on order, but I'm not going to use them unless the Z-axis amplifier starts acting up again. I will look into getting new production parts as you suggested, and look for ceramics, as I would like to have something in my stock other than just metal and carbon film resistors. -- Jeff Dutky |
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That's good information Menahem. Thanks for posting it.
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I'll just add that I have a large number of 40-ish year old Allen Bradley carbon comp resisters, many of them still in the factory sealed packages. I have probed through the packaging and measured many of them and they're ALL well out of spec! So don't trust old carbon camp resisters even if they've never been used. Seeing how far out of spec that many of these resisters are, it amazes me that any of this old equipment that uses them still works! On Mon, Nov 30, 2020 at 3:50 AM M Yachad <yachadm@...> wrote:
Jeff |
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Probably the old equipment was designed to be insensitive to exact values of carbon comp resistors.? Kudos to the designers for robust designs.Jim Ford?Sent from my Verizon, Samsung Galaxy smartphone
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-------- Original message --------From: - <rrrr6789@...> Date: 11/30/20 11:47 AM (GMT-08:00) To: [email protected] Subject: Re: [TekScopes] Resistor in series ? That's good information Menahem. Thanks for posting it.?? I'll just add that I have a large number of 40-ish year old AllenBradley carbon comp resisters, many of them still in the factory sealedpackages. I have probed through the packaging and measured many of them andthey're ALL well out of spec!? So don't trust old carbon camp resisterseven if they've never been used.? Seeing how far out of spec that many ofthese resisters are, it amazes me that any of this old equipment that usesthem still works!On Mon, Nov 30, 2020 at 3:50 AM M Yachad <yachadm@...> wrote:> Jeff> Choosing a substitute resistor type, as others mentioned here, is not a> simple matter.> You really need to know what its function is in the circuit.>> Carbon Comp resistors are the only absolutely suitable choice, if the> circuit has current surges.> Film resistors of all types simply cannot handle the range of current> surges.>> If you really cannot find a Carbon Comp (and the circuit requires it),> then a Ceramic MAY be a good substitute, and if you are still really stuck,> then the next possible substitute is a Metal Oxide type. BUT, Metal Oxide> starts to introduce inductance into the circuit.>> Carbon Comps also have no inductance (inductance kills - as in obliterates> - performance in RF circuits).>> Now, Ceramics come in two types - Inductive, and non-Inductive. Again, For> an RF circuit, ONLY a NON-Inductive is suitable.>> Notice that I haven't even mentioned film resistors.> On these vintage machines, you really want to investigate using Carbon> Comp or Ceramics first, to solve the problems, without introducing new> problems!>> Your choice was correct to use Carbon Comps, but I would recommend buying> new production pieces from Mouser or Digikey. Highly unlikely that you'll> find significant deviations due to moisture in cracks, or whatever..>> Menahem Yachad> CondorAudio>>> >>>
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On Mon, Nov 30, 2020 at 11:48 AM, - wrote:
For A.B. "hot-moulded carbon composition resistors" (for Panasonic ones too) the effect of "moisture" ingress (a.k.a. gaseous water molecules = water vapour = moisture) is to always increase resistance. According to several citations, this ingress is always reversible, with the appropriate time, temperature, and humidity conditions. (Older resistor manufacturing technologies might have used materials to comprise the resistance element which might have undergone strongly irreversible chemical reaction(s) with the ingressed "moisture...this perhaps causing a permanent change to the the resistor's nominal resistance.) How one measures the resistance (for hot-moulded carbon comps) and compares it to their nominal value, depends on how the manufactures standardized their measurements... or that done in accord with the institutional standardizations the manufacturers adhered to. (Very generally, high values of resistance need to be measured at high voltages [without causing significant temperature increases]... and low resistance values can be measured at lower voltages. You have to know how the manufactures did the measurements. |
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Bob Albert
I don't think the procedure for proper measurement of resistance would have an appreciable effect on a resistor that is grossly out of specification.? Maybe for nitpicking whether it's in spec or not, but not for gross errors.
