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Question re: capacitor in Tek 181
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What was Tek thinking? Capacitor C420 in the 181's schematic gets spec'ed as an electrolytic cap of
6.25 uF at 300 volts, -10%-+100% tolerance. It's filtering the -25-volt line, so 10 uF at 450 V should do nicely. as a replacement. I can't figure out why a Tek engineer would specify a nominal value of "6.25 uF", considering that electrolytics aren't that precise to begin with. Any insights would be welcome. Thanks, and 73-- Brad? AA1IP |
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Hmmm, they had a big box full of them?? Wouldn't be the first time that overstock got used like that.
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Harvey On 5/2/2020 11:08 AM, Brad Thompson wrote:
What was Tek thinking? Capacitor C420 in the 181's schematic gets spec'ed as an electrolytic cap of |
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On 2020-05-02 11:08 AM, Brad Thompson wrote:
What was Tek thinking? Capacitor C420 in the 181's schematic getsIn such a case I would assume that the original part was marked or sold that way and so it was the safest way to describe it. What are the markings on the part? Does the parts list give an expected tolerance? --Toby
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Hi Brad,
Another question is why C401, which has identical description as C430 and C431, (2x20uF, 450V, -10%, +50%), has a different part number. Maybe the Tek engineer was also a unique artist, like Leonardo Da Vinci, and wanted other engineers to stand in admiration in front of his designs asking themselves questions, like the public standing in front of the Mona Lisa ask themselves "why is she smiling?". My personal take on this is that if we wonder why some piece of equipment seems over designed or under designed, or over specified or under specified, we should not assume that there was some esoteric reason in the superior mind of the designer, but take it as some mundane oversight. And we are free to follow that detail or not. (stated by a former designer). Ernesto |
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Ernesto wrote on 5/2/2020 3:35 PM:
Hi Brad,Hello, Ernesto-- C401A and C401B are listed as 2X20 uF, p/n 290-036. C430 is listed as (2X20 uF), p/n 290-037 C431A and C431B are listed as 2x 20 uF, p/n 290-037 In the schematic, C430 appears as a single 40 uF capacitor-- it's connected in parallel with C431A 20 uF. Showing C430 as C430A and C430B (20 uF each) connected in parallel would clarify matters. As for C401 and C431 having two different part numbers, perhaps C431 gets prepped with an insulating cover (since its can floats at -150 volts with respect to the chassis) and hence deserves its own part number? From an engineering viewpoint, The "Mona Lisa" could have been painted on a smaller canvas for more efficient use of materials.<g> (Ear protection in place to muffle outraged howls emanating from artaficionados). Or as someone suggested, perhaps there were leftover 6.25 uF caps in stock. Never underestimate a buyer or purchasing agent's appetite? for shortcuts. I served as components engineer for a small (soon to be even smaller) company. One of the purchasers called me into his office and explained that a crystal manufacturer had mislabeled a batch of 14.7xx MHz crystals as 17.4xx MHz crystals and could we accept the lot as-is and just make a note in the schematic? I pointed out that the already beleaguered (*) field service engineers were struggling with a severe case of board float, and the only way that those crystals could be acceptable would be if the manufacturer took back the lot and applied shrink-wrap sleeves marked with the correct frequency on each crystal. The buyer didn't want to "bother" the manufacturer-- after all, only 100 parts were involved and couldn't I be a little more flexible? No, I couldn't and the whole g----ed lot is hereby rejected. 73-- Brad?? AA1IP Beleaguered (n):? a 16 by 16-inch, six-layer boards with approximately 120 ECO cuts and wires. |
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Hi Brad,
A while ago I received a private message from Dan G. to make me aware that the can of C401 is floating at a negative supply. I appreciate very much his use of the private message to avoid embarrassing me here for having overseen this important detail, even when at my age I have lost all shame, ha ha. I had assumed, without certainty, that C401 is the same part as C430 and C431 just mounted on an insulating sleeve. But there are no drawings in the maintenance manual, and I could be wrong. I was always the project designer engineer, and someone else did the product engineering. There was always collaboration, but different perspectives. This is why I can easily be wrong in my opinions here. Ernesto |
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Brenda
Sorry that I am late to this thread, I had a really busy day!
