Restoring an HP 150A Oscilloscope (Part 1)

[@malcolmholmes115]

I can feel the smell of old electronics dust through KZbin video. If someone spent their childhood by digging into the vintage hardware, they will understand what I mean. This smell can’t be confused with anything else.

[@UsagiElectric]

Absolutely! It smells exactly as you're imagining it, and while most would say it smells bad, there's just something fantastically nostalgic about that smell!

[@adityatyagi4009]

I am so glad to have come across this series of videos. I have had an HP 175A oscilloscope in my possession for many years now and am looking to restore it. It worked perfectly fine last time I checked and I hope it still does!

[@dans8287]

I don't know if I should congratulate you or give you my condolences for getting the tube hp scope? I ended up getting 2 tube scopes one is a Sylvania 132 I picked up at a antique mall. It was a total recap job and its a very low spec scope that probably cost a fortune when it was new. I couldn't resist the art deco styling it just looks so cool. I also picked up a Textronix 310a at a hamfest for super cheap. It had a shorted filter cap which caused a resistor to let out the magic smoke. It is all point to point and uses these weird porcelain terminal strips with silver terminals. I found that the silver starts to migrate across the porcelain and causes intermittent noise. If you ever pick up one of these you have to use silver solder if you change any components that attach to the porcelain terminals. Despite all of its problems its a cool scope since the outer case is full of ventilation holes so you can see all the tubes glowing. It also makes for a decent space heater too. haha

[@UsagiElectric]

Haha, interestingly, I was actually going to pick up a Tektronix 515A, but the guy I was getting the Tek from mentioned in passing he had an old HP all tube dual channel. I kindly set the Tek down and managed to talk him out of the HP one. Mostly, I really wanted an all tube, dual channel scope, and I wanted one that would match my all-tube HP signal generator, so this big beast ticked all the boxes! Now, I just gotta get it working right... I had to look up that Sylvania scope, that is an absolutely gorgeous design! Like you said, that Art Deco look is just so cool. Tektronix had really wild construction techniques. We had a 545A that a mouse had made a home inside and absolutely wrecked it, so we salvaged it, and it's the only piece of equipment I've seen to use those wild porcelain terminal strips. I imagine they're an absolute bear to repair. The good thing about the HP scope is that it's all on PCBs that are really clearly labelled, so I should be able to test voltages and waveforms at various spots to see where the faults lie. That would be a nightmare to try to figure out on an old Tek scope! Though, in Tek's defense, I think their scopes were generally so reliable they didn't need much repairing, haha.

[@AlejandroLopez-qd3xm]

@@UsagiElectric Teks are all right!, but better leave them to Mr. Carlson! He's got a garage full of them!

[@dans8287]

@@UsagiElectric I'm not sure if they are new old stock or if antique electronic supply found someone who is making them but check this out. www.tubesandmore.com/products/terminal-strip-ceramic-1-row-4-slots-25mm-thread

[@UsagiElectric]

@@AlejandroLopez-qd3xm Oh man, Mr. Carlson's latest video is insane! I knew he had a lot of Tek gear, but man, I had no idea. That's a proper collection!

[@UsagiElectric]

@@dans8287 Whoa, that's awesome that someone still has some available. They're not cheap, but they'd be perfect for someone looking to restore a rare piece of Tek gear!

[@gammaleader96]

Very nice, a lot of old HP service manuals had a section on theory of operation and circuit design, making them almost a kind of educational book for designing the equipment.

[@UsagiElectric]

Thank you very much! The service manual for this scope is awesome! Like you said, it's got a huge section on theory of operation and then some excellently comprehensive schematics with little waveforms and voltage levels to make trouble shooting so much easier. It truly is a testament to a time when engineers were a higher rank than accountants!

[@senilyDeluxe]

"Behemoth of an oscilloscope" Laughs in Tektronix 535

[@UsagiElectric]

Oooh, the 535 is a gorgeous scope! Though, be careful not to throw your back out lifting it around, haha.

