HP 410C Vacuum Tube Voltmeter Restoration

Another classic Hewlett-Packard instrument saved from the trash bin: the HP 410C VTVM (Vacuum Tube Voltmeter).
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[@jeremiefaucher-goulet3365]

28:06 "There's an adjustment for infinity" This is next level god-like powers being able to set infinity at a specific fixed value. Marc is the Chuck Norris of Ohms.

[@av8bvma513]

But can he adjust my Nadir?

[@acmefixer1]

Did you know there are many infinities? That's what the theoretical mathematicians say.

[@jeremiefaucher-goulet3365]

@@acmefixer1 yes. Some infinities are bigger than others.

[@miroslavstevic2036]

@@jeremiefaucher-goulet3365 We can not say it like that. Some infinities are different, not bigger then others. Infinity multiplied by finite still equals infinity. So there is only one infinity in that sense. But there are different types of infinities. For example, infinity in complex numbers is not the same as integer infinity. Or, infinite time is not the same as infinite space. What is bigger, infinite time or infinite space?

[@CuriousMarc]

Thanks I feel better and more powerful already.

[@janosnagyj.9540]

Rewinding that zapped primary is a lazy weekend's job 😅 It might be another episode for us as well 😉

[@mrnmrn1]

Not if it is potted with epoxy. The laminated core could be a nightmare to de-laminate. But worth a try. If the same size transformer core is available, might worth cutting the old one apart with a grinder, count the number of turns and build a completely new transformer for it.

[@searchiemusic]

i appreciate you utilizing your accent for the spongebob joke

[@TechGorilla1987]

Consistently some of the fastest-passing content on the 'Tubes. It could be an hour long and the only thing I would change is to pop some popcorn.

[@CuriousMarc]

Thanks!

[@ragrabau]

And another example of why HP was always considered some of the best test equipment money could buy. Thank you Mark for saving another piece of electronic test equipment!

[@EricLikness]

Truly the HP gear takes a licking and in the right hands (schematics, parts and experience), they keep on ticking, scoping and measuring. 👍

[@fabiog801]

Hi Marc, i just want to tell you this : i am an italian craft brewer who lives in argentina with ZERO knowledge of electronics but still i find your videos 90% understandable and strangely very interesting to me. I followed the channel for years. Today i thought that this fact is totally odd and you deserved to know it. I really admire the thought process you follow. How you solve problems without getting stressed.. oh and you wotk with geniuses. The guy with the white coat who can reverse engineer everything. And the kid that made the rope core memory reader is over the top. Dude i cant fix my fridge.

[@CuriousMarc]

Wow, and thanks for the kind words! You’re just like me. I have zero knowledge in beer, but I like it very much!

[@TomKappeln]

"This transformer is imposible to find ..." Buys original Apollo and Aircraft parts ...

[@vincei4252]

"If you are dumb enough to short out the fuse ...." Words to live by.

[@mathewmcgill6266]

During my early career in the Air Force, I use to calibrate and repair those meters. The red push button switch should light up when on. HP was the world standard for quality equipment. Damn near all the equipment were either Hewlett Packard or Tektronix. I wanted to cry when it was relegated to a company that manufactured cheap printers.

[@CuriousMarc]

I’m crying with you!

[@johntomassetti3818]

Marc, I am a transformer engineer. I would be happy to reverse engineer the damaged power transformer for you. Let me know.

[@PsRohrbaugh]

We need to make this happen! Marc please contact him!

[@TheCanadaboy25]

I would love to see a video on that. Hopefully Marc takes him up on his offer!

[@gutschke]

I was surprised how inexpensive it can be to buy a custom-wound transformer. A couple of years ago, I needed an unusual combination of voltages in an unusual form factor. On a whim, I reached out to a vendor on EBay who offered a couple of different models that were close but not perfect matches. And it turned out they were a small outfit in China that didn't mind building me a transformer to order. Maybe, I just got lucky, but I didn't pay more than I would have had to pay for any COTS transformer and got exactly what I needed. I realize that there are a ton of parameters that can be tweaked when designing transformers. So, depending on what exactly needs to be done here, things could be more complex than merely enumerating the expected voltages. But it certainly is worthwhile looking into.

