Restoring an HP 150A Oscilloscope (Part 2)

[@MrCarlsonsLab]

Hello. Very nice looking scope! Some observations: The horizontal sweep is not linear, you can see this affect by looking at the screen and seeing that one side of the sine-wave is compressed. This non-linear ramp could be caused by multiple things. Even for a 10MHz scope, capacitor lead length and their orientation in circuit is very important. Chances are, this scope is "just for fun" so probably not to big of a deal. If you want it to operate like it did when it was new, you have some work ahead of you. Good Luck, and have fun!

[@UsagiElectric]

Whoa, Mr. Carlson, hello! (I've been a big fan for a while!) Thank you so much for the tips! You're right that this is definitely a "just for fun" scope, so I'm not really expecting it to get back to 100% - I would be quite happy with "close enough for government work." Particularly, for my uses, I never really do anything over 100 kHz, and I don't think I even have anything that'll generate a signal faster than 1MHz, so the scope is already spec'd well beyond what I'm capable of even testing here. However, I would indeed like to get it fairly close to being right. As I was filming it for this video, the longer it was on, the worse it got, eventually getting to the point where the internal sync stopped working altogether. If you look at 20:46, the sine wave is traversing across the display because at this point I actually had to switch over to the "Line" setting and bring the oscillator frequency down until it kind of settled down a bit. So, I think I've got some resistors that have drifted quite a bit from spec, or may be getting worse as they start to heat soak. It's still a long road to go, but now that it's actually giving me some life, it should make diagnosing it a little easier (I'm hoping at least, haha)! Thanks again for the tips and as always, I'm looking forward to the next video from the lab!

[@paulawillaminachandler-ren3725]

@@UsagiElectric Wooa, is right. This Mr. Carlson's guy knows his stuff. Might want to look into his idea about outside foil when recapping.

[@FordSeniorMaster]

@@UsagiElectric DUDE! You made "The Big Time"! Congrats!!!! When the "Tube Master" comments and shares his EXCELLENT knowledge with a guy, he has made it! Paul Carlson IS the man I would most want to emulate, when it comes to electronics. LOVE your Channel and your content BTW! All the best, Patrick

[@UsagiElectric]

@@FordSeniorMaster Thank you so much! I definitely showed all my friends when he commented, I was so stoked, haha. Mr. Carlson is definitely a huge inspiration and is extremely knowledgeable!

[@georgegonzalez2476]

I am glad to see you didn't try to unsolder the capacitor leads through the PV board. These old PC boards, the copper traces were held on with wishes and fairy tears.

[@UsagiElectric]

There were actually quite a few places through the build that did require me to unsolder the leads from the PCB, and surprisingly, the traces were totally fine! Sure, the PCBs are not as robust as modern equivalents, but they're certainly tougher than I was expecting!

[@EsotericArctos]

The trouble with electronic components, you can't tell by physically looking if they are good or not. the "black beauty" caps are usually a paper / foil type capacitor and they papare has long since started to degrade, creating parallel resistance inside the capacitor, which can cause major problems. One of the joys of restoring this old equipment, but once restored this old test equipment will last you a life time.

[@faisgaffeimbecile1939]

This is the 1st video of yours I've seen. I've not gotten (I'm British but I'll humour it), to the end yet but I'm really enjoying watch you do this refurb. I'm going to be building an all valve transmitter for 160m AM using all original 1963 spec parts so I share your rosy tint view of tube (ahem, valve) techniques but I don't share your hair colour. I dye-refurb my barnet.

[@georgegonzalez2476]

In series heater strings they usually use "A" suffix tubes, which have a specially controlled heater warmup time so all the tubes share the current and have equal voltages while warming up. HP cut a corner here, and it showed.

[@UsagiElectric]

DC heater strings actually make sense in some situations as the AC on the heater can actually influence the cathode and potentially cause oscillations. I think HP was concerned with trying to make it as accurate as possible, and so used DC heater strings. And, given that it has a 30-second time delay to get all the tubes to full temperature before applying any HV, using the "A" suffix tubes was probably not as high of a priority. This scope may not have been the best scope on the planet at the time, but HP certainly weren't in the habit of cutting corners. Personally, I think HP did a wonderful job, and so far, it seems to work excellently! The only drawback so far is that it weighs so much I have to be careful not to blow out my back when picking it up, haha.