[@senilyDeluxe]

@@UsagiElectric It's not as heavy as it looks. Still pretty heavy though. And unwieldy. And you can kill someone by dropping it on him. I need to get the vertical deflection plugin working on mine though. I found it on the curb, had to replace a voltage regulator tube that went to air and now it works if I remove the plugin module, albeit useless without vertical deflection but at least I know the bulk of the machine works fine. The trace was really bright and sharp with the controls in center position!

[@AlejandroLopez-qd3xm]

What a nice piece of equipment to troubleshoot! That should be a lot of fun.

[@UsagiElectric]

Thank you! So far I've learned an absolute ton about how the scope was built and laid out, and it's been a blast digging through the schematics (if not a bit overwhelming, haha).

[@YesterGearPCii]

I've got a Tektronix 7704 from '69 that I'm working on as time allows. All gold traces, wire-wrapped posts everywhere, it's a nightmare lol. Has no horizontal sweep currently. I'll get her going right someday.

[@UsagiElectric]

Very nice! The 7704 had that epic plug-in module system that really gave the scope a lot of flexibility! That's a really cool scope and should be a ton of fun once up and going again. The trick is trying to keep up with Tektronix's wild build quality, haha.

[@YesterGearPCii]

@@UsagiElectric She seems to work okay except the display is compressed, and there's no horizontal sweep. Vertical seems fine. Even the "digital readout" at the top and bottom shows up well, and reads correctly when given a static voltage. CRT control needs some love, as does the horizontal circuit for the sweep. It's a "someday" project. I have a Tek 485 and a Sencore Widebander that work perfectly, so not in a rush.

[@UsagiElectric]

@@YesterGearPCii The digital readout of the 7704 looks so amazing because it looks like it's drawing it with scope. The internal circuitry for that must be absolutely mental! I hear you on the "someday" projects though. Honestly, this 150A would probably be a someday project, but I really wanted a proper all tube scope to use for my tube projects, haha.

[@diskcopy]

Hey, someone else has a 150A too! I have been working on restoring one (very slowly)...have to fix the power supply, and probably everything else ;) From what I have read, these are sort of rare now, as HP had reliability issues with this model. This was also one of the first scope HP made, introduced along with the 130A. Congratulations on your find, and I'm looking forward to see how the rest of the restoration goes.

[@UsagiElectric]

Whoa, another 150A owner! I'll be honest, I didn't anything about this scope when I picked it up. I was actually going to buy a Tektronix 515A, and the gentleman mentioned in passing he had an old all-tube HP dual trace scope. I set the Tek down and managed to talk my way into getting this one of his hands. As you said, it seems these are pretty rare! HP was aiming at taking on Tektronix's flagship models, but HP found out the hard way that that was easier said than done. I'm curious as to what kind of reliability issues they had. Most of what's wrong with mine seems to be age related, since most of the components are now 60 years old. Hopefully, as I get further into troubleshooting, I'll get a better idea of any weak points!

[@diskcopy]

@@UsagiElectric Be careful when replacing components on those circuit boards. PCB technology was new, and the pads and traces will lift with too much heat. On my 150A, I was able to reform the electrolytics, but I liked your drop in replacement board.

[@UsagiElectric]

@@diskcopy My current plan when replacing the black beauty caps is to snip the legs of the old caps and solder the new caps to the remaining bit of legs on the boards. I want to avoid de-soldering and soldering to the PCB as much as possible! Once I'm sure the drop-in electrolytic cap board is working well and not going to have any issues running for extended times in the machine, I'll post up the gerber files, so anyone needing to replace the electrolytics in their 150A can drop in the board with relative ease!

[@diskcopy]

@@UsagiElectric Good thinking on those caps. For those old boards I like to use a vacuum desoldering pump, which doesn't put lots of stress on the board. On my 150A, there were a bunch of 6KV paper caps on the high voltage board that needed to be replaced. They have yellow printing and are leaky like the others. After I clear some other projects out of the way, I will finish restoring my 150A, and after that there is a Tek 585, which I am excited about working on too.

