I've had a tough week for a variety of reasons, and I really need to keep my mind focused on pleasant, soothing things. So it's been fabulous to have THREE new CuriousMarc episodes within the past five days! THANK YOU!
This channel has come far indeed. 14 years ago, Marc was building an R2-D2 replica, now this labs sports a full set of NASA Apollo HF equipment, a full set of vintage HP lab equipment and, apparently, some of the finest and most precise clocks 1960's money can buy.
HP was an amazing company. We have countless conveniences available today that were developed using their amazing equipment. I really appreciate your teaching and troubleshooting style as I learn so much about electronics. During my career (aviation) we used countless HP and Techtronix equipment for testing and development.
The HP 105x had very-low phase noise. Lower even than Cesium or Rubidium clocks that came into labs. Back in the days of WWV and stick-in-sunlight clocks, the local HP 105 or 106 was the Standard for check-adjust of freq-time counters that had pretty nice selected quartz in oven internal oscillators (mostly HP). Cross fingers for passing cal, because adjustment takes days as you make them unstable by adjusting and have to wait. Good thing we were paid by the month.
Amazing how this logic was implemented with discrete components. Just pure joy to see how all the backups and switching are made with transistors and Zieners. It takes a lot of experience and knowledge to come up with such elegant solutions. You ain't gonna get such education nowadays as it would (and is) implemented in software instead. But the skill to implement it in hardware also would be valuable to have.
Excellent repair, as always Marc! I have an old CDMA 3G cell phone tower rubidium module and one of those dutchtronix oscilloscope clock kits from several years ago. But I have always dreamed of having a cecium clock like yours! Awesome content sir!
Lead-calcium telco cells can last for a few decades of standby use. The only problem is that they won't fit inside the enclosure. I didn't know they made "low-voltage neon" indicators. Tec-Lite did make LED versions under the same product series.
I have the proper Raychem infrared tool (IR-550) for those solder-shrink connectors. I bought it when you could get them for a song as surplus. The last time I saw a new one for sale from TE it was over US$10,000! And they charge $400 for a lamp which costs less than $20!
@@CuriousMarc I've seen many sold with an attachment for the hot air gun that lets you heat the back side at the same time. I think for when space is limited mostly so you don't blast what's behind it and you don't cook one side while the back side is still cool when you can't move around the wire.
+1 for the CDC 3600 cameo. We had one of those (and a 3800) at UMass/Amherst while I was there. Replaced by a CYBER 74 one summer. On which I took my assembly language programming course. Unsurprisingly, I never again used the COMPASS assembler. REAL computers have switches and lights, and the 3600/3800 had oodles of both.
An interesting comparison can be made with a centre zero moving coil meter. You put your two frequencies to compare on each side of the coil and common the grounds. You can see slow phase drifts really nicely. I've done that to compare the short term instabilities of a GPS source and a OCXO. The bigger the meter movement, the better.
Now that thing has proper battery backup, maybe Marc could do a co-op with Scott Manley and take the clock for a ride on his (small) plane. You know, to properly re-create those 1960's clock syncing experiments. I was thinking of maybe flying it to Houston and sync with the official NASA (or Space Force) clock. That way, Marcs Apollo exhibit could run perfectly in sync with the rest of NASA.
Now that is an oscillator, I have a HP105B, but only a Trimble GPSDO as a reference, unfortunately not stable enough, as I can easily see the GPS bobbling about, nothing like your Caesium reference. The best solution I've dreamt up is to make a box that monitors the drift over a long term and use that to set the 105. That concept is still in the thought process, but the design is starting to form in my head.
Fantastic series. I was able to follow along super duper bien. Amazing what analog circuitry is capable of, coupled with the repairs using the scope, meters and simple tools. This is what I needed following an intense week of election coverage. Thank you so much. 😎What is the current draw for the stack?
Current draw is 500 mA for the HP 106B (these darn ovens!), and 170 mA for the clock, so about 670 mA. Probably lasts 5 hours on the battery. The internal battery was just for intermittent power faults. For longer term battery backup you needed to add the larger external battery supply. That's the box you can see at the bottom of the flying clock rack.
I’m 16 and I religiously watch this kinda of content, I have back pain that requires my to use a Cain, and I’m a ham radio operator. Where’s my pension?
I bet you could cut that LVN open on the lathe, replace the neon bulb, and then use some shrink tubing to put it back together. Or at least you could test the neon by itself, to see if the neon is bad or if it's one of the other components in the LVN.
Wow, 7 transistors to not overdrive the circuit. That's some serious investment for the 1960's! Shows you just how important it is for stability to drive the crystal at low power.
