Inside a High-End Vintage Tektronix 7904 Oscilloscope, PCBs from 1968-1974 (unusual construction)

[@Quadraphonicsoul]

That hurt my soul to see these getting taken apart

[@Lantertronics]

I hadn't realized so many people still use these and love them so much. Y'all have convinced me to get them working again.

[@Lantertronics]

I need to figure out where to put them. They are HUGE.

[@ericrawson2909]

Hurt my soul too. I would lovingly restore them. If you don't have space you should advertise them so someone can look after them.

[@williamogilvie6909]

Very childish to just pull parts off at random and not put them back. You turned what was probably an excellent oscilloscope into scrap electronics. Someone should give your hands a few hard slaps with a ruler.

[@ScottyBrockway]

Those are beautiful, please give them to tektronix collectors/repairmen.

[@Lantertronics]

I wish I could; but they're Georgia Tech property and there's hence strict rules around them. They or any parts extracted need to either stay at Georgia Tech for Georgia Tech purposes, or they need to be officially surplused, meaning they wind up in warehouse someone in Nowhere, Georgia never to be seen again. None of my colleagues are interested in this stuff, so I'm their last hope to avoid the dustbin.

[@kevy1yt]

The loop of wire is a delay line to align timing.

[@Lantertronics]

Oh! That's very interesting!

[@kevy1yt]

@@Lantertronics yeah isn’t it? Back then that was a robust way to phase align signals. That’s why it’s a coax cable - to reduce external interference.

[@cheater00]

@@Lantertronics there's a Tek device used for pre-delay for i think the 500 series oscilloscopes (they're the older, tube based, modular tek scopes) that's basically a spool of hard coax in what I think is a 6U rack or something to that effect.

[@CraigHollabaugh]

I grew up with those Tek mainframes on the tilting cart. They were great teaching tools because there was no 'auto' button. Thanks for the memory stroll.

[@fullwaverecked]

Hey Craig, nice seeing you here. Love the vintage Tek.

[@John.Doe.2025]

Is that realy someone use the "Auto" button?

[@wellscampbell9858]

@Lantertronics, I’m about a month late so don’t know if you’ll see this, but thanks for the tour! I’m the proud owner of a Tek 485, which is a portable analog scope from the same time period, and one of their higher end units-I believe it’s rated to 350MHz. Got it a year ago on Craig’s-list, with a new set of probes, for $100! It worked, and with some switch cleaning and a simple calibration procedure to fix a trigger issue it functions perfectly from what I can tell. It’s a gorgeous dense block of fine analog electronics on the inside. I found a comprehensive repair manual with schematics and board layout diagrams, so I’d imagine similar materials are available for your units. The vertical amps in particular are supposed to be engineered to an amazing level of precision, and an interesting tidbit: there was a caution note saying that some of the transistors shouldn’t be disturbed, as part of factory calibration involved adjusting how they were seated in their sockets!! That blew me away... I learned that the round parts are tektronic custom ICs (another commenter noted this as well) and the jumpers with pin and sleeve contacts are coax. Glad to hear you’ve decided to attempt restoration, and good luck!

[@Lantertronics]

Right now my main restoration task is to just put all the parts back in the right places. ;)

[@skysemone6355]

I got a pretty large set of these from a local university for $20 when I started making DIY synths. I still use 'em all the time even though I have more modern equipment now.

[@stevesmyth4982]

The coil of blue wire is a delay line and the board mounted switches inside the Al cans are Y input attenuators.

[@Lantertronics]

Interesting!

[@Janktzoni]

You probably caused multiple heart attacks and mental breakdowns with just this one destruction video.

[@andywlala]

These are gorgeous scopes, find a way to make room to keep them - you seem like you respect good engineering, these still represent good electrical engineering, and are rewarding to get to know. You could do worse than find a way to teach some of the positive principles from these designs to your students, while also highlighting the total lack of design for manufacture (which is par for the course in that time, but an advancement that is well worth highlighting for today's students.) I believe Tek used to have their own fab line, because they designed and built their own custom chips (because they simply could not buy what they wanted on the open market) - I think they sold the fab to Maxim way back when, and of course, Maxim is now owned by Analog Devices. Also - it is worth learning how the readout circuits used in the 7000 series works, it was an absolutely fantastic design (by Barry Gilbert, he of The Gilbert Cell). Powerful, yet simple to implement - some of those boards above those cam switches were the readout boards for those modules.