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Bob On Monday, November 30, 2020, 04:39:57 PM PST, Roy Thistle <roy.thistle@...> wrote:
On Mon, Nov 30, 2020 at 11:48 AM, - wrote: For A.B. "hot-moulded carbon composition resistors" (for Panasonic ones too) the effect of "moisture" ingress (a.k.a. gaseous water molecules = water vapour = moisture) is to always increase resistance. According to several citations, this ingress is always reversible, with the appropriate time, temperature, and humidity conditions. (Older resistor manufacturing technologies might have used materials to comprise the resistance element which might have undergone strongly irreversible chemical reaction(s) with the ingressed "moisture...this perhaps causing a permanent change to the the resistor's nominal resistance.) How one measures the resistance (for hot-moulded carbon comps) and compares it to their nominal value, depends on how the manufactures standardized their measurements... or that done in accord with the institutional standardizations the manufacturers adhered to. (Very generally, high values of resistance need to be measured at high voltages [without causing significant temperature increases]... and low resistance values can be measured at lower voltages. You have to know how the manufactures did the measurements. |
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My own experience in the resistor business was long ago and did not include "mud" resistors. However, the only reason I can see that voltage might make a difference is if the resistor had a very high voltage coefficient of resistance. Composition resistors do have some while metal and carbon film resistors have virtually none. Nonetheless, the voltage at the terminals of a bridge or even a VOM should not make a significant difference.
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?? AFAIK the drift in composition resistors had to do with heat. The resistance element is made of many small particles of conductive material (carbon) embeded in an insulating material. As resistors age there tend to be fewer contact points between the small conductive particles so the resistance goes up. Excessive heat also causes this effect, again with an increase in resistance. I have observed resistors where the resistance has gone down. I don't know the mechanism but these were all very low value to begin with. ?? I have not tried baking old composition resistors but if the original drift was caused by heat I don't see how baking would restore the original value. Perhaps if its due to moisture penetrating into the jackets it would. ??? FWIW Allen Bradly made the Ohmite Brown Devil resistors, all came from the same place. Ohmite mentions this in their early advertising. I don't know why two brand names were used. In general, these seem to have been the best of the carbon composition resistors although I have no data on IRC resistors. I do remember being told when I was studying engineering to avoid IRC. ?? The reason composition resistors were never available in tolerance less than 5% is that the heat of soldering could change the value more. ?? These days, with cheap carbon film and metal film resistors easily available there is no reason IMO to use composition resistors. While at one time they were thought to have lower reactance at RF they provably do not. Supposedly composition resistors have some advantage for pulse use but I may be remembering that wrong. On 11/30/2020 5:22 PM, Bob Albert via groups.io wrote:
I don't think the procedure for proper measurement of resistance would have an appreciable effect on a resistor that is grossly out of specification.? Maybe for nitpicking whether it's in spec or not, but not for gross errors. --
Richard Knoppow dickburk@... WB6KBL |
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On a few occasions I've had to trim carbon comp resistors by carefully
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filing partially through the body with a fine file or a fine saw. In one case I know that the packaging machine that I installed one of the trimmed resistors in was still running fine over two years later. On Tue, Dec 1, 2020 at 8:12 AM SCMenasian <scm@...> wrote:
In my earlier days (pre 1970), I used to "trim" carbon composition |
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In my little post I mentioned working in a resistor factory during part of mis-spent youth. We made film resistors exclusively so I don't know a lot about making composition resistors. However, I wonder about improving stability by baking. One would think if this worked it would have been routine. Maybe it was to some degree. We cycled the film resistors through hot and cold. That was partially to stabilize them and partly required tests for the mil spec they had to meet. The temp cycling was done both before and after spiraling. I am pretty sure composition resistors like the Ohmite/AB ones were hot molded. I have no idea what IRC did except they look quite different and advertise a different internal construction. I almost never see IRC resistors in old equipment. Not cost because the catalog prices or Ohmite and IRC were the same. There were some very unstable resistors around, one finds them in old Hallicrafters radios. I have no idea who made these, they are not either Ohmite or IRC and often have a seam running lengthwise. Same in Drake equipment, composition resistors with seams are very unstable. Maybe they leak moisture more.
