Taking Apart a Vintage Oscilloscope

After getting a power supply and a multimeter, the next piece of gear a hacker would want to add to their bench is the oscilloscope. Nowadays, even the cheapest ones cost a few hundred dollars yet pack in the features. At the other end of the scale, if you can pony up close to a  million dollars, you can help yourself to an oscilloscope capable of 100 GHz bandwidth and 240 GS/s sampling rate. With that perspective, it becomes interesting to take a look at this video (embedded below), where [Jack Ganssle] shows us the Philco 7019 Junior Scope which was introduced way back in 1946. It seems the Philco 7019 model was an identical re-badged version of the Waterman Model S-10-A PocketScope.

[Jack] is familiar to all of us as an embedded systems engineer, but in this video he does a teardown of this vintage analog model. He starts off by walking us through the various controls, of which there are not a lot, in this “portable” instrument. At around the 3:40 mark in the video, he’ll make you wince as he uses a screwdriver and hammer combo to smash another ’40’s vintage CRT just so he can show us it’s innards — the electron beam source and the horizontal and vertical deflection plates. The circuit is about as bare-bones as it can get. Besides the CRT, there are just three vacuum tubes. One is the rectifier for the power supply, a second one is used for the vertical amplifier while the third one is the free running horizontal sweep oscillator. There is no triggering option — you just adjust the sweep frequency via a potentiometer as best you can. It does have internal, external and line frequency function selection, but it still requires manual adjustment of the sweep oscillator. There’s no blanking signal either, so the return sweep is always clearly visible. This is evident from the horizontal burn mark on the phosphor of the CRT after decades of use. It’s amusing to see that the vertical position could be adjusted by moving a magnet attached to the side cover.

The Oscilloscope Museum website hosts the Instruction Manual for this model, as well as a sales brochure which makes for very interesting reading after viewing [Jack]’s video.

Thanks, [Itay], for the tip.

26 thoughts on “Taking Apart a Vintage Oscilloscope

  1. lol @ PocketScope …

    Is that a Gun PocketScope in your pants or are you just happy to see me overdosing on Viagra.

    My first scope was a Hitachi V212, two channel 20MHz electrostatic deflection CRT oscilloscope. Definitely didn’t fit in a pocket.

  2. My first oscilloscope had maybe 100KHz response, ac coupled and neither triggered sweep nor dual channel. Cost me $5.00 at n amateur radio club auction about 1972. It was heavy, but a considerable amount was in the cabinet. It was useful to play with, I hot my money’s worth. Then I got the use of a Tek 317 and that was a real scope. I gave the $5.00 one to a friend, who took it home on the bus.

    But that tiny scope may be more useful than something bigger. It’s no worse, but provides the basics for an audio display or to display a transmitter or whatever. For just the scope tube, there’s les to strip than a more complicated scope.

    I always liked one scheme that John W Campbell wrote bout in CQ in the late fifties. If you reduce the voltage to the anode, you get a more sensitive deflection, albeit less bright, so you can run it without an amplifier, and the trouble of making it broadband. With cheap DVMs, one could use DC to compare AC deflection with DC, just needing some scheme for the sweep.

    Michael

        1. http://tubebooks.org/Books/rider_crt.pdf (page 59)

          If that fails to load go to the main site
          http://tubebooks.org/technical_books_online.htm

          scroll down to The Cathode-ray tube at Work, John F. Rider, 1935, 336 pages
          and click on Download full text with index, 17MB PDF file

          You can also find schematics on the net, just type in: “neon tube relaxation oscillator” or something similar.
          I’ll be watching this page for few more days, so if you run into trouble say so in the comments.

  3. My first scope was a Hartley 13A .. 2MHz bandwidth (which I doubt), but it did have dual traces. That was 1972 .. it was marked with Air Ministry branding from 1952. It was vaguely portable, but it was very heavy due to the oil-filled transformers it used. It was lost in a house move in 1982 ..

  4. my first oscilloscope was a TTM 303A, built in japan, still dont know the full name of it, i got it from a shipyard where they were used for 20+ years, i picked up the scope, a signal generator, dummy load and power supply for next to nothing.

    the scope is a rugged unit, no idea what bandwidth or specs were like but i still use it every now and again, there is an internal battery so it will run without mains, though it is about as “portable” as early cell phones.

