HP 5245L Nixie Counter - Part 6: HP 5255A 12.4 GHz Plugin Repair

We repair a 12.4 GHz Nixie frequency counter plugin, the HP 5255A. It takes a double length episode to get it to behave, and you won't believe what we find at the end.
5245L Repair-a-thon Playlist: • HP 5245L Repair-a-thon
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00:00 Summary of previous episodes
00:53 The very broken 12.4 GHz plugin
02:19 Operating principle (with elevator music)
06:30 Opening the unit
09:35 Faulty video amp?
12:53 Debugging the Automatic Gain Control
15:48 Debugging the bias
17:32 RF self-oscillation hell!
22:11 Nursing the amp back to life
25:00 Debugging the power meter circuits
32:45 Debugging the gate extender
37:56 Finally measuring microwaves!
39:20 Discovery of another video amp issue
42:12 Debugging the weird low frequency suckout
47:37 Plot twist: RF mixer surprise!
52:22 Did we finally repair it?
55:42 Epilogue: comparing with another plugin

[@grahamjenkins1236]

"I went to the flea market and there was this guy selling plugins..." You must be living in paradise!

[@TrimeshSZ]

Those 12.4GHz plugins were famously unreliable and were generally fixed by swapping subassemblies. My guess is that the front end got blown up and the other bad modules were swapped in because it was dead anyway and it was quicker and simpler than doing component level repairs. Then at some point when it was being finally written off it was reassembled using whatever screws they could find just so it looked like a complete unit.

[@CuriousMarc]

Yes, that was clearly a parts unit that was reassembled to sell on eBay to an unsuspecting CuriousMarc...

[@afberglund2764]

Sometimes in the seventies?

[@TrimeshSZ]

You would be surprised how long a lot of this stuff hung on, especially in companies that were dealing with federal contracts. I can remember using that counter and plugin in the mid '80s - because that was what was called out in the test procedure, and as long as you had a working unit it was easier to just use it than change the documentation. Some other instruments (like the HP8640B signal generator) were still in use in the '90s for certain applications because they were integrated into test setups in a way that made them very hard to replace. @@afberglund2764

[@zyeborm]

@@CuriousMarc The one you repaired does match the colour scheme of the counter though so it's got that going for it, which is nice ;-)

[@CuriousMarc]

@@zyeborm I like that positive way of thinking. 1960 colors for the win!

[@JensAndree]

As someone who's never really taken a dive into the pool of analogue electronics (I'm foremost a SW engineer but I dabble in digital electronics) - these vintage electronics repair videos are awesome and would you know but I now have a much greater understanding of RF after following you for all these years... Also we who are watching these videos have a much longer attention timespan than ~10 minutes so don't worry about making short videos - in fact please do more 1+ hour videos! I'm sure people here will agree. $5 for that plugin surprised me but I guess there aren't many buyers out there, hence the very low price. Can't even buy a beer for that in my neck of the woods... Thanks for keeping all that hardware alive for the future generations - and for sending less electronics to the landfills!

[@MichaelOfRohan]

This man speaks the whole truth

[@TooMuchMiddle]

Agree with the longer videos! I really love it when you go deep into a project.

[@johnvanantwerp2791]

Yeah, you can do a lot even on modern electronics. Our TV crapped out 10 years ago and I was told I'd have to get a new one. Instead of spending $800 on a new TV, I broke out the meters, replaced 2 $4 caps, and it's worked great for the last 10 years...

[@MichaelOfRohan]

@@johnvanantwerp2791 absolutely. I did the sams with my Xbox One psu, totally crapped the bed audible power surge on every boot followed by hard crash. 4 1600uf caps later and ive got over 100 hours of uptime since. FIX. YOUR. OWN. STUFF.

[@williamsquires3070]

Yeah, we might need it to go back to the moon again. Or even relaunch modern civilization after a nuke attack. You just never know.

[@chuck10088]

That 1 hour went by quick. Don't be afraid to put out a longer video. It's almost 3 AM here, guess I better get some sleep. Thanks for the great content. (BTW $5.00 for a plugin, wow to think how much it cost in1966)

[@markweingart7636]

I agree, same here

[@leandrolaporta2196]

probably like a small house? hehe

[@CuriousMarc]

Well, we can get the price straight from the 1967 catalog: HP 5245L base unit: $2950, which in 2023 dollars is $27,000. And the HP 5255A 12.4 GHz plugin: $1650, which is $15,100 in current dollars. I think I got a good deal on the 2nd plugin...