[@georgegonzalez2476]

@@UsagiElectric Yes, I have a few large Tek scopes and a sore back to prove it. BTW I was given a HP 170 scope long ago that had not been turned on for like 25 years. Not knowing any better I just plugged it in and it worked perfectly. Well, the fan motor needed a few drops of oil. And the Delco power transistors were a bit leaky. Being HP they overengineered that a bit, making a custom machined heat sink surrounding the fan with what must have been very expensive high-voltage Delco power transistors. Nobody else used transistors as series regulators in a HV supply but that did not stop HP! Regards.

[@frankowalker4662]

So nice to see a trace on the scope. Now the fun can begin with a full repair and calibration. :)

[@UsagiElectric]

Thank you! Yup, as difficult as it was getting to this point, now comes the really difficult part of identifying which resistors drift with temperature, where exactly I'm having little issues, and all sorts of tedious, but fun testing!

[@adailyllama4786]

You always provide such clear and easy to understand overviews. Excellent music too

[@UsagiElectric]

Thank you so much, that means a lot to hear!

[@cathode_gay_tube1312]

im glad i could help ! in the future, always check your power supply rails first! when you checked for signal before even checking the Va i was like :'0

[@UsagiElectric]

A total life saver! Sometimes I get so caught in looking for something difficult, that I totally gloss over the obvious stuff, and it's good to have smart minds like yours to lean on and get me pointed in the right direction again!

[@edgeeffect]

I'm glad he mentioned you by name because that made me go looking for your channel and.... oooooo..... you've got scope art.... gotta come over and check that out.

[@BruceNitroxpro]

If you follow Mr. Carlson's Lab, you won't make any errors that may make getting new parts necessary, such as doing wholesale cap replacements of ALL old equipment (unless some micas are left in). Checking using a Flir device will spot cold tubes. Or other simple ways, such as simple meter checks of filament strings.

[@UsagiElectric]

I do indeed follow Me. Carlson's Lab, but I also do have to work within the limits of my budget and goals for the project. I'm not expecting the scope to ever get back to perfect accuracy, but I am hoping to bring it in spec. But, some things are just not feasible. A Flir camera for example costs about three times what I paid for the entire scope. Blanket cap replacements aren't always the best solution (though in this case, I've pretty much already replaced every cap that wasn't a Mica). But mostly, I'm really just having a ton of fun following errors and problems through the system and fixing the parts one by one. And fortunately, that's let me catch some parts that I wouldn't have caught otherwise, like poor emission on a horizontal amplifier tube or a bad thermistor on the 400V rail.

[@BruceNitroxpro]

@@UsagiElectric , I guess ya gotta do whatcha gotta do. Good luck!

[@SeltsamerAttraktor]

Really good choice of music!

[@UsagiElectric]

Thank you! Interestingly, the music has been the most polarizing aspect of this video. I put music in almost all of my videos, but the one in this video has gotten several comments of people saying they really liked it or they really hated it! I'm a bit surprised that it's garnered that much attention, haha.

[@SeltsamerAttraktor]

@@UsagiElectric The typical royalty free "retro video game" music tracks that everyone uses really started to grind my nerves. So some pokemon tunes are quite refreshing to hear :3

[@paulawillaminachandler-ren3725]

I bet it's going to be a lot of drifted resistors causing those problems, and possibly dirty pots too. And just thinking my old scope has only 8 tubes inside. That scope is an absolute beast. I am enjoying this restoration. Nice job so far.

[@UsagiElectric]

Thank you so much! I think you're absolutely right on the resistors. It was actually working much better at the start of filming, but after about an hour of on-time, it was becoming more and more finicky, and more of the scope stopped functioning. If you look at 20:43 in the video, the trace is actually scanning across the scope, and that's because after being on for an hour, the trigger had very nearly quite working altogether. I had to switch it over to "Line" and then adjust the frequency of the oscillator until I got the waveform frequency and line frequency to nearly line up. So, as it gets hot, I've probably got some resistors drifting quite far out of spec and causing issues. Now, tracking those down is going to be an interesting exercise that I'm sure will turn my already grey hair even more grey, haha.

[@paulawillaminachandler-ren3725]

@@UsagiElectric Thanks for the lengthy comment, I like reading as a hobby. I guess old carbon resistors would be the only logical conclusion. I've seen a lot of Shango066 videos so I guess I picked up a few diagnosis tricks, plus it precision tube equipment, caps and resistors would matter more, than in radios and tv's. Speaking about caps why didn't make a J-hook when you were installing the new ones, these new lead free solder tend to melt at a lower temperature. Well your content is super educational, and entertaining. I can't wait to see more on this unit. Oh, and I love your hair. I am sure all your subs do as well... It makes you appear sorta like that Ancient Aliens guy, But instead of aliens, Ancient Electronics... Besides Weird hair make one look more Intelligent. Like that German guy with his fake relativity theory LOL!