Ha! "Oui" yogurt container recycling! Great for small screws you don't want to lose, small tools you want to keep handy, solvents (silicone snap-on lids now available on Amazon, and many other uses,
I wouldn't say that charging lithium uses "same scheme" as NiCd. Lithium is easily charged with CC/CV and it will stop drawing current when it's done, while NiCd will gobble up excess energy forever converting it to heat (and so you need to either do that with low enough current, or have ∆T or ∆V stop condition). I was confused by statement that you can "trickle-charge" lithum batteries, because that term is often used to mean charging continuously with low current (which absolutely shouldn't be done to lithium). But you actually meant constant-voltage charge, so that is fine.
This is incorrect. These are LiFePO4, not Li Ion or Li Poly. They charge completely differently, which is why you can just swap them for lead-acid without having to replace the charger, and keep them at constant voltage charge at the end.
@@CuriousMarc What is incorrect exactly? Charging behaviour is similiar for all lithium types. You can keep li-ion at constant voltage too and they won't overcharge (it's just not practical for long term because li-ion loses capacity quickly when fully charged). And bad things will happen for all lithiums if you "trickle-charge" them, which is usually used to mean charging with small current all the time. As for swapping you always need to considier logic of given charging circuit, it won't be compatible in all cases.
Charging behavior is different for different Li types, as is chemistry. Otherwise what you say in this second post is not incorrect. I believe LiFePO4 is the only type you can safely charge in an unmodified lead-acid charger, or a NiCd charger with adjusted voltage as I do here. For Li Ion and Li Poly, charging them optimally is more complicated and you need a hard stop at the end not only for the reason you mention, but primarily for safety, preferably enforced by protection electronics in the battery.
Hey Marc! Just from the feeling, the ovens are a little bit too nervous in regulation. I could be wrong, but I expected the inner oven to be less nervous than the outer one. If there is a unsteady draft in the room, I would expect the outer oven to compensate first and then the inner over to react on the outer oven's reaction. The battery mod is cool but the manufacturer of your 24V LiFePo4 seems not to have that anymore. Have you checked the datasheet? Coud very well be that your battery may be charged continuously, as it has an internal BMS that cancels charging automatically. And for a LiFepo4 these 250mA charging could just be called "trickle charging" as it can be charged by 1C / 6A. But just continue what you do, a week without one of your videos is a sad week!
I'm not sure about the oven, whether it's normal or not. Now it's become perfectly stable. It's not a supply problem, or at least not the one I repaired, plus it gets re-regulated before it goes to the oven controller as I explain in the video. As the oven regulation is stable and the oscillator is behaving as it should, I have not explored it further.
@@CuriousMarc I wasn't 100% sure about it, it just felt suspicious. It also wasn't clear, how far in the heating process the unit was when you shot the video, and we saw the dancing needle. But if the temperatures are now set and the frequency is stable, it was just the two ovens racing against each other for the target temperature. Thanks for coming back to me and clarifying things. Waiting for the next unit to appear on your channel!
@@uki352 I'm totally with you. It does feel suspicious. And it's never good when things "repair themselves". It usually means you are not understanding something fully, and might bite you in the behind down the road. However in this case it's been running fine for 4 month now, and tinkering with it would involve opening the dual oven, which might be asking for trouble. Would make for a good video though!
@@CuriousMarc If I recall correctly, Symmetricom Double Oven OCXOs in GPSDOs use an outer oven to create a fixed temperature barrier and an inner one to add that exact right amount of heat to get the quarz to the right size. I have seen circuits where the power supply for the ovens was limited as that expands the lifetime of the heaters when starting cold. And I can imagine that HP did exactly that. With current limiting the two ovens would race against each other. If the OCXO tube has separate supplies for the ovens, you could check that by using separate bench PSUs and watch the needle go straight. I do have two ovens in a smaller form factor that served the German Military Intelligence Services including splitter, dividers and filters for 10MHz, 5MHz and 1MHz outputs. If you or your team is on a visit to Germany one day, you can have one ;) But I can check shipping costs if interested.
Hi Marc, wouldn't a Rubidium oscillator be as close to the Cesium clock as practical? Or is it more about using period HP gear? I have several Rubidium Oscillators including a very nice 15MHz oscillator from Lucent. Cheers!
The Cesium is still unbeatable. The Rubidium would beat the super-quartz by an order of magnitude, but just like the quartz, it continuously ages. The Cesium is another one or two orders of magnitude better, and most importantly, it has no aging drift. That's why you still need to discipline the Rubidiums with a master Cesium - usually the one that flies over your head in the GPS system. And that's why the HP Cesium tubes (now Microsemi) are still made and in high demand today.
This was such a fantastic restoration Marc, I enjoyed it a lot. You keep surprising me every time and I keep thinking that you must have bought all of HP's vintage parts 🤣 Thanks for this great video!
9:50 I never knew this. What happens to quartz crystals when they age? Is there some sort of atomic entrainment that causes its resonant frequency to fall over time?
I'd suppose it's some atomic stuff in the crystal itself, but I don't know for sure. I tell you, once you have an atomic clock, it becomes pretty obvious that all the quartz crystal oscillators in your lab keep going down and down and down... Even though the 106B is 10x as good as a normal ovenized quartz oscillator in that regard, I can still see it creeping down, actually more easily seen than in other oscillators because the 106B is so steady and monotonous in its behavior. The effect vs. Cesium is visible within a day.