[@arjovenzia]

Transformers are pretty neat widgets. I had a passion project to build a tube amp, output transformers are heavy, vacuum tubes weigh less than air. So I figured roll your own, cos I found a motor rewind shop with a crusty ol Elmer. He knew motors n windings n ratios, I knew enough electronics to be pretty dangerous. Neither of us knew much about valves. But we got it working very well

[@twotone3070]

I wanted Marc to say that they were going to rewind the Xformer.

[@jlwilliams]

I like to think that this weekend at the Old Engineers' Home there's some old red-faced guy looking extremely embarrassed because his buddy just pulled up the CuriousMarc channel on his tablet and said, "Hey, Delbert, remember that time you smoked two HP VTVMs because you were too lazy to wire up the right probes?"

[@TB-nz4kf]

It was great to see these meters show up on the channel. Them came from the Fisher plant in NY when they shut down in the 70s or 80s. They were then stored in NJ for some time if I recall correctly. The owner then move to FTL where they were store in a loft for more that a few years. His company was being sold around 2016 so the EQ had to go. They gave the EQ to people that would promise not to sell it, but move it along to others as time goes on. When I looked inside of these I could tell I had no hope of making them work again. Then a found this great channel and know if anyone could fix them it was this crew. Thanks for the great channel!

[@Evergreen64]

I've always been so impressed with the creativity of the engineers at HP. They really worked with what they had to do some amazing things.

[@CuriousMarc]

They were genius analog circuit designers.

[@jamesnorman415]

This episode reminds me of my student days when I was the student lab assistant. I learned more about electronics while repairing the test equipment that my fellow classmates destroyed than listening to the lectures. 😊

[@kaunomedis7926]

I don't see a problem rewinding transformer. Learn this art in childhood.

[@vmiguel1988]

I am disappointed without transformer rewinding!

[@simontay4851]

There is no way even curious marc could repair such a specialised transformer. The secondary has lots of taps and is on top of the primary. To get to the primary, he would have to unwind the secondary and he doesn't know how many turns the primary has. Its fxkd.

[@lyrebirdcyclesmarkkelly9874]

Actually not that hard, Tx has only three secondaries, called out on the schematic. I used to design and build specialist drives for turntables and routinely got custom transformers wound to my specs for surprisingly little money (often

[@Andy_T79]

​@@simontay4851We can put men on the moon, ISS 25 years in orbit, space telescopes, satellites, auto landing and reuseable launch vehicles, probes, rovers, and helicopters on Mars, .... but 'No way' could we rewind a 60s transformer! Yes you're right that kind of alien tech is lost to the sands of time along with pyramid construction techniques! 🤦‍♂️🤣🤣

[@jasonmurawski5877]

@@simontay4851sure he could. It’s 3 outputs on the secondary, probably 3 separate windings, too. The schematics may tell you the number of turns, but if it doesn’t then you can easily calculate it since you know the voltages

[@philmayf]

I know it's a crazy longshot, but it feels like there should be someone out there that understands winding custom transformers

[@SeanBZA]

Easy to do, there are plenty of rewinders who will take that one apart, mark all the windings for turns, diameter and such, and then reuse the core, with a new paper former, to rewind the transformer. Easy enough, just that often it is cheaper to buy a new transformer, but for old ones that are not there rewind is the only option. Just look for local motor rewinders, and give then the transformer to do, and it will come back in a few days looking all new and smelling of fresh varnish. Plus also will have improved winding wire, capable of much higher temperature operation, and better insulation that is not paper based.

[@keithmarlow]

@@SeanBZA Exactly, they can rebuild it...

[@SeanBZA]

@@keithmarlow Yes, had a small 100W motor rewound, because there was no stock available, all 6 moths out, and as it was an extended shaft version, of a common regular split phase motor, rewinder it was, with new wire, and a few drops of oil into the bushing felts to keep them happy. Took around 4 days total, and it came to more than the price of a new motor that size, but again, no stock, and 6 month lead time from Italy for it.

[@ifitsrusteditsmine]

Marc, a guy that enjoys both playing with pure junk and Apollo modules.