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?? When I dealt with resistors film types were significantly more expensive than composition. They were used where precision and stability were necessary. In those days 10% was the common tolerance and 5% were available at extra cost. For greater than that, say 1%, one had to go to film resistors or precision wire wounds. These days 5% seems to be standard and 1% are cheap. On 12/1/2020 5:12 AM, SCMenasian wrote:
In my earlier days (pre 1970), I used to "trim" carbon composition resistors by carefully overheating them with a soldering iron to raise their values slightly. This may have also improved their stability by getting the early ageing out of the way (although I never verified this). --
Richard Knoppow dickburk@... WB6KBL |
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Hi Jeff,
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Thank you for that link to Gale Morris' comments at the vintageTEK museum. I had no idea IBM was already building their own scope for their Service Engineers. When I was half way through my Junior Year in college I bought my first Tek scope and it was a 453. It cost me $2,000. This turned out to be the greatest investment I ever made in myself. I came home from college every day and I would experiment with everything I was learning in school. The results were right there on the screen of the CRT for better or worse. After a dozen more tries I would sometimes be successful making my circuit work. Along the way I managed to make that scope do a huge number of things most engineers had no idea it could do. To this day I love figuring out how to make measurements with Tek's scopes that are impossible with scopes designed by other companies. I sold my 453 ten years after I bought it for the exact price I paid for it. That $2,000 paid for my 7704A mainframe. My close friend bought the plugins (a 7A26, 7B80, and 7B85) so we were all set except for the empty fourth slot which annoyed me. So I bought a 7A17 to fill that hole. For the next several years we shared that 200MHz 7704A scope. Dennis Tillman W7pF -----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Jeff Dutky Sent: Friday, November 27, 2020 3:28 PM To: [email protected] Subject: Re: [TekScopes] Resistor in series Here's an oral history video discussing the history of industrial design at Tek: The speaker is the former head of industrial design at Tek (Gale Morris) and he mentions (possibly hyperbolically) that the 453 sold 70,000 units in a single shot to IBM, so the pennies can really add up. -- Jeff Dutky -- Dennis Tillman W7pF TekScopes Moderator |
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Jeff,
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Wow! The Gale Morris interview is great. I especially liked the part where the IBM guys take the scope away and tells the two sales reps, ¡°If we can¡¯t figure out how to use it by sitting and looking at it we don¡¯t want it.¡± Good industrial design was always integral to Tektronix products. I¡¯m reminded of one of my favorite Jim Williams quotes about Tek scopes, ¡°The engineering concepts and production were a bumpless combination of interdisciplinary technology, inspired design, attention to detail, aesthetics, and usability. The thing just radiated intellectual honesty.¡± Dennis, What a great story about your 453. A tektronix 453, with the IBM logo, sat on my desk at work, used mostly for checking audio files, until I retired last year. George On Dec 1, 2020, at 5:02 PM, Dennis Tillman W7pF <dennis@...> wrote: |
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From what I can find about carbon composition resistors, the resistive element is a composite of finely ground carbon granules and a binder.