You'd think they really would want an indication that it's running on battery considering that's gonna run out pretty fast if nobody notices and they went to great lengths making sure it does not turn off.
But an indication that its running on battery would drain the battery faster. LEDs had not been invented yet and a low voltage neon would draw quite a lot of current.
The internal battery is just for short power interruptions - lasts a few hours. There is another, much larger external battery power supply that you need to add to the setup for long term battery backup. You can see it, it's large box at the bottom of the flying clock rack.
@@CuriousMarc Never realized there was another external battery in that rack. I wonder why they didn't run it off the airplane generators. Those WW2/early cold war era planes usually had ample reserve power. (You know, for all those secret toys of war that were uninstalled before handing the aircraft over to civilian users).
I'm curious - at the end, you remove ac power and the 115BR continues to run. Does the 106B supply power to the 115BR? It seems to me the motor in the 115BR (not to mention the analog divider/multiplier circuitry) would use a relatively large amount of power, and I'm wondering what the backup battery life of the combination of those instruments would be?
0:52 Did they successfully sync them though? A later experiment flew an atomic clock to confirm the time dilation predicted by relativity and did indeed show a time difference from a clock that remained stationary at lower altitude, so...
Yes, they did, to their 1 µs goal, which the best the HP 115BR tick could do. Relativistic effects are in the nanosecond range, far below this. The later relativity experiments (the Hafele-Keating experiments) were also made with HP clocks by the way, but with much better clocks and much, much better dividers and much faster planes, that allowed them to reach into the realm of nanosecond precision. The relativistic effects were still very small, barely measurable. But they saw it for the first time!
Marc, You say you don‘t want to run the cesium clock for fear of using it up, but isn‘t that a decay clock anyway and uses up the cesium no matter if turned on or off?
You need to track frequency through a mains off, wait an hour, mains on cycle to see if the phase of Cs and 196B move. Then you spend some days correcting the oscillator until its aging falls back into spec. Initially it may be quite bad. But, it should recover back to low aging quicker than when it was new. Than comes the reach for the gold medal. What does it's Allen Variance look like? (Phase noise.) {^_^}
I was surprised too. I guess they wanted to keep the absolute minimum power consumption, and did not want to waste it on an extra incandescent or neon light indicator (at the time a non-negligible power drain).
They could have used some mechanical stuff that draws no current (an indicator showing a white star, for example, I think remembering they were used at the time). The battery was probably used only when they wanted to move the device around, or during the time some backup system takes over in the laboratory. So no need to indicate anything.
So that atomic clock retained its constant tick even in spite of being flown on a plane? Because of other experiments showing clocks on planes go out of sync with ground based clocks.
It kept its constant tick within its own frame of reference. Yes it would have drifted while moving. However note that the first time they would have synchronised all those clocks you would still have ended up with the clocks closer together than they were before. Later experiments proved the variance with different reference frames. The most famous being another plane related one where two clocks were synchronised and then one was sent around the world on a 747 as fast as they could go. Then the two clocks were compared and found to be out of sync just as much as relativity predicted.
It sure was affected by relativity - well, we all are, even when driving our car. But the effect is so absolutely minuscule, it was far below what this first flying atomic clock could resolve. However, they later tried (and succeeded) to measure it with a much better atomic clock, a far, far better all-electronic divider, and a much faster plane - actually two clocks in two faster planes, going in opposite directions, and the entire way around the earth, to magnify the effect as much as possible and possibly bring it above the noise floor. That was the famous Hafele-Keating experiment, probably the experiment you are referring to. And they were barely able to measure it - but they saw it above the noise! I recall the time difference between the two clocks due to relativity was in the 10's of ns. All that to say that it only starts to matter if you try to synchronize clocks to the nanosecond. In this first experiment with the HP 115BR, discounting the very slow plane, the tick was only precise to 1 µs. So they were not affected by relativistic effects. Two or more orders of magnitude below the noise level of their experimental setup.
Oh, the discolored one? It's not burned, it's a 1% resistor still within 1%. I had that happen in the HP 3300 repair too. Somehow these high-precision HP blue resistors discolor like that, but it's just cosmetic.
The oscillator has a +24V DC output, you can see it marked as "ACCESSORY SUPPLY" in the top corner of Figure 5-15 (11:00). After Marc hints at the clock adjustment procedure (around 31:40), he says that "the 106B came with a battery that could operate both the oscillator and the clock and I really need to get that functionality back." He then goes on to fix the whole battery related stuff, so I'm pretty sure he connected it the way it is supposed to be.
@@federicodidio4891 good spot , also at about 2:10 marc mentions the 'special plug' for interfacing , I presume this does the power as well as whatever else is needed.