[@simontay4851]

The previous man's junk is curious marc's treasure.

[@c1ph3rpunk]

I’m mesmerized by how that oscillator works, and how apparently stable it is considering it’s basically just a couple light bulbs. It would not surprise me if it’s as stable as, perhaps more, than a 555 timer. Just because something seems primitive, doesn’t mean it is.

[@SeanBZA]

Neons are selected Ne2A, selected for having the same breakdown voltage, and then put into pairs.

[@Agnemons]

Good to see Marc socking it to the dirt.

[@DrFrank-xj9bc]

Marc, thank you very much. Very nice, that you restored this old VTVM.. I've done that @ Airforce lab 1980-1982. I've repaired and calibrated many of those and similar instruments with different optical choppers. hp also used synchronous motors with hole disks, which interrupted the light beam of small incandescent light bulbs. At eevblog, we have replaced those neons in FLUKE 845AR/AB instruments. Those neons need to fire in the dark, so at that time, radioactive substances inside the bulbs were added. One of those neons is the AC3/NE-2U, which fires at

[@CuriousMarc]

You would be right. Neons in photochoppers need to fire in the dark, so they always have a trace of radio active element added to the gas (that's what the little dot in the neon means in the schematic). We'll replace it with the correct bulb in the next episode.

[@MLX1401]

"But this one's special" Spoken like a true collector 😁

[@TheDefpom]

I designed a replacement PCB for the 3400A to replace the chopper board, it’s up on PCBway.

[@Edisson.]

Hi, I saw the video, great work, my 3400A is not working yet - it was damaged a lot and that's probably why it looks like new (probably it was broken for a long time in some warehouse) the input amplifier with Nuvistor was fried. Similar work with the design was done by Mr. Carlson, did a huge amount of research on neon lights and ended up redesigning the entire circuit and replacing the neons with red LEDs. Nice day 🙂 Tom

[@gvii]

That was really interesting. I have a huge soft spot for these old bits of equipment, so it warms the heart to see at least one of the two brought back to life. Thanks for sharing this, it was a lot of fun to watch.

[@keithmarlow]

whoever was trying to restore the units before clearly didn't know what they were doing, or didn't have the right equipment to properly fault find. Golden rule, if you don't have the experience or equipment, leave well alone.

[@fritzkinderhoffen2369]

VTVMs are special equipment that always could do things that regular VMs couldn't. This is high end and you undoing the damage done to them a joy. Hope you get plenty of use out of the one that you resuscitated. Look forward to the follow-up video!

[@Hans-gb4mv]

That's no spoiler at the end, but something everyone following this channel should know ;)

[@JeffreyLWhitledge]

I love the way this video includes a native French-speaker imitating Tom Kenny’s fake French accent. Awesome!

[@danielatbasementtech]

Thanks for sticking with this repair … always something for us to learn.

[@chriholt]

Oh man, I haven't used a VTVM since high school, when we built and used Heathkit (!) VTVMs in Electronics shop. Great memories!

[@BlazeGelos]

Wow, I'm from Mexico and bought one of those some years ago at a flea market. I didn't knew how to repair it, but now it looks to me like it could have a problem with the photochopper too, I thought that the neon bulb assembly was actually some kind of a rare vacuum tube lol. I like a lot the way old electronics stuff looked and how they operate so i'll try again, maybe I can finally bring it back to life too. Thanks for the video.

[@Derpy1969]

This is awesome. I did not know such tech existed for volt meters. HP made everything!

[@Gymnos2]

Seems like a cool project! Can't wait for the update.

[@I967]

Excellent work, Marc, thank you for another HP episode. I'll be looking forward to the second part. Pity about the burnt transformer. I'd look into having it rewound because here in Europe these are rare, which is probably not the case in the U.S.

[@tony359]

amazing as usual!

[@coldfinger459sub0]

👍👍 that was a lot of work . To bring back a excellent old HP I learned something today about choppers that I don’t remember learning electronics class .

[@bw6378]

Awesome work as usual. Thanks for sharing.