[@UsagiElectric]

@@paulawillaminachandler-ren3725 I'm with you and leaning much more towards the resistors drifting as being my primary problem here. Unfortunately, there's about 500 resistors in this thing, so it's going to be pretty tedious to find the right ones, haha. As for the caps, I don't really have a great reason why I didn't do a J-hook, other than that the 90* bend I made was easy to bend up like that and still held the caps in place while I soldered them in. As for solder, I'm actually using 60/40 lead tin, which seems to flow and work really well! Thank you so much for the compliments on the content! And thanks for the compliments on the hair too, haha. I do indeed definitely resemble the Ancient Aliens guy a bit, especially how his hair got crazier and crazier as the series continued.

[@ad5mq]

don't feel bad! I once spent half a day trying to diagnose a tv that wouldn't do ANYTHING, finally checked the fuse, and, of course, that was the entire issue.

[@UsagiElectric]

It's funny because the first advice I give to anyone is to check the cheap and easy stuff first. Then, when it comes time to diagnose my stuff, the cheap and easy stuff is always the last stuff I check, haha!

[@m.s.m8918]

Such cool equipment!🥲

[@UsagiElectric]

It really is a gorgeous scope! I still have a long ways to go, but I'm quite happy with how it's coming along!

[@rrb6544]

Wow those neon voltage ref, lovely!

[@UsagiElectric]

Those neons are truly gorgeous aren't they!

[@jonka1]

Running heaters in series. You say they must be the same voltage and current. Try revisiting that statement. The only requirement is that they must be the same current. Lower current heaters can be used with a parallel resistor to compensate. You assume that the heater went open and then the resistor smoked. Maybe the resistor was high and this caused the pre-stressed heater to blow. Assumptions are dangerous . A visual inspection is never time wasted and you might have seen the resistor was already cracked, just as two minutes with a voltmeter would have lead you to the voltage settings for the mains transformer.

[@akkudakkupl]

Very good job on changing those bumblebee capacitors :-) I'm quite sure any one of those in the wild have failed or are very close to it.

[@paulawillaminachandler-ren3725]

They fail shorted too, so not just magic smoke. Magic boom.

[@UsagiElectric]

I'm glad they were pointed out to me, at first glance I totally thought they were alright as I was looking for leakage from them, I totally missed the cracked casing. I do feel a lot more comfortable powering it up now with the new caps in place though!

[@tstahlfsu]

Super cool to see it working! I can't tell you how many times I've let the smoke out haha

[@UsagiElectric]

Thank you! Sometimes it's good to let the magic smoke out, so you can put new, fresh magic smoke back in, haha.

[@edgeeffect]

Watching DiodeGoneWild fix a vintage TV recently... he was "concealing" modern small caps inside the busted cases of the old ones.... the finished result is "almost authentic"........ but I suppose that only really works for electrolytics.

[@UsagiElectric]

I've seen quite a few people do that before too! It really does help maintain the original appearance. For this one though, the big metal can caps were hidden deep inside, so I wasn't too worried about aesthetics. Plus, I think the PCB version with the new caps on it looks pretty cool in its own right too, haha.

[@diskcopy]

Nice job so far!

[@UsagiElectric]

Thank you so much!

[@treadmillrepair754]

Amazing piece of technology and excellent job. Best Regards

[@UsagiElectric]

Thank you so much! It really is a cool bit of history!

[@ArtemKashkanovLive]

Heavy duty scope! Nice job done. So many PCB inside - My TR4401 has no PCB inside. 3D wiring only.

[@UsagiElectric]

Thank you! And emphasis on "heavy," I nearly throw my back out everytime I lift it up onto the table, haha. I think the 150A was HPs first scope to use PCBs. The manual has a dedicated section on how to repair components on PCBs even. The TR4401 must be a really, really rare scope! I tried to find some pictures of it, but there is practically no information out there on the scope, that's awesome that you have one!