[@rav3nx33]

Loved the long video. 👍 worth doing every now and again. Thanks Marc, love your work 😝

[@gregkrekelberg4632]

@@CuriousMarc In 1967 dollars, you paid roughly 55 cents for the second plug in!

[@neilbarnes3557]

Ah, for a return to the days when HP equipment was designed to work and be repairable for fifty years, and not e.g. stop scanning because the attached printer has the wrong sort of ink in it. Oh well, at least my HP calculators still work, complete with RPN operation that stops anyone ever borrowing them twice :D Nicely done, Marc; nicely done.

[@stargazer7644]

The HP that made that test gear and the HP that makes those printers are not even remotely the same company.

[@zh84]

You've been watching Louis Rossmann too, haven't you?

[@musiqtee]

This is “true crime” for me - fantastic! As a mere tech (audio), I’m childishly proud of one detail that I guessed right. At the very start when the video amp was acting up, the “magic finger” probing gave it away - failing or no isolation beneath the board. To me that was 10 tense minutes until you pointed that out. The studio I worked at had a HP scope and a generator (like yours), but what tickles me most is that Weller soldering station. Man, I had to put in hundreds of hours through the years using the same one. You and your team do admirable and important work, besides the video documentation. Best of luck, and huge thanks from 🇳🇴!

[@mikebarushok5361]

That point where the missing diode only allows functionality by unhooking the corresponding signal at the other end and your mentioning it being like an 8 cylinder engine that is running on 4 cylinders took me back to a high school memory from around 1974. A friend of mine was in his Karmann Ghia waiting for the traffic light to change and we stopped behind him. I jumped out, opened his engine compartment and pulled a spark plug wire loose, nothing, no change. So I pulled another one and yet it idled fine. The lights changed and we followed him back to school and when he got out he wanted to know what I did to make his engine run better. Turns out that engine ran better with only two cylinders firing than with two spark plug wires reversed. Purely a coincidence that I pulled the two reversed wires loose.

[@MichaelOfRohan]

Hahaha i know about getting the plug wires in the wrong order, isnt a couple of the wires the same length or something? Who knows how hard it was on the engine firing at the wrong time.

[@mikebarushok5361]

@@MichaelOfRohan I suspect that they were aftermarket plug wires and all the same (and excessive) length. It's not unusual that reversing two plug wires results in firing during the exhaust stroke which does result in the piston seeing force in the wrong direction, but with the exhaust valve open. Not good for bearings, connecting rods or power. But no where near as bad as firing during the compression stroke.

[@c1ph3rpunk]

And I thought my floppy controller was kicking my rear, boy this one has been a pain. 12.4 GHz? Wasn’t that like ALL the hertz at the time? No wonder it hertz so much to repair. ;-) Big red writing “do not attempt to disassemble cavity”. Marc: let’s disassemble. :-)

[@MVVblog]

I'm directing all the skeptics who don't believe in the Apollo missions to this channel. I don't expect them to change their minds, but there's always hope for everyone.

[@johnopalko5223]

I recently read a comment on another channel where the person was convinced the moon landing was faked because, after all, how did they live stream from the moon before the Internet? I hope they were joking but, sadly, I suspect they were serious. I thought about directing them to Marc's explanation of the Apollo video system but decided it probably wasn't worth the effort.

[@user-sd3ik9rt6d]

Longest video yet? you are spoiling us.

[@cleaneraz09]

Not gonna lie.. i will keep this video until my child go to sleep and I will enjoy every single second of it!

[@pjelbro3492]

A coax cable which is open circuit one end will appear as a short circuit at the other when the length of the coax (including velocity factor) is a quarter wavelength. It's a fundamental feature of coax cables used as quarter wave transformers although that is not the intended use in this case. A reminder of the many hours spent troubleshooting circuit boards of different types over the years. Great video. Thank you

[@MatthijsvanDuin]

Not just coax cables but transmission lines in general

[@pjelbro3492]

... and waveguides and quarter wave coatings on lenses to make them anti-reflective. The refractive index of the coating is the square root of the RI of air (~1) times the RI of the glass substrate.