[@KC9IEQ]

Encore! Encore! REALLY pleased that you have shown so much about optical choppers, I'm currently fighting a noisy Fluke differential voltmeter and suspect a chopper issue there as well. The "black magic" behind tuning these circuits is tribal knowledge, nearly lost to time.

[@gerryjamesedwards1227]

This should be a useful addition to the lab. There are quite a few instruments of a certain age that call for a VTVM in their service manual calibration/alignment procedures.

[@DavidSmith-zx7wz]

Love the old repairs, thanks Mark!!

[@kirknelson156]

its really cool to see you restoring test equipment I used to calibrate when I was in navy.

[@kaviter77]

I envy you. You live in long lasting democratic country that had all this cool devices. I'm from Poland. Thru communist time we fall so much behind western countries in technology, and of course all this nice western devices were not available here. I got my hands on fancy polish multimeter from 70's, that was aimed only for state professional market back in a day, and most likely costed fortune in communist reality. I managed to restore and fix all electronics using original old parts (except electrolytic caps), I only miss now nixie tubes that someone took from my meter for some stupid clock. Hope to soon find some in reasonable price (build some LED replacement for purpose of renovation) and put it back together. I'm really surprised how good it actually is. Best regards Marc, you are by far my favorite KZbin channel.

[@Readbooks6800]

I don't understand most things in your videos, but it makes me curious about electronics especially one which are old. I am learning things and would love to restore them in future. looking forward to the next video.😊

[@AmiPurple]

Yay! Marc and his team at the HP hospital doing miracles

[@HainjeDAF]

What a creative use of socks! 😂

[@mikefinn2101]

Nice saving these classic meters well worth the effort Marc you are lucky

[@chrisdooley1184]

Why am I not surprised you have a 1963 original catalog listing that meter 😂! I love this channel despite not having very much electronics background but I do learn something every video I watch so merci bcp Marc! Ce canal est mon préféré ❤️

[@DavePKW]

Another great troubleshooting video. I definitely learned something in this one. Thanks.

[@624Dudley]

Love the DIY SpongeBob gag! 😄 Oh, and the whole rest of the episode too. 👍

[@flomojo2u]

Another really enjoyable video troubleshooting to a fixed unit, so satisfying! It's so cool seeing inside this old gear, and having the schematic really makes for a delightful time, getting it working.

[@nicolasgoldberg3114]

Hi Marc, great job on restoring the vtvm and thank you for sharing ☺️

[@miroslavstevic2036]

This channel is fantastic.

[@OmarMekkawy]

Maybe it's time to learn how to rewind transformers ? 😂

[@guyh3403]

in-cre-di-ble ! Thank you so much for these video's.

[@Runco990]

I managed to score a newer (brown case) version of the 410C for well under the usual $10,000 asking prices on the auction site. It is near MINT!!! It has become my pride and joy for doing RF alignments. Nothing beats a moving needle for this. 😊 BTW, there ARE solid state replacements for the Photo Chopper for it and the 3400.

[@radio-ged4626]

I love how they worked around resolving the chopper circuit design to null the input noise. So simple it's beautiful. Great video.

[@websterleone]

I'm amazed you didn't replace the blown winding in the transformer with how far you go on some of these xD

[@genetomblin2883]

I have not seen one of those giant AC probes in a very long time. Well I am an old man, so these things are to be expected as long as my memory holds up.

[@scowell]

I was expecting to see a battery... the VTVM's I've opened have all had a leaking dry cell in them for ohms, requiring some battery holder cleaning. Lovely to see it come up and calibrate so nicely, thanks for saving them for future people to enjoy.

[@joes5669]

Your videos keep my attention until it's too late to give them a thumbs up. But they're so excellent that I go back to hit that thumbs up even if it means having to watch another commercial to get it done! Thanks!

[@nathanraymond3899]

Hi Marc, I’m just finishing a MS EE degree at UVM, these videos are great, I love watching an experienced engineer ply there craft, and solve these problems, thanks and keep up the good work

[@cheesetomatoes]

I love the custom Spongebob announcements

[@briangoldberg4439]

coool. I always wanted one of those things for making adjustments on old TVs, but I don't have enough bench space lol

[@Snowsea-gs4wu]

I have just fixed a smart light, changed the capacitor and feel like a genius! OMG the work you do guys, congrats!

