Tektronix 575 Mod 122C Curve Tracer Restoration Project – Part 1

A while back I picked up a Tektronix 575 Mod 122C transistor curve tracer from Craigslist and just started digging into it. With some encouragement from reader petepdx, I’ve started actually looking into fixing it up. (Click the photos for a much larger view!)

Inside, there’s some pitting and build-up, and some mildew visible around the CRT socket. There’s also a good bit of detritus floating around, from what looks like an insulator or spacer near the base of the CRT which disintegrated.

Nearly every tube was cracked in the socket. This must have taken a heck of a beating at some point. Dropped, maybe?

Using a shop-vac with a miniature brush, most of the dust and grime and bits of gasket cleaned right up. It’s actually not in as bad of a condition as it seems initially, at least cosmetically.

This doesn’t look great, though:

I do have a spare CRT for this unit, which seems to be in good shape. I haven’t pulled this CRT to see if it’s damaged.

There was a bit of dust, and white whispy build-up which could have been mildew on the paper insulation of most of the transformers.

Lots of surface corrosion in random places, too.

The inside of the Collector Sweep power supply doesn’t look too bad, though…but there’s that white discoloration on the main collector sweep power transformer still. Up top, not too bad. petepdx noted there should be a spool of silver solder inside – which there is!

It is desirable that only silver bearing solder be used on the ceramic terminals and for tinning the iron. Ordinary tin-lead solder may be used but repeated use will break the solder-to-ceramic bond. See your instruction manual.

Big power supplies on the bottom.

Lots of surface rust on one side of the main power transformer. On the panel-mount rectifier diodes, too.

Up top, there’s the horizontal and vertical drive circuits and the step generator circuits.

Finally, underneath is the CRT anode power supply, among other things. Some more white build-up here.

I also have a handful of the front panel switches, a full set of good pulled tubes, and a CRT from a 575 standard variant if I need them for spares. Overall, this is a bit of an oddball. There’s the mildew on the transformers, some mildew around the CRT, some evidence of water damage in the corners…the fuse holder is missing its cap, and was full of mud, and there’s some corrosion on the bottom deck neon bulbs. Otherwise, though, it’s actually surprisingly clean.

I’ll be going through it with a damp cloth shortly to remove even more grime and dust, and will post some photos of that step, then start looking into component replacements.

Possible plan for the resto:

  1. Thorough cleaning of grime and dust, oil fan bearings, clean/replace filter.
  2. Check and replace carbon comp resistors as needed.
  3. Replace tubular capacitors. Counted 18, may be some more hiding in there somewhere.
  4. Replace neon bulbs which appear in several circuit locations.
  5. Evaluate and replace as needed panel mount and ceramic terminal strip silicon diodes.
  6. Evaluate replacing HV power supply rectifier tubes with silicon diodes.
  7. Replace electrolytic capacitors. Quite a few of those.
  8. Visually inspect CRT.
  9. Test and replace tubes.
  10. Power it up with a Variac and hope nothing catches on fire.

It’ll be a big job to give it a full overhaul, hopefully nothing is too badly damaged which would make it impossible…

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16 Responses to Tektronix 575 Mod 122C Curve Tracer Restoration Project – Part 1

  1. Pete Lancashire says:

    Now more then ever convinced it came out of a shed/garage in the Pacific NW. And at one time experienced a big drop in temperature, hence all the cracked tubes. How about a real close photo of the white ‘stuff’ on the transformers. Another check is to make yourself a culture dish. sugar water + gelatin + light. And see if the stuff grows. For anyone that does not understand, the PNW is one of the most amazing areas outside of a jungle for growing microscopic ‘things’.

    • jwk says:

      You are almost certainly right, I did pick this one up locally, and I can’t imagine it’s traveled all that far in its lifetime.

      I’m intending to pick up this again as I’ve found some more time between paid shop projects and we’ll see what I come up with. Next will be checking resistors and such. Can you refresh my memory, which ones are the “glassohm” you were talking about? Are those the black, or the red, bodies?

      • petepdx says:

        “Glassohms” are light tan color, rectangular ‘wafers’. The cover is rubber. There is a 50 ohm one in picture DSC_0523. P/N 310-352. The substrate is glass, think something like a microscope slide. Don’t know who came up with the slang name, but it was in use when I started at Tek in the late 70’s.

  2. Poh Sin Hee says:

    HI i like to purchase this tektronix 575 from u with the crt intake. are u selling.

  3. petepdx says:

    Not sure if my last entry made it

    Looks like the neon bulbs are standard nothing special .. replace them !

    • jwk says:

      I approved it, it got stuck in spam for some reason! Also sent you an email privately as requested!

      I did discover the NE-23 is an NE-2 with a radioactive substance added to reduce the dark effect. The active source will have long-since decayed by now…maybe worth adding a couple of LEDs near the neons to provide some light? Or just not worry about it at all?

  4. petepdx says:

    Neons. look like you found they were all common, go for it.

    Ge power transistor, glad you have a spare. One thing to think about is to remount and replace the thermal grease on all the TO-36 TO-3’s.

    HV .. go with diodes, there been a lot of discussion on the two Yahoo Tektronix groups mostly centered around the 547.

    Ever go to Puyallup ham fair ?

    -pete

  5. petepdx says:

    The manual for the 575 was and still is a classic.

    It looks like the neons are standard, yes change them. Contact me if you need some more of the silver solder.