Why is the tube in the atomic cock a finite life item? It's not like the cesium is actually consumed, it's just moved around. Is there something that makes it cost prohibitive to add something to cycle the cesium back the other way? Or build it so that it can be "regenerated" (e.g. "hold it in orientation X and heat at point Y to temperature Z for Q hours".) That would seem like a highly desirable property for something that costs tens of thousands of dollars and lasts less than a decade. Even if it would double the cost of the tube, that would pay for itself in lest than 20 years.
Comes out of a tiny focusing hole at one end, splattered all over the tube at the other end. You can't just stuff it back in unfortunately. And you can't just open the tube to atmosphere either, or the Cesium will burn or explode in your face. Apparently, even at $20k, it's cheaper to make a new tube than to refurb an old one. I hear the yield on the tubes is low too, these are hard to make! I'm tempted to open one up and try for myself though, maybe I can get help from my buddy Ben Krasnow.
@@CuriousMarcinteresting. Out of curiosity, I tried to check how much is used (if it's just a drop, I could see even getting it to drain off the far end might be hard) and found an AI generated response referring to "clock that doesn't recirculate the cesium" as using about 1 gram per year. If that's not a hallucinating AI, that says something interesting right there.
Would you rather that technology stood still? Nothing to be afraid of, they live on the cusp of some amazing technology advancements, just as the generation who saw this HP equipment did. The iPhone in the pocket is an amazing example of technology advancements at an astonishing rate, just 40 to 50 years after this HP clock, amazing!
I've had a tough week for a variety of reasons, and I really need to keep my mind focused on pleasant, soothing things. So it's been fabulous to have THREE new CuriousMarc episodes within the past five days! THANK YOU!
I feel this.
Hang in there friend
Right there with you.
Same. It's like cleaning some old oil painting, but much more interesting.
I hear ya buddy. This music and Marc's voice just works to mellow out the week and help me relax.
This channel has come far indeed. 14 years ago, Marc was building an R2-D2 replica, now this labs sports a full set of NASA Apollo HF equipment, a full set of vintage HP lab equipment and, apparently, some of the finest and most precise clocks 1960's money can buy.
Hey, don't poopoo my R2-D2. He is a precision space instrument too.
@@CuriousMarc Never said it wasn't. But learning about the dark arts of pre-IC HF magic is just so much more interesting 🙂
HP was an amazing company. We have countless conveniences available today that were developed using their amazing equipment. I really appreciate your teaching and troubleshooting style as I learn so much about electronics. During my career (aviation) we used countless HP and Techtronix equipment for testing and development.
"So how many HP instruments do you need for happiness?"
"Yes."
n+1
"Just one more, your Honor."
Loving this series so far! High-precision clocks are addictive.
The HP 105x had very-low phase noise. Lower even than Cesium or Rubidium clocks that came into labs. Back in the days of WWV and stick-in-sunlight clocks, the local HP 105 or 106 was the Standard for check-adjust of freq-time counters that had pretty nice selected quartz in oven internal oscillators (mostly HP). Cross fingers for passing cal, because adjustment takes days as you make them unstable by adjusting and have to wait. Good thing we were paid by the month.
This schematic is a masterclass in analog circuit design.
I understand maybe 5 percent of this but it's great. I slowly learn new things every time you post. Thank you
Amazing how this logic was implemented with discrete components. Just pure joy to see how all the backups and switching are made with transistors and Zieners. It takes a lot of experience and knowledge to come up with such elegant solutions. You ain't gonna get such education nowadays as it would (and is) implemented in software instead. But the skill to implement it in hardware also would be valuable to have.
This oscillator is so precise, it hertz!
i like how you tick
Your jaunty intro music is always the harbinger of a good time. Pun fully intended.
Double ovenised, for extra crispy square waves! 🤤
I think it's sine wave output but that's just nitpicking 😊
VERY satisfying - especially the restoration of the oven battery functionality. Great!
Thank you for recording the cleaning.
I am just binge watching the last couple of videos because I couldn't keep up. Must watch all of them!
I love these solo Marc episodes the most for some reason. Just a guy and his machines.
Excellent repair, as always Marc!
I have an old CDMA 3G cell phone tower rubidium module and one of those dutchtronix oscilloscope clock kits from several years ago.
But I have always dreamed of having a cecium clock like yours! Awesome content sir!
there are some fantastically tiny atomic clock modules now, like smaller than a deck of cards. They are almost what some might call affordable too.
You are always the most interesting fellow doing the most interesting things on the internet. And that is really saying something :)!
Another banger of an episode 🔥 all Marc lately I can’t complain
This week keeps getting better and better. 🙌
Love your work!
This is increadably relaxing! Also, thank you for bringing my love for electronics back!
Magnificent work! Truly entertaining too. Well done.
Lead-calcium telco cells can last for a few decades of standby use. The only problem is that they won't fit inside the enclosure.
I didn't know they made "low-voltage neon" indicators. Tec-Lite did make LED versions under the same product series.
Cool.