      1. not really which was surprising, it was doa, i got all of it sight unseen from a friend i knew at the yard.
        the unused connectors on all of the equipment were corroded to the point where one had to clean them up to get a connection, spare connectors work great to wear in a contact pattern, if that fails there is always vinegar.

        this didn’t seem to do the trick so i had to open it up, the battery had dried out so i removed it, sill no dice, at that point i decided to short the battery connector on the assumption that the battery actually had some form of switching circuit that couldn’t work without a closed circuit, i was probably wrong, still didn’t work.

        with all of the easy fixes gone i did the boring thing and disassembled it looking for dead caps or obvious damage, found a couple of dead caps in both the power supply and crt section of the scope so i ordered parts and replaced them, cost me roughly 20 euros including the gel battery, that was ten years ago, it still works, even if the crt is getting fairly dim.

        the signal generator simply worked, as did the dummy load, the power supply died within a month and was generally horrible even while in use, i wore it out on electrolysis and salvaged it for parts.

  5. I was waiting to hear him say that the CRT he destroyed was already burnt out anyway. I did not hear him say that!

    Also cringe-worthy… even as he warned about it his fingers really seemed to like the area around all those exposed HV connections!

    Seeing how simple that schematic was… made me start to think about getting an old camcorder CRT and building one like it. I had to remind myself of all the more practical projects I also don’t have time for.

    Magnet… clever.

    So… should the ramp really be a true triangle wave? That assumes the CRT’s deflection is linear. Is it? I can’t imagine any good reason for the return not to be as fast as possible but maybe the roundedness of the ramp was intended to compensate for non-linear deflection in the CRT. I’ve never built anything using a CRT before so I wouldn’t know.

    Also, how much of that imperfection is due to the primitive nature of the device and how much is because it is 60 years old? Would a re-cap and tune up make it better? Not that a 700k oscilloscope would be worth that effort as a tool… but if you are in to restoring and collecting things…

    Why is the right side of the CRT not displaying anything? Is this just a knob he needs to turn? My much newer, 1990s CRT oscilloscope has such a knob. Or is it back to the fact that this is a 60 y/o scope and needs a re-capping and tune up?

    1. “I had to remind myself of all the more practical projects I also don’t have time for.” – LOL. I actually have a CRT ready, but so far I haven’t been able to get any sign of life out of it. It’s a Tek CRT tube from 1970 with lots of wires and no manual.

        1. Ok. Tube is dual beam from 1970. Tek scope. Numbers on the CRT paper label are: part no. 154-0636-00, made in USA, 38305, 24-2. I don’t know the scope model number. There are some numbers embossed into the metal on top of the scope tube: 522 F 41. Base has 20 pin tube socket. 7 (2+2+3) additional pinhole connections are at the scope neck. In addition to this, 7 pin ribbon cable leads to the point about 1/3 from the scope screen face, where something that looks a bit similar to a degaussing coil is wound around the tube.

          Heater is ok, it glows when 6.3 V is applied.

          1. It was used in Tek models 310/310A, 315, 360. They were manufactured from the early to mid 50’s till the early 70’s.

            You will find information and manuals/schematics in the site below by entering the model number into the search box at the top of the page –
            http://w140.com/tekwiki/wiki/360

            This tube is very rare you may consider selling it and buying a simpler tube if a rectangular tube is ok for you –
            http://www.sphere.bc.ca/
            The people that run the above site resell old stock and they may be very helpful with design as well.

          2. PS: You should check this information.

            This CRT in unconventional.

            The conventional arrangement for modern CRTs High Voltage (Anode) is to have a Flyback Transformer (LOPT) that drives a positive voltage though an anode lead to an anode cap.

            If the info I found is correct, your tube grounds the anode and drives one side of the cathode to -1,700 Volts to -2,000 Volts. Of course the voltage across the cathode is still 6.3 Volts.

          3. Thanks so much RÖB. I will check that info and maybe get the tube tested sometime next week on the low HT. If I’m unable to get it working maybe I’ll offer it on Ebay.

    2. Electrostatic deflection is proportional and linear. Old CRT screens had a curve to keep things linear. Newer CRTs were flat and the resulting non-linearity was ignored because it was not visibly significant.

      Most of the *problems* you see with this old are are from worn out components – dry capacitors – high resistors and dirty calibration pots.

      Half the width of the image is missing because of old parts.

  6. I built my first oscilloscope, it was about the same as the Philco above except that it was nearly 20 years later and thus much less primitive. The single valve timebase was the Miller-Transitron circuit which is worth looking up to see the cleverness of valve circuit designers.

  7. Philco was cheap.
    In ’69 I figured out how to turn a TV into a audio only scope, I was too cheap to spend $2.50 for those plans that were for sale in the zines.
    I am also thinking about a viewfinder CRT for a similar audio display, but this time it will be possible for it to be a pocket-scope.

  8. My first scope in 1964 was the Pocketscope – it looked just like this one! Must have picked it up at a flea market or something and got it working. I remember cleaning it up first due to a layer of dirt that had accumulated.

    This is a trip down memory lane. I eventually rebuilt the entire thing from scratch in a different enclosure and did many mods to “improve” it.

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