    On the HV there are some good comments on the Yahoo Tektronix groups. Most center around the 547. For me if I get to using my 575 again, I’ll swap them out.

    Ge with a stud. The die is mounted on the stud. it was an attempt at better heat dissipation.

    This maybe of interest

    http://powersupply.blogs.keysight.com/2012/08/early-power-transistor-evolution-part-1.html

  6. petepdx says:

    The CRT pots in the HV chain, intensity, focus, a-stig dont look good, fingers crossed.

    The CRT mounting

    DCS 471 .. yep, been in water, or sitting on something very wet.

    DCS 509 .. Pull the CRT, do what you can, if the CRT pin base is falling apart, let me know, it was pretty standard, and can get one of a reject CRT. Easy but time consuming to replace, you need a good solder extractor. I think there is suppose to be a foam like
    material around the clamp. Any modern high temp stuff will do.

    DCS 530 To the right is a glass-ohm. The initials in the box are from the person who built this unit.

    Tek was totally against the concept of a production line. Each instrument was completely assembled by one person. Sometimes an assembler would do extra work by pre-assembling things that were bottle necks but that was not the norm. It cost a lot more
    to do it this way, but the end quality was higher due to the pride one had. And at that
    time there was a lot of pride in saying “I built this”.

    Bringing the thing up .. phew. The long way is to put the thing on a Variac (or equiv) take about a week. I don’t see a thermal relay so HV will come up with the AC line. Don’t leave it by it self. The power transformer can short out long before getting to 115V. Put a 100W lamp in series. with the AC line. If the transformer does not short out, remove the 100W bulb.

    Replacing the power supply electrolytics is a crap shoot, if you take your time they
    may reform.

    Once you hit around 90-100VAC leave it on say for 5 minutes, turn off and feel the power transformer, then 10 minutes, 20, 30 … Do you have a AC line amp or watt meter ? They are great to have, specially if you have one with a settable trip.

    Get to 90-100V .. see what you have for HV. with tubes for the rectifiers their filaments have to be lit first, if you swap in Si diodes watch the HV as you bring up the line from 0
    If you get HV, turn out the lights, start looking for snap-crackle-pop and corona.

    Got HV and no trace, disconnect the deflection plates, put some insulation over the wires so they don’t short, try again. Work on HV first.

    There’s a good start.

  7. petepdx says:

    4. Replace neon bulbs which appear in several circuit locations.

    I would not change them right now. Tek used some special lamps with unique firing and other specs.

    6. Evaluate replacing HV power supply rectifier tubes with silicon diodes.

    Good idea. Today they are all basic in meeting voltage and current needs. Just check schmatics to make sure the design was not dependent on some spec. Are the all Silicon or are some Ge ?

    HV Transfomer

    Does not look like a sealed one. This can be good and bad. Good in that it looks non-potted, so no potting compound to absorb water (547 saga), Bad in that it looks non-potted, as water vapor can get it.

    If is bad or goes bad and your not trying to restore back to original there are plenty
    of HV ‘bricks’.

    That leads to my next guess

    My guess this guy has been stored outside in a barn, shed etc. The tubes maybe
    broken from extreme temp changes. I don’t think it is from a big shock, usually one
    would see bent aluminum around the power transformer.

    Talking about transformers Once you get this thing all cleaned etc, heat it up and dry it out. When I lived in Philly that would mean a house with oil heat and no humidifier 🙂 There has been a lot of slow oxidation.

    Just a big cardboard box and a source of heat.

    This is a good time to look for poor workmanship. It even existed at Tek, and it at times was from the intense schedules where orders kept out pacing production.

    On picture DSC_0547.JPG check the yellow/green wire where it goes onto the strip. I can see where the insulation is pulled back.

    DSC_0538. Upper left. At some point the condensation got so bad or this thing was
    sitting in dirty water.

    By theory about temp swings and the tubes, check the glass-ohms

    • jwk says:

      Awesome. Thanks for this detailed write-up. I found that the calibration manual does even list resistance-to-ground from test points, so I can use that to check out some of the circuit before getting started too much. I’ll be posting about this as I go along.

      I’ve had this one in climate-controlled, not-very-humid storage for about 1.5 years now, fortunately it’s not like it was just freshly removed from moisture or anything!

      For the HV diodes, replacing the 5642 rectifier tubes I was thinking the 3 x R5000F. Each is 5000 PIV, 200 mA, 500 ns recovery time. Looks like the tube is 10K PIV, and only 250 uA max current. The tubes don’t draw much, though, any reason I shouldn’t keep them?

      Service manual says diodes all are silicion per the service manual… looks like there’s some 1N647 (sub with 1N5407 now), two “silicon low leakage” diodes with “0.25w, 40v” (probably a 1N4148 now), 1N3209 panel mount rectifiers (still in modern production), 1N2862 (sub with 1N4007 now), and 1N3194 (sub with 1N4007).

      Germanium power transistors, though. I have one set of spares, from the donor I gutted, but those look tough to find. One is that weird pre-TO-3 package with a central mounting bolt.

    • jwk says:

      Are you sure about the neons? The ones on the bottom look pretty crusty, and I see NE-2 bulbs failing all the time in equipment that’s 20-30 years younger than this…according to the service manual they’re all NE-23 bulbs, which I imagine I can find “around”. I’m concerned that, since they’re often used as voltage regulators, firing it up with bad neon bulbs might damage something.

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