I can’t help but grin when his theme starts 😊
Wonderful! I was just going to sleep and here is such a wonderful video.
I have the proper Raychem infrared tool (IR-550) for those solder-shrink connectors. I bought it when you could get them for a song as surplus. The last time I saw a new one for sale from TE it was over US$10,000! And they charge $400 for a lamp which costs less than $20!
Oh, that's how you are supposed to do it? I just use my hot gun and watch carefully...
@@CuriousMarc I've seen many sold with an attachment for the hot air gun that lets you heat the back side at the same time. I think for when space is limited mostly so you don't blast what's behind it and you don't cook one side while the back side is still cool when you can't move around the wire.
@@zyeborm Kool. Now I want Douro’s $10k tool though ;-)
Thanks, Marc always learn something new from your videos, your explanations are priceless. .. Please keep making interesting videos.
Hi Marc, be carful with the battery, it could overheat as the packing is a good heat insulator.
Yes, that's to keep it warm and cozy! But at 1/10C discharge and very low internal resistance, heat is not a concern.
Thank you Marc - what a pleasure to see this
Great video !!
Very good video, thank you.
Gorgeous video content, thank you curiousmarc and the team
+1 for the CDC 3600 cameo. We had one of those (and a 3800) at UMass/Amherst while I was there. Replaced by a CYBER 74 one summer. On which I took my assembly language programming course. Unsurprisingly, I never again used the COMPASS assembler. REAL computers have switches and lights, and the 3600/3800 had oodles of both.
I'm here for the aesthetic of the TEC catalog lol. Great video as always, thank you Marc.
I want that as a bedside clock!
An interesting comparison can be made with a centre zero moving coil meter. You put your two frequencies to compare on each side of the coil and common the grounds. You can see slow phase drifts really nicely. I've done that to compare the short term instabilities of a GPS source and a OCXO.
The bigger the meter movement, the better.
Very cool as usual. One comment tho: I would ALWAYS fuse a LiFePo4 battery.
Anyone else enjoy his adorable pronunciation of “Oven”⁉️
Well, it is spelt 'oven', not 'uh-ven', so it's understandable.
LiFePo4 for the win! Excellent upgraydd.
Now that thing has proper battery backup, maybe Marc could do a co-op with Scott Manley and take the clock for a ride on his (small) plane. You know, to properly re-create those 1960's clock syncing experiments. I was thinking of maybe flying it to Houston and sync with the official NASA (or Space Force) clock. That way, Marcs Apollo exhibit could run perfectly in sync with the rest of NASA.
@@ReneSchickbauerI doubt the plane will carry the weight of this 60's stuff... 😂
@@feicodeboer I think the full rack weighs less than a person.
Now that is an oscillator, I have a HP105B, but only a Trimble GPSDO as a reference, unfortunately not stable enough, as I can easily see the GPS bobbling about, nothing like your Caesium reference.
The best solution I've dreamt up is to make a box that monitors the drift over a long term and use that to set the 105. That concept is still in the thought process, but the design is starting to form in my head.
No puny PPM or PPB, it's parts in 10^11!
Marco Reps @reps wants a slice of that I guess 😀
That would be 10 ppt... That's just insane accuracy! I'd love to see jitter of those things.
Fantastic series. I was able to follow along super duper bien. Amazing what analog circuitry is capable of, coupled with the repairs using the scope, meters and simple tools.
This is what I needed following an intense week of election coverage. Thank you so much. 😎What is the current draw for the stack?
Current draw is 500 mA for the HP 106B (these darn ovens!), and 170 mA for the clock, so about 670 mA. Probably lasts 5 hours on the battery. The internal battery was just for intermittent power faults. For longer term battery backup you needed to add the larger external battery supply. That's the box you can see at the bottom of the flying clock rack.
@@CuriousMarc ...correction: oeven😃
Oui
Maybe you should invest in a gantry crane across the ceiling to help lift these old boat anchors.
I’m 16 and I religiously watch this kinda of content, I have back pain that requires my to use a Cain, and I’m a ham radio operator. Where’s my pension?
I bet you could cut that LVN open on the lathe, replace the neon bulb, and then use some shrink tubing to put it back together. Or at least you could test the neon by itself, to see if the neon is bad or if it's one of the other components in the LVN.
I'm pretty sure it’s the neon. I was thinking the same, open it cleanly on the lathe.
I initially read the title as "Double Oversized Quartz Oscillator", which, given the enormous can inside, kind of works too. :-)
Simply amazing
Wow, 7 transistors to not overdrive the circuit. That's some serious investment for the 1960's!
Shows you just how important it is for stability to drive the crystal at low power.
Careful insulating a rechargeable battery like that; depending on charging efficiency it could subject it to thermal stress.
would love to see "marco reps" meet marc once :)
Continuous charge is fine for NiMH as long as you keep it below 0.1C or so.
Can it take two power outages without you resetting in between? Thanks for sharing these nice resto videos, lot's to learn.
