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.

i appreciate you utilizing your accent for the spongebob joke

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

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!

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.

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.

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!

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.

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.

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?"

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. 😊

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

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

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

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

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

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

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.

Good to see Marc socking it to the dirt.

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

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.

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

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

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!

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.

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

👍👍 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 .

I am disappointed without transformer rewinding!

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.

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

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

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.

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

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

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

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

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.😊

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 ❤️

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

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.

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.

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.

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

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

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.

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

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!

Love the old repairs, thanks Mark!!

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

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.

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.

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 KZfaq channel.

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

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

Awesome work as usual. Thanks for sharing.

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! 👍

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

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

What a creative use of socks! 😂

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!

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

amazing as usual!

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

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

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

This channel is fantastic.

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 :/

I love the custom Spongebob announcements

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

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.

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

Wow ! We've come along way.

Nice video!

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.

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 !

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

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!

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

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

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

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.

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.

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

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.

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.

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.

I appreciate the explanation of the photo-chopper! But how does it not destroy the input impedance? At 60 Hz the LDRs wouldn't have time to reach high resistance, I thought 🤔

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.

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. :)

hahah is that a custom spongebob titlecard?

Hi Marc i have a question. Did you manually set this video to "Premium 1080P Enhanced Bitrate" or did youtube did this themselves? Its a bit annoying since they usually downgrade the normal 1080p to the point that it looks worse than 720p when the Camera is moving. I am happy to pay Premium to see your content in blur-free HD but maybe it was just a mistake :) EDIT: But this could also just be a Camera issue sometimes in this videos since it sometimes looks actually good

Is there a modern replacement coaxial cable that someone could recommend? My cables are cracked and brittle alone the whole length and need replacing. Something flexible but also the same diameter would be great.

tnx 🇵🇱 ( Poland).

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...

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!

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

kool

Hi Marc: can you please let me know where you were able to find the replacement test lead cables and strain reliefs? Thanks!

Great stuff! A bit sad that I only discover this 9 years after it was made... What happened to the defunct brother? Did you ever find anyone capable of repairing the blown transformer? It's not hard but it will cost mucho dinero...

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