[@Lantertronics]

I have been convinced to try restoring these.

[@andywlala]

@@Lantertronics Nice. From an EE perspective, they and HP gear of a similar vintage represent excellent designs that you can actually wrap your head around and teach/learn, instead of let's just throw a cpu at that. Much like the Buchla or Moog circuits you wrangle so well.

[@fletcherreder6091]

Roughly in order of appearance: The 0078's are high speed broad band amps. 0160 is a trigger amp, and next to it is 0150 a trigger detector.The 0185 is a 4 decade BCD counter. No luck on the TO package IC's, Fairchild I think. Same with the Raytheon, there's a tube with that number that dominates the results. 0035 is a wide band quad op amp. Blanked out one is probably a CotS replacement of a custom chip. 723hc is a voltage reference. Choice of sockets was often down to parasitics; more sensitive and higher speed stuff required lower profile sockets. 0049 is a sweep control, similar in spirit to a 555, nifty part. 0061s are more trigger amps. I think that's it for the odd stuff.

[@Lantertronics]

YOU ARE AMAZING!

[@sonovoxx]

Very interesting. I have a 7904 carcass along with some modules - it was my main oscilloscope until lockdown when it finally let out the smoke. I had fixed it numerous times previously, but needed something more reliable and portable, so it took it apart. I harboured the idea of using the thing to make like an API style lunchbox of custom audio FX... but I haven't even fixed all my normally broken kit, never mind something that needs lots of design attention! Great video - enjoyed trawling along with you there.

[@Lantertronics]

It's a beautiful unit, but yeah, it's soooo bulky...

[@sonovoxx]

@@Lantertronics it's deep man, too deep! Heavy too! Actually the thing that impressed me was that IF you can dig the main PSU filter caps out from the back end of it, they are incredible quality, and mine showed no increased ESR even after all these decades! ...also fun "Warning, 7000v!" type labels on the main carcass. ⚡👋

[@arthurharrison1345]

2:55 - The white adjustable component is a variable capacitor.

[@danielepatane3841]

these are the finest pieces of electronics built by tek back then. It is well worth to repair these as their specs have nothing to envy to actual oscilloscopes...good luck!

[@electrifyingvids3545]

DON'T TOSS THEM! They're still really good scopes! You can turn them into a spectrum analyzer, a multi meter, a regular scope, or even a curve tracer! These are modular, yes they take up a lot of space, but I find these main frames to be still more capable than most modern devices. If you have no choice but to get rid of them, put it up for auction or something, or give it to some one who cares about it, and will take care of it. I have a deep moral that says no Tek instrument should be thrown away.

[@Lantertronics]

Alas, they were inventoried Georgia Tech equipment; we're not allowed to sell them. I would have sold them or given away to someone who appreciated them if I could have. None of my colleagues were interested in them, and they think it's weird that I'm so interested in this "old stuff." Because of space, I wound up having to surplus the mainframes, but I kept the plug-in units for parts (I also have a bunch of 500 series plug-in equipment I'd like to build an old-fashioned pre-modern-synthesizer electronic music studio out of, like Hainbach and Stockhausen. Again, my fellow professor think I'm nuts for my interest in old equipment).

[@Lantertronics]

I've sorted the 500 series stuff into the categories of "turns on," "turns on but smells bad" (I think some tantalum caps have had tantrums), and "doesn't turn on." I'm hoping to interest some students into testing and calibrating them. I find students are fascinated by older technology, like this stuff and the S-100 bus computer systems we are playing with, because they can *see* things -- most modern electrical and computer engineering is so opaque, with chips with billions of transistors and piles of abstractions.

[@davidjh7]

In case nobody else mentions it, the multi-pin odd looking round IC's, are custom TEK hybrid modules--basically unobtanium for people trying to restore these scopes. TEK actually set up their own custom fab, when they decided they couldn't get the speeds they wanted without their own process. The 7904 as only bettered by the 7104--I thin it is still the fastest analog scope ever made. It had a micro-channel plate for the crt to enhance the light output at those fast sweep speeds.The story goes that TEK developed it for the AEC to use to capture the very fast events from nuclear bomb tests, and the AEC bought a lot of them, With the matching 1 GHz amp and horizontal sweep module, the 1980 price was $21,530, or about $76,000 in today's dollars. The 7904 wasn't that much less, but had a much larger available market. The7904 is still one of my favorite scope platforms, and I'm definitely keeping mine. :)

[@Lantertronics]

I've decided to try to get these working. :)

[@thomaswilhelm3384]

Allot of those parts are worth money and the PC boards have a high gold content.