[@ArtemKashkanovLive]

@@UsagiElectric Mine is also not too heavy. Only two man needed to carry it. Thats why it has two handles. here are some photos: dekatronpc.com/index.php/EMG_TR-4401

[@UsagiElectric]

@@ArtemKashkanovLive That thing is awesome! It almost looks like it was meant to be a competitor for some Tektronix scopes, at least the design looks pretty similar. Even the terminal strips for the passive components on the inside is very Tektronix feeling. Still, absolutely beautiful scope!

[@ArtemKashkanovLive]

@@UsagiElectric Yep, It's a Tektronix 541A copy.

[@Pamberjack_]

I’m hooked. Subbed.

[@venus007e6]

When you were switching out all the caps, what was that pink thin tape you were using whilst putting in the 2 caps on the backside of the pcb?

[@jeldrikpetersen]

Did you pay attention on the foil end of those foil caps? Allways keep in mind to put the outer foil end to the lower impedence section regarding Gnd!

[@UsagiElectric]

As near as I can tell, the Panasonic film capacitors that I'm using don't have any indication as to polarity or which end is the outer foil. I read through the datasheet looking for any of that information, but maybe I overlooked something? www.mouser.com/datasheet/2/315/ABD0000C179-947645.pdf

[@jeldrikpetersen]

@@UsagiElectric Modern caps are not indicated but still have the outside foil end. Either you test with your oscilloscope for frequency response or with Mr. Carlsons genius tester. I use my oscilloscope as you have to get the shematics from his patreon and build the device by yourself. I see forward to join his classes on patreon. The scope method is cheap as you have one but it really is a pain in the a** for caps smaller than 10 nF and you really need a sensitive Scope with following 1. at least 5 mV sensitivity and 2. 1:1 Probe. Bandwith is not that important as you use your Body as Hum antenna 1 MHz is sufficient. You should really follow Mr. Carlson he's THE guy if it comes to tubes. kzbin.info/www/bejne/eJ-1kHeCmZaDeqs

[@Sine1040]

@@jeldrikpetersen Not that it really matters in this instance

[@jeldrikpetersen]

@@Sine1040 Why shouldn't it matter? An oscilloscope should be precision equipment as it is designed to be. As you use it for RF measurements you should guarantee signal integrity. To start with even the smallest passive parts like caps. Why should one want to screw up measurements by insufficient repairjobs. In my opinion one has to do the job right or just don't touch it!

[@Sine1040]

@@jeldrikpetersen This is a good old (but slow) 10MHz scope, you are not going to do HF things with it. Plus the caps are in the horizontal section / timebase where it's even less of an issue.

[@lunaroja4703]

Amazing

[@UsagiElectric]

Thank you!

[@yakovkonovalchukov2400]

"Here comes the warm machine Such a warm machine" (c)

[@UsagiElectric]

Oh man, it's so hot! During filming I had the machine on for about an hour straight in my tiny little room and I was sweating buckets by the end, it was overpowering the air conditioner, haha.

[@MAYERMAKES]

that reminds me of the old scope I wanted to repair 5 years ago...it is still waiting on the shelf

[@paulawillaminachandler-ren3725]

I guess it will never be repaired then. Usagi is obviously a functioning lunatic...LOL. Unless you are one as well that scope will remain shelved. :)

[@UsagiElectric]

Ah, that's a "one of these days" project. I got a bunch of those, haha.

[@UsagiElectric]

@@paulawillaminachandler-ren3725 Functioning lunatic, I like that!

[@paulawillaminachandler-ren3725]

@@UsagiElectric Excuse the vernacular but... Can you blame me? You are doing some really un-thinkable stuff with tubes. A 1-bit processor. A 555 timer from tubes, Not to mention making them work and a ridiculous lower voltage than recommended. Who in the world does that? LOL!!! Besides... That was a compliment hun.

[@UsagiElectric]

@@paulawillaminachandler-ren3725 Oh, I totally took it as a compliment! Functioning lunatic is very much so my wheelhouse, so to speak! When I'm building these things, I'm often thinking "This is quite mundane stuff, I'm not doing anything too crazy, so this is probably going to be a bit of a boring project." but when you say them out loud, it does sound a little insane, haha.

[@VandalIO]

I was wondering most of the inverter circuits are based on solid state electronics , is it possible to build an dc to ac inverter using vacuum tubes ?