[@UsagiElectric]

@@diskcopy Oooh, I'll have to check the HV portion for any of those caps. Fortunately, the HV all seems to be working good for now, but I'll definitely take a look-see because paper caps aren't the most reliable things out there.

[@lelandclayton5462]

you're in the right direction so far. Might want to replace some of those black beauty caps and test the tubes in the HORZ circuit.

[@UsagiElectric]

Thank you! Yup, those are on the list of pieces that need to get attention. Some of them look pretty bad with cracks in them, but I still need to go through and write down all the proper values and get an order in for good replacements. I wanted to fire it up and make sure that the CRT was good and that the low voltage and high voltage power supplies were all working first though. I'm pretty optimistic that it'll get right back up and going without too much more work though!

[@drPeidos]

I've already said it in other of your videos, and I say it again for this video: Good choice of music :)

[@lindoran]

I've watched this 3 times now, some real good film making here; also Chrono Trigger, nice choice!

[@UsagiElectric]

Thank you so much! And that Chrono Trigger track is epic isn't it, haha.

[@lindoran]

@@UsagiElectric these videos have been a really good way for me to connect with my dad he's an electrical engineer who had his start in sparry UNIVAC prior to being drafted for the veit nam war, then after his 4 years were up he got his ee degree from unh and went on to work for ge in the 70s 80s and 90s designing medical equipment. Such wonderful videos thank you for doing them I'm learning so much 😁

[@UsagiElectric]

@@lindoran Oh man, that's awesome that he worked for UNIVAC, they made some of the coolest computers in the 50s, 60s and 70s! That's amazing to hear that you guys are enjoying the videos together! The community that has come together over these videos has been absolutely amazing and has made making the videos more than worth it.

[@arianont]

Agree, sold at the Chrono Trigger track

[@glufke]

That's extremely cool...

[@UsagiElectric]

Thank you very much, I think it's one of the coolest pieces of old test equipment I've managed to get my hands on!

[@tedrobinson372]

My 1954 RCA CT100 uses about 8 6AN8s. There are tons available on eBay.

[@ad5mq]

look carefully at out of tolerance resistors - especially in timing parts of the sweep circuits. I restored a Tektronix scope of similar vintage many years ago and had lots of issues with resistors which had wildly out of spec values, also resistors whose value shifted as they heated up.

[@UsagiElectric]

Interesting! I hadn't thought of resistor values changing as the machine gets warm, but that makes total sense! My first order of business is tackling the old "black beauty" capacitors though. There's quite a few of them in there, and at first glance they looked alright, but upon closer inspection quite a few of them are cracked down the side, so I'm thinking they're probably contributing to the weird behavior I'm currently seeing.

[@JamrockVybzTV]

Great job fam

[@frankowalker4662]

What a gorgeous scope. I noticed at around 15:02 the trace jumped when you held the scematics up infront of the screen. (?) It looked odd.

[@UsagiElectric]

Thank you! It did indeed jump around. It was a little unstable and sometimes just tapping it would cause the trace to wobble a bit, so something isn't quite right in there and heat, movement, air, etc. is enough to upset it a little. I'll just take it step by step until we get back up and going though!

[@frankowalker4662]

@@UsagiElectric I'm looking forward to future parts. :)

[@shyleshsrinivasan5092]

Really glad to have found this video !

[@UsagiElectric]

Thank you for checking the video out!

[@Sine1040]

With these voltages you might want to have a bit more clearance on the cap board. I wouldn't make them smaller than 3mm.

[@UsagiElectric]

The capacitors on the PCB are all for the low voltage power supply actually, so there's not anything to aggressive on their. The biggest voltage difference is around 350V, but the rest are around 200V. The recommended spacing for that is about 2.5mm and while I'm a little under that, I haven't seen or any arcing or anything yet. I should probably coat the board in a conformal coating or something, but I'm still keeping it open until I'm sure I've got everything hooked up just right. All the really high voltage stuff is contained in a little box in the back that I'm trying my best to avoid, haha.

[@beakytwitch7905]

And / or paint some insulating varnish on to prevent tracking...