Yes. The light just tells you that you lost power at least once. Resetting is just an acknowledgement by the user that he read the indication.
@@CuriousMarc Thank you very much for the answer, i thought so myself just wasn't sure.
Ha! "Oui" yogurt container recycling! Great for small screws you don't want to lose, small tools you want to keep handy, solvents (silicone snap-on lids now available on Amazon, and many other uses,
I would love to have that oscillator and clock. So cool.
I do wonder, could the original packing serve as an insulator around the battery, leading to too high battery temperatures?
Very nice job ! Did the maple syrup helped ?
I wouldn't say that charging lithium uses "same scheme" as NiCd. Lithium is easily charged with CC/CV and it will stop drawing current when it's done, while NiCd will gobble up excess energy forever converting it to heat (and so you need to either do that with low enough current, or have ∆T or ∆V stop condition). I was confused by statement that you can "trickle-charge" lithum batteries, because that term is often used to mean charging continuously with low current (which absolutely shouldn't be done to lithium). But you actually meant constant-voltage charge, so that is fine.
This is incorrect. These are LiFePO4, not Li Ion or Li Poly. They charge completely differently, which is why you can just swap them for lead-acid without having to replace the charger, and keep them at constant voltage charge at the end.
@@CuriousMarc What is incorrect exactly? Charging behaviour is similiar for all lithium types. You can keep li-ion at constant voltage too and they won't overcharge (it's just not practical for long term because li-ion loses capacity quickly when fully charged). And bad things will happen for all lithiums if you "trickle-charge" them, which is usually used to mean charging with small current all the time. As for swapping you always need to considier logic of given charging circuit, it won't be compatible in all cases.
Charging behavior is different for different Li types, as is chemistry. Otherwise what you say in this second post is not incorrect. I believe LiFePO4 is the only type you can safely charge in an unmodified lead-acid charger, or a NiCd charger with adjusted voltage as I do here. For Li Ion and Li Poly, charging them optimally is more complicated and you need a hard stop at the end not only for the reason you mention, but primarily for safety, preferably enforced by protection electronics in the battery.
Exactly at 16:47, the power "AC interruption" alarm light blinks, even before you started measurements...
Yes, I noticed that too.
Hey Marc! Just from the feeling, the ovens are a little bit too nervous in regulation. I could be wrong, but I expected the inner oven to be less nervous than the outer one. If there is a unsteady draft in the room, I would expect the outer oven to compensate first and then the inner over to react on the outer oven's reaction. The battery mod is cool but the manufacturer of your 24V LiFePo4 seems not to have that anymore. Have you checked the datasheet? Coud very well be that your battery may be charged continuously, as it has an internal BMS that cancels charging automatically. And for a LiFepo4 these 250mA charging could just be called "trickle charging" as it can be charged by 1C / 6A.
But just continue what you do, a week without one of your videos is a sad week!
I'm not sure about the oven, whether it's normal or not. Now it's become perfectly stable. It's not a supply problem, or at least not the one I repaired, plus it gets re-regulated before it goes to the oven controller as I explain in the video. As the oven regulation is stable and the oscillator is behaving as it should, I have not explored it further.
@@CuriousMarc I wasn't 100% sure about it, it just felt suspicious. It also wasn't clear, how far in the heating process the unit was when you shot the video, and we saw the dancing needle. But if the temperatures are now set and the frequency is stable, it was just the two ovens racing against each other for the target temperature. Thanks for coming back to me and clarifying things. Waiting for the next unit to appear on your channel!
@@uki352 I'm totally with you. It does feel suspicious. And it's never good when things "repair themselves". It usually means you are not understanding something fully, and might bite you in the behind down the road. However in this case it's been running fine for 4 month now, and tinkering with it would involve opening the dual oven, which might be asking for trouble. Would make for a good video though!
@@CuriousMarc If I recall correctly, Symmetricom Double Oven OCXOs in GPSDOs use an outer oven to create a fixed temperature barrier and an inner one to add that exact right amount of heat to get the quarz to the right size. I have seen circuits where the power supply for the ovens was limited as that expands the lifetime of the heaters when starting cold. And I can imagine that HP did exactly that. With current limiting the two ovens would race against each other. If the OCXO tube has separate supplies for the ovens, you could check that by using separate bench PSUs and watch the needle go straight. I do have two ovens in a smaller form factor that served the German Military Intelligence Services including splitter, dividers and filters for 10MHz, 5MHz and 1MHz outputs. If you or your team is on a visit to Germany one day, you can have one ;) But I can check shipping costs if interested.
Now take it with you on a plane for a clock synchronization world tour! 🛫🕐
Hi Marc, wouldn't a Rubidium oscillator be as close to the Cesium clock as practical? Or is it more about using period HP gear? I have several Rubidium Oscillators including a very nice 15MHz oscillator from Lucent. Cheers!