[@larryscott3982]

I love HP kit. But not like Marc. He’s having such fun. Returning 60s and 70s HP instruments to service is fantastic

[@TheEmbeddedHobbyist]

Thanks for making the documents available on line, it's great to be able to download the circuits and play along at home. I love longer video's as I've got lots of time, and your never too old to learn. Used up to 18GHz in our test chamber but never looked at how the older equipment got around the limitations of the components.

[@andymouse]

The long videos are great !....squeak !!!!!

[@TheEmbeddedHobbyist]

Well hi @@andymouse

[@karlpron]

Not only to repair it but to make it better? That's Marc for you. Great video. Thanks.

[@ReneSchickbauer]

I always especially enjoy the parts when modern components are TOO good and it turns out the engineers in the 1960 used some of the design/manufacturing problems of their components to make the circuit work. A bit like a car engineer going "We can't make the rev limiter work, but it's fine. The carburator is so crappy that it will NEVER go above 5000 rpm anyway.".

[@L0wcash]

So satisfying to watch your video's Marc! When you said 'wish me luck' when opening the microwave cavity i really was on the edge of my seat and wishing we'd see the cause of the dip! Better than any murder mystery! Thanks for your entertaining and very educational video's!

[@erikdenhouter]

Cutting off half of the dark magic, and it still works, THAT'S dark magic. Very nice fault finding. I could almost swim beside you, but as soon I am alone I sink like a stone ☺

[@aceweldon6926]

Ty for the extra long video! Now I don't have to click a new video for an hour. Thank you for the treat.

[@TheGunnarRoxen]

Your videos are great, Marc. I love the deep dives, the electronic archaeology and the repairs. I'm learning so much, thank you.

[@harmlesscreationsofthegree1248]

It always heartens me to catch a glimpse of that lovely Juno in the background 😊 you are a man of infinite taste, sir!

[@stefanmadsen5605]

an absolute treat, sitting on the edge of my seat to debug the problem myself as you go along, and boom - missing component :)

[@albinklein7680]

I have a masters degree in E.E. but this multi-GHz black magic stuff is still beyond me. When wiring turns into plumbing, I am out. A friend of mine, who graduated in the same year (1993), works for a company that makes radar sensors for range finding, automatic doors and self flushing urinals (lol). When I see his ceramic substrate prototype boards with those weird and gold plated geometric shapes and randomly placed metal blocks with hundreds of randomly placed screws in them (yes, of course I know that there is nothing random about it...), I think of some kind of demons you have to worship to be able to understand that...

[@neilbarnes3557]

RF engineering is all about having sufficient chickens and goats for the necessary sacrifice...

[@leandrolaporta2196]

"when wiring turns into plumbing" HAHAHAHAHA ROTFL 🤣🤣, it's like he says "the black art of electronics engineering" indeed

[@ReneSchickbauer]

@@neilbarnes3557 I'm a software dev. A fellow dev once said to me: "It really depends upon your project’s DFQ (Dissected-Frog Quotient), followed by your cauldron-burn and fire-bubble.". I think that might be the closest equivalent to RF magic i'm getting in my line of work.

[@henryD9363]

Microwave engineering is more like musical instrument engineering. Wind instruments violins things that vibrate based on what they're made of, how big they are, etc

[@dabyd64]

Agreed! Fixed a RF pulse generator, it was relatively easy until the 2ns setting. The 1ns did some rf black magic with several loops in a ceramic substrate. The solution was adding a label: "Works*" (Up to 2ns)😂

[@peep39]

My favorite thing about your channel is my endless amazement at 1960s technology. I was born too late

[@zxborg9681]

Great video. The debug takes however long it takes to resurrect the unit, the video takes however long it takes to tell the tale. So great to see these old units brought back to life. Back in the 80s I used to have a collection of 50s/60s tech, watching this makes me nostalgic that I should have held on to it all.

[@hymermobiler]

Another fascinating video repairathon Thanks Marc. I dont care how long your videos are Im glued to them from start to finish!

[@spiritualreality7890]

What I would do about the insulation under the screwed down board is find a thick nylon or tough red paper and make one, you could have it done on a laser cutting to cut the insulation and get factory look insulation. The metal standoffs is very shallow! But good job on getting the electronics thief mystery solved. :) What a good show.