[@mylestechnological7031]

I'm normally the first one to watch your videos when I see them pop up in my notifications

[@UsagiElectric]

Thank you for checking the videos out!

[@markkamrowski1293]

Funny how the universe works... just got a 150A working last weekend and I came across your videos. My scope had a low voltage (LOL) power supply issue that took me a few hours to figure out. Mine seems to be different from all the others in that it has a purple/blue colored phosphorus CRT. Both channels work on mine but my calibrator voltage doesn't quite reach a 100 vpp. Might just need the pot tweaked. I traded a guy a Simpson 260 VOM even up for it 30 years ago. I wanted a scope so it seemed like a fair deal even though I could borrow one from work. Incidentally, mine doesn't have the case so If anyone knows where I could find one...

[@UsagiElectric]

Another with a 150A! It cracks me up that the low voltage supply still supplies like 400V+, haha. It seems the 150A had a few different phosphor options, and the scope itself is rare enough that I haven't even seen any pictures of the phosphors other than the green one like mine. This one is still giving me some trouble, but I'm slowly learning my way through the insanely complex analog circuitry that's going on inside. Still, if it weren't such a gorgeous machine, I may have given up on it, but I'll go out there and say it's a better looking machine than nearly any Tek scope (though, maybe not nearly as reliable, haha).

[@MaxKoschuh]

wow, this is wonderful! Great video !

[@UsagiElectric]

Thank you so much! I really love HP's aesthetic for their equipment from the 50s and 60s!

[@stphinkle]

I would check to see if there are any paper wax capacitors. Those should be replaced if there are any as they are prone to failure and leakage over time. I would also be very careful as that CRT may have thousands of volts on it, ewowcially on the Anode, and on the Damper, Horizontal Output, and HV rectifier tubes. I would also use a variac to power that up the first time and make sure there are no shorts.

[@UsagiElectric]

Fortunately, there aren't any paper wax capacitors inside this one. I'm well familiar with those types being a nightmare, as our Magnavox concert grand had a bunch of them, and they were gross and dead! Unfortunately, this one has quite a few "black beauty" caps, with many of them appearing to be cracked, so they will most likely all need to be replaced. I've got some new modern Panasonic caps on the way to replace those, so I'm impatiently checking the mailbox every few hours until they get here, haha.

[@tstahlfsu]

sweeeeet. Can't wait to see it working!

[@UsagiElectric]

Thank you! I can't wait to see it working too, haha.

[@beakytwitch7905]

What do you reckon to building transistorized boards to replace most of the internal boards? Outwardly the scope can be gotten working, look undisturbed, and work a lot better. And in the action of studying and making transistorized boards you/we might be able to make limited quantities of boards to sell to other people who have junk, nonworking scopes sitting around....

[@UsagiElectric]

Well, honestly, this scope isn't really all that far away from working reliably again, and these old HP and Tektronix scopes were surprisingly accurate. This one has some black beauty capacitors that are split, so that's probably contributing pretty heavily to why things aren't working at the moment. I've got replacements for them on the way that should get here today! As for transistorized boards, it would be very difficult to get working correctly because of the standard operating voltages. This particular scope uses +400V, +260V, +130V, -82V, and -150V (and 4800V for the CRT). In order to get any transistorized boards to work, the entire scope would essentially have to be rebuilt from the ground up. And truthfully, IC or transistor analog scopes are really pretty affordable and beautiful machines in their own right too! Something like the Tektronix 450 series of scopes or the HP 1200A are brilliant scopes!

[@beakytwitch7905]

@@UsagiElectric Yes. For your O'scope in its partially working condition I agree. I am actually working on making transistorized boards for several miniature vintage O'scopes. But don't hold your breath as it will take awhile...

[@UsagiElectric]

@@beakytwitch7905 I think the smaller and simpler the scope, the better a transistorized board for it would be. For example, my Telequipment D52 is a terrible tube scope, but could end up with a massive bump in usability with some transistorized boards and modern updates! Good luck with your boards, and keep us updated, I would love to see them once they start nearing completion!