I don't know, I think some of the folks on here are right, that it may have just been an overstock and they decided to use this value. But either way, 6.25uf is a very odd value as capacitors back in the day were not that precise. But since I do not have a printed manual (I prefer printed manuals over pdf's), and I am sure that Brad is right, I am just wondering if a 450V capacitor is overkill, maybe a 50V or 250V 10uf would be more sensible. Or maybe I should use the 450V and have that nice big headroom. Brenda |
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Might have been a timing capacitor they had a lot of, hence the very precise value.
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Me, I'd give it about 100 volts headroom.? Then again, I tend to overdesign stuff. Harvey On 5/2/2020 9:08 PM, Brenda via groups.io wrote:
Sorry that I am late to this thread, I had a really busy day! |
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Part of the schooling for junior engineers at Tek was strong encouragement to use the Common Design Parts Catalogs. I think I was told it cost $10000 of overhead to add a new part, so if you asked for one, you'd better be ready to prove that nothing there would do.
Dave Wise Information Display Division, 1980-1995 ________________________________________ From: [email protected] <[email protected]> on behalf of Brad Thompson via groups.io <brad.thompsonaa1ip@...> Sent: Saturday, May 02, 2020 4:25 PM To: [email protected] Subject: Re: [TekScopes] Question re: capacitor in Tek 181 Ernesto wrote on 5/2/2020 3:35 PM: Hi Brad,Hello, Ernesto-- C401A and C401B are listed as 2X20 uF, p/n 290-036. C430 is listed as (2X20 uF), p/n 290-037 C431A and C431B are listed as 2x 20 uF, p/n 290-037 In the schematic, C430 appears as a single 40 uF capacitor-- it's connected in parallel with C431A 20 uF. Showing C430 as C430A and C430B (20 uF each) connected in parallel would clarify matters. As for C401 and C431 having two different part numbers, perhaps C431 gets prepped with an insulating cover (since its can floats at -150 volts with respect to the chassis) and hence deserves its own part number? From an engineering viewpoint, The "Mona Lisa" could have been painted on a smaller canvas for more efficient use of materials.<g> (Ear protection in place to muffle outraged howls emanating from artaficionados). Or as someone suggested, perhaps there were leftover 6.25 uF caps in stock. Never underestimate a buyer or purchasing agent's appetite for shortcuts. I served as components engineer for a small (soon to be even smaller) <snip> |
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A sure sign of too many layers of bureaucracy
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Steve -----Original Message-----
From: [email protected] <[email protected]> On Behalf Of Dave Wise Sent: Monday, May 4, 2020 11:52 AM To: [email protected] Subject: Re: [TekScopes] Question re: capacitor in Tek 181 Part of the schooling for junior engineers at Tek was strong encouragement to use the Common Design Parts Catalogs. I think I was told it cost $10000 of overhead to add a new part, so if you asked for one, you'd better be ready to prove that nothing there would do. Dave Wise Information Display Division, 1980-1995 ________________________________________ From: [email protected] <[email protected]> on behalf of Brad Thompson via groups.io <brad.thompsonaa1ip@...> Sent: Saturday, May 02, 2020 4:25 PM To: [email protected] Subject: Re: [TekScopes] Question re: capacitor in Tek 181 Ernesto wrote on 5/2/2020 3:35 PM: Hi Brad,C431, (2x20uF, 450V, -10%, +50%), has a different part number. Hello, Ernesto-- C401A and C401B are listed as 2X20 uF, p/n 290-036. C430 is listed as (2X20 uF), p/n 290-037 C431A and C431B are listed as 2x 20 uF, p/n 290-037 In the schematic, C430 appears as a single 40 uF capacitor-- it's connected in parallel with C431A 20 uF. Showing C430 as C430A and C430B (20 uF each) connected in parallel would clarify matters. As for C401 and C431 having two different part numbers, perhaps C431 gets prepped with an insulating cover (since its can floats at -150 volts with respect to the chassis) and hence deserves its own part number? and wanted other engineers to stand in admiration in front of his designs asking themselves questions, like the public standing in front of the Mona Lisa ask themselves "why is she smiling?". From an engineering viewpoint, The "Mona Lisa" could have been painted on a smaller canvas for more efficient use of materials.<g> (Ear protection in place to muffle outraged howls emanating from artaficionados). seems over designed or under designed, or over specified or under specified, we should not assume that there was some esoteric reason in the superior mind of the designer, but take it as some mundane oversight. And we are free to follow that detail or not. (stated by a former designer). Or as someone suggested, perhaps there were leftover 6.25 uF caps in stock. Never underestimate a buyer or purchasing agent's appetite for shortcuts. I served as components engineer for a small (soon to be even smaller) <snip> |
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