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The amount of carbon granules in the binder determines the resistance. The resistive element is enclosed in a casing material with the leads protruding. With age, moisture permeates the seals around the leads or through a crack in the casing. When the moisture permeates the binder, the binder swells and places the carbon granules further apart, increasing the resistance. If the binder swells enough, it will crack the case. Heating the resistor to drive off the moisture and the pressure from the inside of the case will compress the binder to close to its original size. However, the dead is done. The case now probably has a minute crack in it due to the pressure. Now there is another place for moisture to migrate back into the binder. I consider any out of tolerance, high, carbon composition resistors to be bad and will replace them now that I have an understanding of the failure mode. The resistor, upon heating, can possibly approach the value that it was at manufacturer, but, probably not quite back on value. YMMV Glenn On 11/30/2020 8:22 PM, Bob Albert via groups.io wrote:
I don't think the procedure for proper measurement of resistance would have an appreciable effect on a resistor that is grossly out of specification.? Maybe for nitpicking whether it's in spec or not, but not for gross errors. --
----------------------------------------------------------------------- Glenn Little ARRL Technical Specialist QCWA LM 28417 Amateur Callsign: WB4UIV wb4uiv@... AMSAT LM 2178 QTH: Goose Creek, SC USA (EM92xx) USSVI LM NRA LM SBE ARRL TAPR "It is not the class of license that the Amateur holds but the class of the Amateur that holds the license" |
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On Tue, Dec 1, 2020 at 11:10 AM, Richard Knoppow wrote:
This is not really replying to Richard... but, just mostly reiterating what I previously claimed about carbon composition resistors. We have hundreds of IRC SR series 2W fixed carbon composition resistors. These are more than 5 decades old. They are painted as Orange Black Brown Gold and so have, Nominal value: 300 ohms, Nominal Range: 285 to 315 I measured 10, taken at random, from the box. 333,322,337,321,339,315,334,314,314,329 Are these resistors way out of spec.? I wouldn't say so, given the uses to which they are properly put. They are more like silver banded (10%) than gold. If you notice they all measured 315 ohms or greater. This I knew was almost certainly the result of "moisture" absorption. After time in the oven, they mostly measured to be less than 315 ohms... and so mostly back in spec. The original MIL spec. for these resistors was MIL-R-11C, which is long obsolete. Table XII "DC Resistance Test Voltages", pg.13, of MIL-R-11G give the voltages different values of carbon composition resistors are to be tested at... to measure their resistance. MIL-HDBK-217F Section 8.1, page 9.2 gives the reliability of carbon composition resistors. |
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Maybe a new thread should be started, as this seems to have drifted (pun intended).
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But just to add to the noise, my statistically insignificant data is that high-value carbon comps tend to drift much more than do low-resistance ones. I would hesitate to declare a boundary between low and high, but it seems to be in the tens of kilohms. Roy's data is at least consistent with that. I would not have expected gross drifts with a 300 ohm resistor. But 300k? I would bet that a fair fraction would read as near open circuits. That also comports with the common problem with resistor strings in HV circuits (not just Tek's). --Tom -- Prof. Thomas H. Lee Allen Ctr., Rm. 205 350 Jane Stanford Way Stanford University Stanford, CA 94305-4070 On 12/1/2020 20:37, Roy Thistle wrote:
On Tue, Dec 1, 2020 at 11:10 AM, Richard Knoppow wrote:I wonder about improving stability by baking.This is not really replying to Richard... but, just mostly reiterating what I previously claimed about carbon composition resistors. |
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Tom Lee wrote:
I think that this thread has stayed remarkably on-topic, maybe even become more so as it aged. I'm absolutely fascinated by both the insight into the working (and failing) of what I always thought of as the second simplest element of any electronic circuit. I'm fascinated (and horrified) by the stories of how people trimmed such resistors in practice. -- Jeff Dutky |
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No question that it's been a very interesting thread. But as one who spends much of his life with search engines, I'm always sensitive to how well subject headings reflect thread content, hence the observation about drift. Future readers might well be interested in baking resistors and filing notches in them, but "Resistors in series" won't help them much to find such (horrifying, as you say) gems.