[@medicman4444]

Oh Mark I love your videos it's 6:59 a.m. I haven't want to sleep yet You've dropped this and I'm sitting here worrying with myself to watch the whole hour long video or to go to sleep 😂 I may have to rewatch tomorrow If I'm sure the elevator music will claim my sleepiness😅

[@Dirk-Ulowetz]

Thanks to Usagi Electric for recommending this channel. Love this content. Subscribed immediately. 👍

[@KeritechElectronics]

The other kind of AGC :) A magnificent work of electronic engineering. Coming from the audio and broadcast receivers world, RF electronics is pretty advanced stuff already, and anything that goes over 1GHz is black arts, haha!

[@msylvain59]

Lesson learned, next time just go in a fleamarket with 5 bucks 😂

[@AmiPurple]

Oh boy, the day got better with a curiousmarc video! Thank you lots for an entertaining and informative video. Hope you have an awesome day

[@leandrolaporta2196]

man you don't disappoint, this video was freaking fantastic!, one hour of pure GOLD, and also i learn a few things i had no idea!, thank you!

[@joopworst]

Best video yet! When it comes to your repair video’s; the longer the better!!!

[@nikmilosevic1696]

That was an epic episode, thoroughly enjoyed this!

[@pete3897]

In chapter 3 operating principals I got serious dejavu from the recent 100Ghz Signal Path video :)

[@5cyndi]

This is one I’m going to rewatch tonight. Awesome work of troubleshooting!

[@bin_chicken80]

It's great seeing you work through these problems Marc. Always learning from your videos. Thanks!

[@BarryRowlingsonBaz]

The one you repaired has a much better colour match to the main unit than the "working" one!

[@CuriousMarc]

Yes! There was a change in color in the 1970's that ushered in the Age of Beige, moving away from the post-war gray to the cream colored theme. The main instrument has the 1960's gray which matches the older plug in. The one I got at the flea market must be from the 1970's and has the cream color, which would have matched a main instrument from the same date. The plug in from episode 5 is also has the Age of Beige theme.

[@wonderbars36]

Ah this is fantastic, Marc. Getting into Signal Path land with the RF now lol. Both you and he absolutely crush it on repairs. These are so challenging in what they present you with and also just so cool to watch. Wonder if he also watches you (Shahriar)? I figure he'd love this one. Anyway great work man. Love the longer videos too.

[@guyh3403]

The ease in which you read the schematics is astounding. Thank you so much!

[@danielatbasementtech]

As always, simply fascinating… the black art of analog electronics on the bleeding edge.

[@RicoD5]

“Here goes the longest repair video yet. So jump around using the chapter thingies”… Naaah, think not! No way I won’t watch this in one go 😊

[@Ray-ej3jb]

Loved the longer video

[@rsmrsm2000]

Incredible ! Every time you see better. Thank you for that.

[@ducksonplays4190]

This one is going to be fun!

[@CuriousMarc]

You tell me in an hour... The end is quite a plot twist.

[@Bobbias]

@@CuriousMarc Just remember your viewers may have a different definition of fun than you :)

[@CuriousMarc]

Nah. We all adore chasing arcane bugs, only to find at the end that someone evil purposely planted and hid the fault in there. That IS the definition of fun on this channel!

[@Bobbias]

Oh my, that was a sneaky fault!

[@ducksonplays4190]

@@CuriousMarc It was too late for me to watch it last night, but that is some sneaky problems! A piece of cardboard and a missing diodge!

[@islandhopperstuart]

Just brilliant work Marc! Loving the deep detail of these videos, and in awe of your skill and perseverance. Now when's the next HP electronics flea market in the UK?

[@websterleone]

A really good video, was quite a journey to figuring it out. I also appreciate how little noise from moving the camera there was for how long the video is. I have hearing sensitivity and those sorts of sounds drive me up the wall so I appreciate the extra work to prep between shots.

[@tekvax01]

Doctor Marc, another amazing repair!

[@gilmartrevisan]

You do an amazing job. Congratulations.

[@mumiemonstret]

56:36 is so funny and true... One's trash another's treasure. I saw a KZbinr dig up a C64 from the mud and restore it, knowing that perfectly working ones are thrown away because the owner won't bother selling them for a couple of bucks.

[@keresztesbotond740]

Here is a conspiracy for you: What if the newly acquired unit is also missing a diode and that's why they are performing similarly? We may never know :D

[@CuriousMarc]

In fairness I haven't checked, but it would also have the dip, which is not the case. Both instruments are way more sensitive than the spec by the way. But what's an internet without conspiracies?

[@zeevo]

@@CuriousMarcnot if the same terminal is disconnected!