[@beakytwitch7905]

@@UsagiElectric For anybody interested, try a 1980s japanese made scope's service manual and the book "Know Your Oscilloscope" 4th Edition Middleton. The manual gives component values, the book describes in detail a Heath scope, similar circuitry, without component values. Most of the circuitry can be powered from stabilized plus and minus 8 Volts generated with two opposite doublers from the 6V3 AC heater winding. Its the driver transistors that get a bit trickier, but heck you're already most of the way there. Then think about using a microcontroller for sweep generation - thats when the real possibilities knock your socks off ! .... :-)

[@lindoran]

This is so amazing

[@UsagiElectric]

Thank you so much!

[@Dr3x0w]

Are there any nasty PCB caps in there?

[@UsagiElectric]

There's quite a few "black beauty" caps, and at first glance they look alright, but upon closer inspection some of them are cracked, so there's a good chance that quite a few of them have gone bad and are contributing to my problems here. I've got replacements on the way that should get here today!

[@sjenkins1057]

Bunny steals show...

[@UsagiElectric]

Every single time! But, I'm alright with her upstaging me, haha.

[@dng88]

Interested in the modern one. What should be the first modern oscillator recommended for beginner just probe around circular (especially the breadboard vacuum tube amplifier ... )

[@UsagiElectric]

The modern scope is a Siglent SDS-1202X-E (siglentna.com/product/sds1202x-e/), but it's not exactly a cheap scope. Honestly, I would recommend grabbing an older Tektronix from the 70s or 80s. The Tekntronix 2000 series look to be pretty good little dual trace scopes (like the 2215, 2230, etc.). If you want a storage function, the 5000 series of scopes also look like they could work well (like the 5111, 5113, etc.). HP also made some brilliant scopes in the 70s and 80s too, but I know even less about them. Still, something like the HP 1220A or 1740A looks like they could be pretty solid choices. Personally, I'm a fan of how the HP 180A scope looks! I would just hop on eBay, search for "Tektronix Oscilloscope" or "HP oscilloscope" and then set the price range to what your budget is. Most of their analog scopes should be totally fine for nearly anything you need to do with a scope! If you need a storage function, which is pretty much the only time I break out the nice Siglent, both HP and Tektronix had good storage models in their lineups. Hope this helps!

[@robot797]

interesting also I am amazed that you didnt use hamerite for the case

[@UsagiElectric]

Thank you! Interestingly, the color and paint type was essentially decided upon based on what I used on my 200CD Wide Range Oscillator. And I restored that one during the peak of the pandemic, so I just used what I had laying around, which was olive drab army green spray paint. It came out looking pretty nice and unique, so I figured I would continue the theme on the big HP scope too!

[@robot797]

HAHAHA in that case it fits

[@beakytwitch7905]

@@UsagiElectric yes, and it helps to paint it down, not make it too pretty.

[@thatampguy]

Everybody needs a late 50s or 60s a silos scope with around aperture. There’s just something sexy about it. Leave the graticule off and just enjoy it naked.

[@maxs.3238]

Told ya it would be an HP. Thrilled as fuck for the video, you've just made my evening even better✌️

[@UsagiElectric]

You nailed it! I'm glad you enjoyed the video! I've got some parts on order that should get here soon so I can hopefully get the scope back up and going soon!

[@hugoflores5806]

Did you find a service manual?

[@UsagiElectric]

Yup, the HP archive has most manuals for old HP equipment and so I've been using that one to guide me through most of my troubleshooting process! The schematics at the end are the most vital portion though since the manual doesn't really have much in the way of troubleshooting information. This is the manual I've been using: hparchive.com/Manuals/HP-150A_Manual_Serial_Above1190.pdf

[@hugoflores5806]

@@UsagiElectric That's nice! Thanks for the link

[@georgegonzalez2476]

A long way back our lab got a pallet-load of HP scopes, ex from NASA. Weird scopes, not at all in the HP tradition. The 130's had lots of phenolic PC boards and series-string heaters! The 120's only slightly better. Not at all top-notch in design and quality. Only notable by comparison to Tek scopes which were better in every way. I hear that the HP-150's were a bit of disappointment too.