[@twingoman2000]

Love your Work! It is so crazy to watch your skills, knowledge and understanding. Me personaly is also working on broken things but farcaway from your skills and knowledge. Good thing in your videos, most of your explanations are to understand and leads me to try to get better understanding of what might be the failure. I really love your Chanel!

[@philmonat9352]

Wow ! We've come along way.

[@memeswithoutcontext4716]

Nice video!

[@DerekHerbst747]

I wish someone would donate a HP VTVM to me, especially in a sad state. I love restoring old equipment!

[@antronargaiv3283]

I have one of these (don't remember where I got it...a gift at some point, and the property tags have been removed) which you have inspired me to debug and get working. I suspect the chopper, but now that I have seen how easy it is to get at the neons, I think there's hope for mine. Thanks for this episode!

[@Edisson.]

Attention, the original neon lamps cannot be easily replaced, it is a selected pair, the new ones produced today have a different design and cannot be used in a photo chopper, watch the video Mr. Carlson about the Null Voltmeter HP Nice day and successful repair 🙂 Tom

[@antronargaiv3283]

@@Edisson. Marc promises a source for the original neons in the next episode...talk about a cliff hanger! Also, @CuriousMarc -- what is the coax you used to replace the old test leads (looks like RG-174)?

[@cheapasstech]

You can rewind the transformer… should be easy to calculate the windings secondary looks good so just count em

[@jasonmurawski5877]

Especially when they have a good unit. I’d love to see a transformer rewinding video

[@Edisson.]

@@jasonmurawski5877 You don't need a good unit for that, you have a defective transformer - such a transformer can be replicated by unwinding and counting the turns, or you can measure the diameter of the wire with a micrometer and recalculate the transformer - you have the necessary voltages in the diagram, the dimensions of the sheets are given, and the saturation of the material can also be calculated. Most importantly, don't forget to put spacers from transformer paper or tape in the primary winding after every 50V, and the transformer will be better than the original, because today's varnishes have much better properties. 🤔 but the amount of work to do it manually without a winder 😵‍💫 ........... 😂 Nice day 🙂 Tom

[@jasonmurawski5877]

@@Edisson. having a good unit means you can calculate the number of turns instead of counting them. Of course, there’s nothing wrong with counting the turns. You could always calculate it if you knew the voltages used but you don’t always know that.

[@Edisson.]

@@jasonmurawski5877 You probably misread what I wrote (or I wrote it incomprehensible, I don't speak English very well), they have documentation where the voltages are listed, I listed unwinding the threads only as an option. Edit: Maybe you were watching the wrong way, during the video the documentation is not only mentioned, but also shown

[@wacholder5690]

Moooh ... I once had an HP 410B ... and sold it. The -C is also nice. But I have an assortment of Nixie DVMs at hand. Thanks for sharing !

[@Renville80]

I enjoy this channel and the way you dive into technology of decades past. May I make a suggestion for your elevator music sections? When you show the slides, can you have the title on top of the screen instead of the bottom? The reason I ask is that since I can't hear, I use the closed captions, and so some information gets hidden behind the captions. Just a tiny quibble, but otherwise I love the content and method of presentation on these videos! 👍

[@martinsiebert1368]

I have three Rohde & Schwarz URI tube voltmeters in use alongside a modern desktop multimeter. This is supplemented by a digital handheld multimeter and four passive handheld multimeters. I use the handheld multimeter most often, followed by the three URIs. The URIs are ingenious in terms of design: DC voltage, DC current, resistance, AC voltage and AC current can be connected simultaneously and the measuring mechanism is connected according to what you want to measure. This principle helps to avoid errors during measurements. The URIs are supplemented by high-voltage probes, divider probes and HF probes. The desktop multimeter is only used for complex series of measurements or if there are any special requirements when measuring voltages or currents in experiments.

[@glitchwrks]

Nice to see one with an intact scale! I've got a number of HP analog meters in this case style that have *very* peely scales, including a few mirrored scale units :/

[@filmclipuk]

Brilliant Saturday breakfast restoration! I like the way its dead brother is flat on its back at 28:54 😂

[@SubTroppo]

Perhaps stickers which state "C'est Foutu!" designed be applied to faulty, kept for spares, equipment be made available in the merch store.