[@erickvond6825]

I sense a growing addiction here. I approve...

[@martinhughes8500]

Oh, how I need you to repair my two Telequip DM63s. I am a retired engineering technician and have difficulty recognising typical transistor configurations. I just don't have the experience or training. But you've inspired me to have another go.

[@DonKees]

Wonderful Video! Just a brief comment on 24:42: HP 8444 Tracking Generator with option 59 is needed for operation for 8567A & 8568B Spectrum Analysers. To develop a 100 Hz to 1500 MHz tracking signal for an 8568A/B Spectrum Analyzer system, a 2.05 to 3.55 GHz First LO is available from the 8568A/B, but no 500 MHz LO is used in this instrument. Option 059 consists of a 500 MHz oscillator for the 8444A. This 500 MHz signal is brought out on a separate BNC connector on the rear panel of the 8444A, directly above the THIRD LO INPUT BNC connector. When the 8444A is used with an 8568A/B Spectrum Analyzer system, the two rear panel BNC connectors are interconnected with a short BNC cable. With the First LO from the 8568A/B plus its own 500 MHz LO signal, the 8444A with option 59 can provide a 100 Hz to 1500 MHz tracking signal for the 8568A/B Spectrum Analyzer system. Note if you have a HP 8444 without option 59 an external 500 MHz source can be used to input -3 to -4 dBm @ 50 Ohm into the THIRD LO INPUT.

[@Hans-gb4mv]

Sold a lot of those, have you? 😉

[@ATOMSHAMRADIO]

Old technology is cool and a art⚡👍

[@paulw3182]

A detailed analysis, great job!! What a pain to repair - what patience! What a find at the flee-market, hopefully next time you could trip over a unloved AGC? :)

[@psy0rz]

Very impressive repair!

[@aussiedazvk4djh889]

Well done Marc

[@ToTheGAMES]

Love the long video's!!!

[@peteroneill404]

I'm jealous that to have a local flea market selling this type of gear. I only have some of the plugins you've shown here, which I can run in my 5245L, I'm looking for an HP10536A adaptor so they can be used in my HP5360A computing counter.

[@kombi9648]

Love longer videos.

[@andymouse]

Long format FTW !!!.....cheers.

[@Egam]

The last 5 dollars already working module would have prevented us from seeing this repair quest that we definitely enjoyed.

[@michaelturner4457]

1963, the year I was born 😊

[@CuriousMarc]

Congrats, you are vintage, just like me!

[@Hans-gb4mv]

I knew there was a place on the internet where I can feel young again 😀

[@williamsquires3070]

Next, Marc will dig up the transwarp engine chips Scotty took out of the Excelsior’s warp drive, and will use them to repair some HP test gear. 😊

[@ForOurGood]

Who could have guessed, missing cardboard and missing diode.. Someone really messed with that thing! Seeing you tie yourself in knots, going down the wrong path is therapeutic, makes me feel better when I do the same..😂

[@camhyde9701]

Really solid content Marc... opening music is in Ab =)

[@ATOMSHAMRADIO]

God i love nixie tubes

[@MarcelHuguenin]

Fathinating...utterly fathinating ;-) You really must enjoy working on this old equipment, spending so much time for it to finally succeed and even improve the equipment as you did this time. So much educational value for us and even more enjoyment. Thanks a lot.

[@analogdesigner]

Wow, this is known as a "Case of Beer" project!

[@andersslangerup7464]

Good job

[@Hans-gb4mv]

repair-a-thon he said ... no kidding 😯 And if the second unit does have the missing diode, transfer it, at least you'll have a fully functioning one with matching color faceplate :)

[@protox07]

I like your videos

[@ATOMSHAMRADIO]

Wow thats crazy and cool😮

[@LachlanWetherall]

Thanks!

[@CuriousMarc]

Well thank YOU!

[@vincei4252]

Yeah, I am fully aware of the awful Keysight scans. I need to repair my HP8563E and the scans I found there made me want to cry.

[@MrThomashorst]

No one at my local flea-markets offers such gear ... think I choose the wrong location to settle down😂

[@MeriaDuck]

When everything seems to work and there is still 20minutes of video to go...

[@EricLikness]

49:55 "Not recommended for field replacements", but they never anticipated curiousMarc and his magical lab and collection of vintage HP parts. 👍 and it was a missing Microwave diode the whole time.