[@Lantertronics]

That's a non-starter. These parts all belong to Georgia Tech; much to my frustration, we have no mechanism of selling older things to buy newer things. But, I've decided to try restoring them so they will live on.

[@HermanStehouwer]

I like those integrated transistor sockets. I also guess you now have a whole bunch of matched transistors for $stuff.

[@cheater00]

terrible idea - those transistors are hard to come by and are matched in weird ways; you can get matched transistors matched /in a way that you can use/ for cheaper than the time it takes you to dig them out of the mainframe

[@ArguZ72]

My kind of unboxing...

[@petegreenwood2793]

In Jim William's book "Analog Circuit Design, Art, Science and Personalities" there is a chapter written by John Addis, who did a lot of the design work on the vertical amplifier circuits used in this era of Tek 'scopes, which goes into some detail on the design concepts that were employed. Indeed, there is also a chapter by Barrie Gilbert, as well as many other analog design luminaries. It's a must-have book if you're interested in analog design, full of fascinating insights from some of the brightest design engineers of their time.

[@Superbonker-np6iz]

OMG instead of pulling parts left and right why not give it away to someone who would restore it ? Those machines are historically important!!!!

[@Lantertronics]

Alas, it's inventoried Georgia Tech equipment. There's no mechanism by which it can be sold or given away; it either stays at Tech or it gets stacked in a warehouse never to come out again.

[@Superbonker-np6iz]

@@Lantertronics I'm sorry but if there's a need there's a way. Please talk to someone who could help preserve these wonderful devices.

[@Lantertronics]

@@Superbonker-np6iz Oh, I'm going to try refurbishing them, people commenting here talked me into it. Alas I'm the only person at Tech that cares about this; my colleagues think I'm crazy for being obsessed with what they consider "obsolete" equipment.

[@Superbonker-np6iz]

@@Lantertronics Oh thanks God you are going to restore them. I just read more comments and realized you may already be in touch with people from Tektronix who can help. Anyway thank you and I can't wait to see you post updates once in a while. Thumbs up all the way.

[@Lantertronics]

@@Superbonker-np6iz Yeah -- some original folks on the design team for these units got in touch! I had NO IDEA there was still this much love for these old beasts. :)

[@przemyslawbrys]

prof. of electronics...?

[@cheater00]

Hey Aaron, definitely keep the 7904 - it's the highest end "workhorse" type. I run the Tektronix / HP discord and we even have people from Tektronix there, so if you run into any issues, we can help you out with the repair, with schematics (for your specific serial number if they're not available on BAMA or TekWiki), and with spiritual support. You can email me (find my email on the synth-diy list) and I'll direct you to the discord.

[@Lantertronics]

How well do the capacitors hold up? Am I in for a recapping nightmare?

[@cheater00]

@@Lantertronics often you only need to do very selective jobs. other people in the community can tell you more - hop on over to the discord or ask on the TekScopes mailing list

[@Lantertronics]

I have been convinced to try restoring these.

[@cheater00]

@@Lantertronics great stuff. Bear in mind restoring one of those goes a little further than just "common sensing" some of the circuits. For example, tantalums have for a while been under-rated (because people did not know yet how to rate them correct), and some other things need, eh, "special care". If you post on the TekScopes mailing list, you'll get heaps of helpful replies!

[@jameslewis8227]

Of course you don’t have a hoarding problem… That was hilarious! I bet anyone who ever worked in an Air Force PMEL shop from the 1970s-1990s would suffer some serious flashbacks watching this video.

[@justovision]

Take it apart first? Don't throw those away!

[@Lantertronics]

I'm now convinced to try to get these working, even though I don't really have room for them. I'm hoping that having multiple units so I can swap boards and parts for troubleshooting can make it easier.

[@justovision]

American Universities: "Just throw it away. We don't teach history." Also American Universities: "Just raise tuition again."

[@justovision]

@@Lantertronics That's great. That era of circuits is so interesting and most of it is unobtanium now.

[@azmrblack]

If anyone wants to see the design part of these, here's a video from Tektronix on how the boards are designed: kzbin.info/www/bejne/bajIi2OKg7eWq9k

[@Lantertronics]

It blows my mind what they were able to do without modern CAD tools!