[@UsagiElectric]

I might be inclined to say that most solid state electronics are based on vacuum tube circuits, since these designs all predate the transistor by a fair amount! But, that may be me being a bit pedantic, haha. At any rate, it is definitely possible to generate AC waveforms from DC using vacuum tubes. But, they're going to be fairly low current simply because vacuum tubes just can't move that much current. One design that is really easy to build, is a multivibrator. IBM used this basic design in monostable, bistable and astable for most of the building blocks in their old vacuum tube computers. Here's the basic multivibrator astable design: i.postimg.cc/kXzBr3zr/103078864-10221111567233036-448440687881355264-o.jpg I actually use pretty much the same design only at 12V in the little flashing rabbit logo I built for the new intro. But, there's a ton of other great oscillator designs out there, like the Hartley oscillator or the Wein Bridge oscillator!

[@VandalIO]

@@UsagiElectric thank you for a detailed response and pointing me to the right direction … I will explore this in more details

[@JWimpy]

At least if your heat goes out this winter you can just fire up the 'scope.

[@UsagiElectric]

No joke! Every time I start filming, it's nice and comfortable in the room, but when I finish filming I'm drenched in sweat from the heat this thing puts out, haha.

[@mikeringer1]

Anyone know how many 12ax7s are in the 150a?

[@johnscoles660]

Hmm not 100% sure here but I think you should of replace those Bumble-bees with 'Metalized Polypropylene Film' axial caps , rather than brown drops? That could cause the problems that Mr C has comment on. The adage 'A capacitor, is a capacitor, is a capacitor' is not true in this case.

[@UsagiElectric]

For the time being I think these caps are going to be alright while I diagnose some much larger issues with the system. The longer I use the scope, the worse it gets, so I'm pretty certain that I have some resistors that are drifting further and further out of spec as they heat soak. I'm fairly certain that this is what happened to R132 which caused the 6AL5 to pop - it drifted so far that too much current was being pumped the heater causing it to break open, which then left the only path for current through the resistor, which caused it to burn up. Once I've eliminated all other obviously bad components and the scope is functioning quite reliably, I'll get into trying to bring it back into spec. At that point, if the caps are proving to be an issue, I'll definitely look into getting more appropriate axial caps with the proper lead lengths. Gotta tackle the big, immediate problems first though!

[@johnscoles660]

@@UsagiElectric Good to know! Remember that to get this back to 100% spec you will have to install any of caps that replaced the 'black beauties' will have to have the 'foil' side toward ground. Even your brown drops will have a 'foil side'

[@w2tty]

I’m enjoying this series. I see you put something white between the board and the capacitor and then remove it. I’ve never seen anyone do that before. What is it? (PS. If you explain it later in the video, I missed it)

[@UsagiElectric]

Thank you so much! As for the white thing, it's actually really trivial, haha. The new capacitors are so much smaller that there is a lot more exposed lead. In some places the more exposed leads got a little close to the leads of other components for my liking, so I just folded up a piece of paper to act as a spacer. I popped the paper spacer down, set the cap on top of it and then pulled the paper out after soldering, which would elevate the capacitors up a bit and keep the leads clear of everything. If you look at C93 shown at 5:50, you can see how it sits proud of the PCB by a few millimeters. Getting the capacitors to sit at about that height was really the only purpose of the white paper!

[@mominkhan7247]

nice

[@bronka42]

beware of falling into the rabbit hole of analog electronics ... it can be a real nightmare and an obsession for life. you're going to need a big bottle of magic smoke!

[@UsagiElectric]

Nightmare is definitely right! But you might be a little late on your warning, I'm already obsessed for life! Now to find out where to order the premium magic smoke, haha.

[@bronka42]

@@UsagiElectric next proyect....vaccum tube analog computer?

[@UsagiElectric]

@@bronka42 Surprisingly (or maybe not so) that's been on my little Excel sheet of projects to do for quite a while now! One of these days, I'll get into it properly!

[@rrb6544]

The very first!,

[@UsagiElectric]

This is about as "first" as it can get!

[@sjenkins1057]

Music unbearable. Please, please, silence, or narration, or bunny noises.

[@UsagiElectric]

I'm sorry you didn't like the music. Usually I play music during my timelapses and it's never really been a problem before, but this song in particular seems to be very polarizing. I've gotten a lot of comments by people saying they hate it and by people saying they love it. Either way, the music isn't supposed to be the main focus, but rather something to fill the silence during the timelapse, so I most likely won't use this particular song again.

[@pahaahv]

There's a mute button on the left of the KZbin video controls bar. I liked the song.

[@sjenkins1057]

@@pahaahv Mute is not an answer, as then you miss the narration when it returns.