[@zyeborm]

I don't think you could call his lab the field any more ;-) it must be more like HP heaven, where well behaved test gear goes after it has died.

[@paulkocyla1343]

Wow, having that on the bench in the 60ies would have been pure Voodoo. In a time where most people knew computers only from movies or books. This high frequency was not accessible by amateurs I guess - or was it? It´s kinda hard even today!

[@CuriousMarc]

Indeed, microwaves was mostly out of the realm of amateurs. A few hams did manage to listen in to the Apollo 2.1 GHz S-Band voice, but if you look closely, they were all affiliated with some professional or academic microwave research lab, and "borrowed" the critical pieces of front-end microwave equipment, usually the microwave antenna, receiver and mixer, then worked on the IF with regular ham radio stuff to complete their receivers. This was squarely aimed at space/military coms and radar.

[@stargazer7644]

The first amateur 10 GHz contact was made between W2RJM and W2JN over 3km in 1946. By 1960 the record for a 3cm contact was already 460km. Quite a few hams are active in microwave now, up through 250 GHz. Icom even sells the IC-905 which (with options) will get you on 1.2, 2, 5 and 10GHz right out of the box. It isn't hard, just expensive.

[@landspide]

I wonder if the video amp pcb actually relied on the pads under the screws to actually complete the circuit. Crazy that the tolerances were so close that torquing them down shorted out with the enclosure.

[@SpeakerNoise]

Salut Marc and the entire team! I wonder if it is possible to figure out how much this gear costs back in the days and what one have to invest in todays money. Those can‘t be cheap!! Many thanks for your great content and explanations.

[@624Dudley]

I want to be Marc when I grow up. 👍

[@tlrptg]

maybe the other module has a dead diode too. But good thing is that you can make a perfectly functional unit this way.

[@broklee]

31:47 When can we expect a video of the Roland Juno 6/60 in the background?

[@CuriousMarc]

It needs to break first...

[@douro20]

I wonder if a plugin could be made with a CMOS wideband synth or a YIG oscillator?

[@stephenbell9257]

I hope you are going to test the 5257A Transfer Oscillator as well so we can see the 5245L measure all the way up to 18GHz!

[@CuriousMarc]

Yep, it's coming in the next installment. And guess what, it is broken too...

[@zyeborm]

@@CuriousMarc Is it bad for us to get so much joy from your stuff being broken?😁

[@CuriousMarc]

@@zyeborm Certainly not! I enjoy them more when broken too!

[@zero0ryn]

You've modified the circuit to compensate for the fault. :)

[@RemcoStoutjesdijk]

I fear what happens when your stack of 60s era superfast NPNs finally runs out

[@keresztesbotond740]

"Stay tuned for the next episode, where we'll be making homebrew 60s era superfast NPN transistors" - Marc in 3 years probably

[@Broken_Yugo]

Spot weld leads on available SMD parts.

[@tony359]

Boo "technician from hell" :) Amazing episode!

[@TRBORADIO]

I have the answer, that HP piece of equipment was fixed by a Marconi's technician :):):)

[@TradieTrev]

Suck s mad dog!! You inspire all my nerd skill!!

[@SeanBZA]

Miss the fancy pants intro.......

[@ziggfreud9820]

Unless the newer one is missing a diode too!!

[@cambridgemart2075]

It is so annoying that when buying old HP equipment that would have shipped with manuals that had all the technical descriptions, schematics, layouts, and BOMs, the manuals are almost always missing. I guess they are in an alternate universe with all the missing socks!

[@FavoritoHJS]

first thing i thought of when seeing 12ghz is whether this has a high enough bandwidth to register that thing that computers and other such clocked appliances do to minimize rfi... what was it?... oh right, spread-spectrum clocking.

[@bigsarge2085]

✌

[@jonathanhendry9759]

Why is it called a "video" amplifier? Also is there a name for that dimpling pattern on the sheet metal? Anyone know why it's used? I've seen similar grids of tiny dimples on sheet metal in other devices.

[@stargazer7644]

Wideband amplifiers were called video amplifiers, because that's often what they were used for. The dimpling is usually done to make the material stronger or to make it look better.

[@ReneSchickbauer]

RF black magic. A butterfly flaps its wings on the other side of the planet and the slight change in capacity makes another component in your circuit go slightly out of spec and ruin your day.

[@kombi9648]

Should do more lives