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-- Prof. Thomas H. Lee Allen Ctr., Rm. 205 350 Jane Stanford Way Stanford University Stanford, CA 94305-4070 On 12/2/2020 08:28, Jeff Dutky wrote:
Tom Lee wrote:Maybe a new thread should be started, as this seems to have drifted (pun intended).I think that this thread has stayed remarkably on-topic, maybe even become more so as it aged. |
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I might add that this thread started as an addition to another original thread:
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"Yes, this thread is a response to my thread "Fix or Part Out a 475A" and specifically is a discussion of the perplexing arrangement of resistors R1354 and R1356 across the collector-emitter of the Q1354 transistor in the beam intensity amplifier circuit." I have filed it under 475A, but the further discussion has little to do with the 475A. Colin -----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Tom Lee Sent: 02 December 2020 17:34 To: [email protected] Subject: Re: [TekScopes] Resistor in series No question that it's been a very interesting thread. But as one who spends much of his life with search engines, I'm always sensitive to how well subject headings reflect thread content, hence the observation about drift. Future readers might well be interested in baking resistors and filing notches in them, but "Resistors in series" won't help them much to find such (horrifying, as you say) gems. -- Prof. Thomas H. Lee Allen Ctr., Rm. 205 350 Jane Stanford Way Stanford University Stanford, CA 94305-4070 On 12/2/2020 08:28, Jeff Dutky wrote: Tom Lee wrote:Maybe a new thread should be started, as this seems to have drifted (pun intended).I think that this thread has stayed remarkably on-topic, maybe even become more so as it aged. |
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Okay, to bring this a little bit back to the original topic:
I received the first batch of replacement NOS carbon comp resistors today. I checked them with a multimeter and they all read a bit high: between 7.7 k¦¸ and 7.9 k¦¸, which is between 2.5% and 5% off. But these also appear to be marked at 10% tolerance (it's hard to tell if the metallic band is silver or gold), so that's still well within spec, and much better than the two that are in-circuit on the 475A. It's also hard to tell from the pictures I took of the circuit board ( /g/TekScopes/photo/257066/0?p=Created,,,20,2,0,0 ), but the upright resistors may not have any tolerance band, meaning that they are 20% tolerance, which would put them just within tolerance with their present measured values of ~9 k¦¸. The service manual, however, indicates that they are supposed to be 5% tolerance parts. I'm considering taking the lowest measured values and using them to replace the existing (drifted) parts, but it's going to be tough getting the iron in to de-solder them from the board. If I were going to "bake" some of these to see how that affects them, how would I go about doing this? -- Jeff Dutky |
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On Wed, Dec 2, 2020 at 01:19 PM, Jeff Dutky wrote:
If I were going to "bake" some of these to see how that affects them, howHi Jeff, An old Allen-Bradley fixed resistors catalog specifies the correct conditioning parameters. Here is a quote of the relevant section: Effect of moisture absorption - Moisture attraction is aI use a temperature-controlled oven, with a temperature sensor placed near the resistors on the rack. I set the oven controller to maintain 95 C. The actual temperature tends to vary +/- 3 C, which keeps it within 100 C. Also, an important aspect that has not been discussed in this thread so far is the effect of moisture ingress on soldering. Namely, it is my understanding that if there is any moisture trapped inside the CC resistor at the time of soldering, the high soldering temperature will cause this moisture to vaporize so rapidly that it can create micro-fissures in the resistor material, and especially near the carbon comp/lead terminal interface. Any such damage is permanent, and will then often get worse over time. The smaller the resistor, the more vulnerable it is to this type of damage. The small 1/8W carbon comp resistors that Tektronix used in high bandwidth equipment in the 60s and 70s (S- series sampling heads, 7S- and 7T- plugins, DC508, etc.) are _extremely_ fragile in this regard. I place the baked resistors in a hermetically sealed container immediately after baking is finished, and make sure to complete all soldering within an hour or two after that. I never attempt to solder CC resistors that may have absorbed moisture, and always use heat sinks during soldering. dan |
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