[@UsagiElectric]

I can't really say much as to the reliability, because the history of this 150A is a total mystery, though it does appear to have been stored in not-ideal conditions. However, now that it's up and going, it appears to be dead reliable and super accurate! But, at the end of the day, what really matters is that I absolutely adore the scope and it's become my primary scope, I use it all the time!

[@georgegonzalez2476]

@@UsagiElectric Yes, there better ones are amazing. I used an HP 170A for several years as my second scope and it was always bright and stable. However eventually the CRT accelerator power supply burned up and the HV transformer was unavailable.

[@KolliRail]

Wow!

[@UsagiElectric]

It's a really great looking scope, isn't it!

[@mchavez56]

well those electrolytic caps were probably bad anyway. as someone says below those "black beauty" caps probably more resistor than cap......but maybe.....of course I watch Paul Carlson's videos too often .....have you seen his latest ....he is a test gear freak!

[@UsagiElectric]

Yup, those black beauty caps are on the list too! I was hoping to not have to replace them because there's about 15 of them and I was being lazy, but upon closer inspection in my troubleshooting, some of them are cracked, which means they're probably no good anymore. Hopefully, with those replaced and a new 6AN8 in place, we'll see a bit of an improvement and can go from there! Mr. Carlson's newest video of his garage is an insane one! I knew he had a lot of gear, but man, I had no idea just how much. He's truly the Tektronix master!

[@belesiu]

Love your channel. Started at H-P way back when and always was impressed with their documentation. Where did you get the schematics for HP 150A scope? I’d like to follow along.

[@UsagiElectric]

Thank you so much! HP's documentation is really top notch! It's been an absolutely lifesaver having the schematics at hand and their excellent troubleshooting and adjustment procedures. The manual for the 150A I found over on hparchive.com. I'm using this manual specifically: hparchive.com/Manuals/HP-150A-AR-Manual.pdf That's awesome that you worked with HP! The more I learn about HP, the more I really feel like they encouraged good teamwork and camaraderie with their employees, which was reflected in the quality of their products.

[@Very_Dark_Engineer]

That little scope should have wheels, engine and personal road or railroad)

[@UsagiElectric]

No joke! Just two weeks ago, I threw out my back lifting this thing around. Took me a few days to recover. I'm definitely going to have to build a roll around cart to house all my vintage test equipment one of these days!

[@Very_Dark_Engineer]

​@@UsagiElectricBe careful with heavy equipment.

[@Pamberjack_]

Paint FIRST!? #schoolboyerror - Also, great video. 😊

[@lindoran]

Really the only thing that makes sense is vacuum tube space war once you get this going

[@UsagiElectric]

Oh man, trying to build a full tube computer that would be equivalent in power to the transistorized PDP-1 would be a serious(ly cool) undertaking!

[@dng88]

I thought it is electronic! Of course it must be tube ...

[@UsagiElectric]

Yup! I was specifically hunting for an all-tube scope! I was initially going to pick up a Tektronix scope, but the gentleman mentioned in passing that he had this old HP scope, and I was completely in love with it the moment I saw it!

[@amirrezasherkoshan169]

Hi sir Can you intrduce to me an application for vaccum tube design

[@UsagiElectric]

Hello! There are a ton of applications for vacuum tube designs! Personally, I'm absolutely fascinated with tubes being used in computing designs, which is why I'm slowly building up a 1-bit computer out of tubes. But tubes are really, really versatile and can be used in all sorts of wild applications like synths, analog computers, ADCs, test equipment, amplifiers, etc. Really, just about any electronics project can be replicated or done with tubes, it's just a question of how many tubes you want to use, haha.