[@tomschmidt381]

I picked on up at a hamfest years ago but could never get it fully functioning so it went back to another hamfest. There are upgrade kits on eBay but are pretty expensive.

[@richardhole8429]

I really want to see that transformer rewound. You can do it!

[@ray-kast]

hahah is that a custom spongebob titlecard?

[@dodaexploda]

A heads up for the old plastics and rubber that are hard, you can bring them back somewhat. They get hard because they release their oils and dry out. If you dunk them in somehting like wd-40 or motor oil for a day, they will reasorb some and become pliable again.

[@garbleduser]

For an elderly neon in a photo-chopper, slapping a radioactive tickler next to it can be an effective stop-gap.

[@gtoger]

I always try and fix my ohm problems before moving on to others.

[@absurdengineering]

The “capacitor crusties” are a disease I’ve seen in some early 60s power supplies. It looked exactly like what you got. It affects the yellow-ish transparent-clad electrolytics with white-ish rubber seals. Some of the capacitors still measure OK in early stages of the disease.

[@douro20]

I didn't know the 410C was a VTVM- I always thought it was a FET unit. I thought about building a probe for my old Sylvania VTVM- it needs a special tube with a 125mV filament which is almost impossible to find- but I intend to modify it so I can use a small acorn diode.

[@CuriousMarc]

@douro20 Like the 400E and the 3400, I think there are two versions of these, the early ones with tubes and the later serial numbers with FETs. Good luck with your AC probe!

[@EricLikness]

This wasn't a self-inflicted "owie" like the poor HP9825 and it's lack of a crowbar circuit suffered (no TTL were hurt on these meters), but man, somebody truly tortured both these meters before tossing them away. But they both find the right home that's for sure and will receive the attention needed to show off their many talents. Glad Eric S. was there to get the initial de-grunge-ifying.

[@EricLikness]

And I am sooooo happy to hear they still make the right neon tubes to replace the ones in the original meters. That is amazing.

[@neilshep50]

That transformer was cooked like my wife likes her steak...............................burnt to a crisp 🤣 Recently seen the same colour on one of the sets of windings on a 3-speed induction motor from an air filtration unit. Someone never cleaned the filters so.......

[@erickvond6825]

While expensive and time consuming it is possible to have a transformer rewound. Hence the second VTM could be put back into service. It's been awhile since I last used a service like that so I'm unsure where to send you for quality services of that nature. You might try looking into companies that rewind electric motors.

[@ntsecrets]

You’re not going to try to rewind the transformer?

[@av8bvma513]

Analog meters are very satisfying. I feel absolutely Nothing for digital, no matter what name or however much it may cost. You may prize(sic) my AvoMeter 8 MkIV from my Cold, Dead Hands!

[@MarcelHuguenin]

CuriousMarc never stops to amaze me. His level of knowledge and skills are unbelievable. What a joy to watch and learn something in the meantime.

[@Powertampa]

I was half expecting a "how to wind your own transformer" interjection by someone who you know has way too much time on their hands. :)

[@marekkowalski6767]

tnx 🇵🇱 ( Poland).

[@sloth0jr]

I would actually be really interested if you had any way of rewinding the trashed transformer.

[@soothcoder]

You could re-wind the transformer (Feedback Loop style) :)

[@user-bp6wk4qe9z]

2:24 I thought it was Grady from practical engineering

[@SLeslie]

People can be fascinatingly unsmart. I have heard multiple sorties when individuals tried to measure with a 10 or 20 amps capacity DMM how much current a car starting battery provide by basically shoring the battery with the DMM.

[@therealjammit]

The blown transformer doesn't look too difficult to re-wind. At worst you have a working one to reference, even teardown the working one to get wire gauges.

[@68hoffman]

kool

[@JulieanGalak]

Couple of years someone gave me an old, non-functional, Simpson vacuum tube VOM. This is really making me want to restore it.... But I've literally never dealt with tubes... I suppose the first thing to do is get a Variac, to power it on gently and see what's up...