The Cesium is still unbeatable. The Rubidium would beat the super-quartz by an order of magnitude, but just like the quartz, it continuously ages. The Cesium is another one or two orders of magnitude better, and most importantly, it has no aging drift. That's why you still need to discipline the Rubidiums with a master Cesium - usually the one that flies over your head in the GPS system. And that's why the HP Cesium tubes (now Microsemi) are still made and in high demand today.
@@CuriousMarc Ah, thanks for the education. Really appreciate it.
@@CuriousMarc Can we see a Strontium clock in one of those video? They're even more precise than Cesium.
This was such a fantastic restoration Marc, I enjoyed it a lot. You keep surprising me every time and I keep thinking that you must have bought all of HP's vintage parts 🤣 Thanks for this great video!
Awesome !!
@CuriousMarc, Is there any way you can synchronize this fabulous clock with the Udine Solari you have ?
That would be awesome !
9:50 I never knew this. What happens to quartz crystals when they age? Is there some sort of atomic entrainment that causes its resonant frequency to fall over time?
I'd suppose it's some atomic stuff in the crystal itself, but I don't know for sure. I tell you, once you have an atomic clock, it becomes pretty obvious that all the quartz crystal oscillators in your lab keep going down and down and down... Even though the 106B is 10x as good as a normal ovenized quartz oscillator in that regard, I can still see it creeping down, actually more easily seen than in other oscillators because the 106B is so steady and monotonous in its behavior. The effect vs. Cesium is visible within a day.
8:55 "since we are part of a nicely designed instrumentation group [...]" -- where can I sign up for membership in this group?
You'd think they really would want an indication that it's running on battery considering that's gonna run out pretty fast if nobody notices and they went to great lengths making sure it does not turn off.
But an indication that its running on battery would drain the battery faster. LEDs had not been invented yet and a low voltage neon would draw quite a lot of current.
The internal battery is just for short power interruptions - lasts a few hours. There is another, much larger external battery power supply that you need to add to the setup for long term battery backup. You can see it, it's large box at the bottom of the flying clock rack.
So satisfying to watch genius at work while understanding what he is doing. 🙂
@@simontay4851 bistable mechanical flag would do the job. It's not like they were short on money making the thing lol
@@CuriousMarc Never realized there was another external battery in that rack. I wonder why they didn't run it off the airplane generators. Those WW2/early cold war era planes usually had ample reserve power. (You know, for all those secret toys of war that were uninstalled before handing the aircraft over to civilian users).
I'm curious - at the end, you remove ac power and the 115BR continues to run. Does the 106B supply power to the 115BR? It seems to me the motor in the 115BR (not to mention the analog divider/multiplier circuitry) would use a relatively large amount of power, and I'm wondering what the backup battery life of the combination of those instruments would be?
Yes, the 106B supplies the 115BR. The 115BR only consumes only 170 mA, far less than the 106B with the ovens.
Cheap and easy way to synchronize clocks is to get a TinyPFA or a NanoVNA H4 and flash the TInyPFA firmware.
0:52 Did they successfully sync them though? A later experiment flew an atomic clock to confirm the time dilation predicted by relativity and did indeed show a time difference from a clock that remained stationary at lower altitude, so...
Yes, they did, to their 1 µs goal, which the best the HP 115BR tick could do. Relativistic effects are in the nanosecond range, far below this. The later relativity experiments (the Hafele-Keating experiments) were also made with HP clocks by the way, but with much better clocks and much, much better dividers and much faster planes, that allowed them to reach into the realm of nanosecond precision. The relativistic effects were still very small, barely measurable. But they saw it for the first time!
@@CuriousMarc Thanks. I did wonder about the earlier resolution,, etc.
Marc, You say you don‘t want to run the cesium clock for fear of using it up, but isn‘t that a decay clock anyway and uses up the cesium no matter if turned on or off?
I suspect that the cesium is only used up when the oven is on, so I don't think it's used when the device isn't powered.
You need to track frequency through a mains off, wait an hour, mains on cycle to see if the phase of Cs and 196B move. Then you spend some days correcting the oscillator until its aging falls back into spec. Initially it may be quite bad. But, it should recover back to low aging quicker than when it was new.
Than comes the reach for the gold medal. What does it's Allen Variance look like? (Phase noise.)
{^_^}
Be careful, Mark. Precision time instruments are addictive.
Double oven, all the way, what does it mean, wow
Its best to change the battery to its best life voltage for longest life and that is never max voltage.
Is it OK to thermally insulate a battery?
Interesting there’s no indicator for when it’s on the battery, why would that not be something included?
Because it would draw more current from the battery.
Because it would draw more current from the battery.
I was surprised too. I guess they wanted to keep the absolute minimum power consumption, and did not want to waste it on an extra incandescent or neon light indicator (at the time a non-negligible power drain).
They could have used some mechanical stuff that draws no current (an indicator showing a white star, for example, I think remembering they were used at the time). The battery was probably used only when they wanted to move the device around, or during the time some backup system takes over in the laboratory. So no need to indicate anything.