[@amirrezasherkoshan169]

@@UsagiElectric hello sir So i want to use PFL200 and 6HG8 tubes but i didnt find any library for them

[@UsagiElectric]

@@amirrezasherkoshan169 The 6HG8 seems to be a triode pentode and the PFL200 is a dual pentode, which is very cool! Here's the datasheets: frank.pocnet.net/sheets/030/p/PFL200.pdf frank.pocnet.net/sheets/107/6/6HG8.pdf Also, check out Franks webpage, there are datasheets for just about every tube stored on there! frank.pocnet.net/ The triode pentode can be used to make some audio amplifiers. The pentode can actually be triode strapped to give some really nice linear response that works pretty well for audio setups. Check out this powerpoint on triode strapping: www.audiodesignguide.com/New2A3/ETF06TS.pdf The dual pentode can be used for a lot of different things, but I personally love building pentodes into logic circuits. The PFL200 would make a cool SR Flip Flop! There's a bunch of different ways to tackle building an SR Flip Flop, but check out IBM's customer engineering manual for how they build flip flops (that they call triggers) using a multivibrator: www.bitsavers.org/pdf/ibm/604/227-7609-0_604_CE_man_1958.pdf

[@richardhaas39]

@@UsagiElectric Crypto equipment also used tubes: heptodes.

[@nixietubes]

omg what is the music?? it sounds like a bastardized version of the chrono trigger soundtrack 4:53-4:58 is totally chrono trigger edit: oh you put the song titles in the video oop

[@UsagiElectric]

Yup! You were totally right, it was an excellent piano piece inspired by Chrono Trigger that I just love listening to!

[@CraigHollabaugh]

Excellent work, don't hurt your back lifting it around your shop. Here's a little 150A history, www.hpmemoryproject.org/news/150a/hp150a_page_00.htm

[@UsagiElectric]

You're not joking! Carrying this beast from the shop to the house and back made me realize just how out of shape I am, haha. That site is the one I came across when I first searching about the 150A with the absolutely amazing picture of the doors open and tray pulled out. HP had a penchant for really beautiful designs!

[@CraigHollabaugh]

@@UsagiElectric Yes, I hadn't seen a pull out tray like your 150's vertical amps before. I have a lot vintage test gear around here. My prize find was HP428B Clip-on DC Milliameter, not one but 2 in working condition. They're quite handy for biasing tube amp push-pull output tubes. Good luck with your latest acquisition.

[@UsagiElectric]

@@CraigHollabaugh Whoa, the 428B is an awesome little piece of equipment! I hadn't heard of that one before, but looking it up, man, a clip-on milliammeter would be so useful in so many situations! Plus, it's a really cool, almost hybrid, design using both tubes and transistors inside. What an awesome piece of equipment! Man, now I've gotta keep my out for one, haha.

[@dng88]

What is 5:45 doing ....

[@UsagiElectric]

At 5:45 I was cutting out the little board that converts the 6AN8 plug to fit the 6CG8. That was all done before I realized that the two tubes had a shared cathode... oops! The board I show at 10:35 is the one I was cutting out at that time.

[@dng88]

Usually capacitor (Mac SE) is the problem ... Pretend to watch the video live ...

[@UsagiElectric]

Whether the gear is vintage or modern, bad caps seems to be a common theme, haha. This one has a ton of "black beauty" caps that are going to need some replacing!

[@dng88]

always find it very fascinating ... but it is so big compared to you ... :-))).

[@UsagiElectric]

And I'm not a small person - I'm 6'4" or 195cm, so if it looks big next to me, that means it's really huge! I know I'm getting stronger by carrying this thing around though, haha.

[@MrRedwires]

I am so glad HackADay recommended this video, because it was a fantastic and comfortable watch, and it's really interesting! Good luck getting it to work, and I'll happily follow along :)

[@UsagiElectric]

Thank you! And thank you for letting me know that HackADay had an article on it, I was trying to figure out where the huge bump in views came from, haha. I've got some parts arriving today that should hopefully get this scope back up and going soon!

[@MrRedwires]

Lovely! This seems like such a pleasure to work with, especially with the construction that swivels open like this. They quite literally don't do it like that any more and it's such a shame, so this is a really nice refresh :)

[@seniorbeavis8954]

Your hair is out of control. You smile too much. Your new intro with the saxophone is irritating. Your logo looks like a butt crack. Your videos are twice as long as they need to be. Still love your stuff.