That’s a good point. So I don’t know. I agree it’s odd!
What is realistic time of battery backup ???
nice!
cool!
So that atomic clock retained its constant tick even in spite of being flown on a plane? Because of other experiments showing clocks on planes go out of sync with ground based clocks.
It kept its constant tick within its own frame of reference. Yes it would have drifted while moving. However note that the first time they would have synchronised all those clocks you would still have ended up with the clocks closer together than they were before. Later experiments proved the variance with different reference frames. The most famous being another plane related one where two clocks were synchronised and then one was sent around the world on a 747 as fast as they could go. Then the two clocks were compared and found to be out of sync just as much as relativity predicted.
Almost
It sure was affected by relativity - well, we all are, even when driving our car. But the effect is so absolutely minuscule, it was far below what this first flying atomic clock could resolve. However, they later tried (and succeeded) to measure it with a much better atomic clock, a far, far better all-electronic divider, and a much faster plane - actually two clocks in two faster planes, going in opposite directions, and the entire way around the earth, to magnify the effect as much as possible and possibly bring it above the noise floor. That was the famous Hafele-Keating experiment, probably the experiment you are referring to. And they were barely able to measure it - but they saw it above the noise! I recall the time difference between the two clocks due to relativity was in the 10's of ns. All that to say that it only starts to matter if you try to synchronize clocks to the nanosecond. In this first experiment with the HP 115BR, discounting the very slow plane, the tick was only precise to 1 µs. So they were not affected by relativistic effects. Two or more orders of magnitude below the noise level of their experimental setup.
@ Yup, that’s exactly the one I was referring to. 😁
FIX that burnt resistor on that little board!!!!!
Oh, the discolored one? It's not burned, it's a 1% resistor still within 1%. I had that happen in the HP 3300 repair too. Somehow these high-precision HP blue resistors discolor like that, but it's just cosmetic.
the clock itself is not battery operated. how is that supposed to work ?
The oscillator has a +24V DC output, you can see it marked as "ACCESSORY SUPPLY" in the top corner of Figure 5-15 (11:00). After Marc hints at the clock adjustment procedure (around 31:40), he says that "the 106B came with a battery that could operate both the oscillator and the clock and I really need to get that functionality back." He then goes on to fix the whole battery related stuff, so I'm pretty sure he connected it the way it is supposed to be.
@@federicodidio4891 good spot , also at about 2:10 marc mentions the 'special plug' for interfacing , I presume this does the power as well as whatever else is needed.
Gee the world was small back then, only 11 countries - lol -.
Why is the tube in the atomic cock a finite life item? It's not like the cesium is actually consumed, it's just moved around.
Is there something that makes it cost prohibitive to add something to cycle the cesium back the other way? Or build it so that it can be "regenerated" (e.g. "hold it in orientation X and heat at point Y to temperature Z for Q hours".) That would seem like a highly desirable property for something that costs tens of thousands of dollars and lasts less than a decade. Even if it would double the cost of the tube, that would pay for itself in lest than 20 years.
Comes out of a tiny focusing hole at one end, splattered all over the tube at the other end. You can't just stuff it back in unfortunately. And you can't just open the tube to atmosphere either, or the Cesium will burn or explode in your face. Apparently, even at $20k, it's cheaper to make a new tube than to refurb an old one. I hear the yield on the tubes is low too, these are hard to make! I'm tempted to open one up and try for myself though, maybe I can get help from my buddy Ben Krasnow.
@@CuriousMarcinteresting.
Out of curiosity, I tried to check how much is used (if it's just a drop, I could see even getting it to drain off the far end might be hard) and found an AI generated response referring to "clock that doesn't recirculate the cesium" as using about 1 gram per year.
If that's not a hallucinating AI, that says something interesting right there.
@benjaminshropshire2900 The tube has 7 grams of Cesium, and should last approximately 10 years. AI wasn’t that far off!
Has me wondering how the flight clocks were powered.
Big external power supply box at the bottom with large batteries. You can see it in the flight rack photo.
And people thought clocks were easy. I'm afraid for our next generation who just thinks clocks come from their iPhone in their pocket. *sigh*
Would you rather that technology stood still? Nothing to be afraid of, they live on the cusp of some amazing technology advancements, just as the generation who saw this HP equipment did. The iPhone in the pocket is an amazing example of technology advancements at an astonishing rate, just 40 to 50 years after this HP clock, amazing!
👏👏👏👏👏💯🥇✌🔝😮
hi
First?
Looks like it. You just won a free dubious oscillator power supply modification.
@curiousmarc: I LOL'd
@ yeah!!
@@markgreco1962 but you have to provide your own missing transistors
> Oeven
> Oeven
> Oeven
Its OVEN~!
😁🤣
Non non non. On my channel, it's Oeven.
Over, Oveur.
0.999999 ⓈⒶⓉⒾⓈⒻⒶⒸⓉⒾⓄⓃ