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Heathkit Condenser Checker

Discussion in 'Troubleshooting and Repair' started by (*steve*), May 2, 2020.

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  1. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    It's a really nice warm sunny day, so what better to do than to sit outside and restore something old and electronic!

    This is what I'm going to be working on today:

    IMG_20200502_133850_compress2.jpg

    I have no idea how long it will take me (I guess it will be more than one afternoon) but I'm going to be posting in real time... because I can.

    As you can see, it's 110V, and I'm hoping the transformer allows me to rewire it for 220V.
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    It's hello together with a pair of what appear to be self tapping metal bolts.

    IMG_20200502_135011_compress34.jpg

    As you can see, the case is in pretty rough condition, but I don't base my purchases on looks. I go strictly on price!
     
    Last edited: May 2, 2020
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    First look inside:

    IMG_20200502_135936_compress88.jpg

    And underneath:

    IMG_20200502_135957_compress14.jpg

    It's a bit dusty, the transformer clearly has a single primary winding, and a couple of capacitors seen to have been replaced.

    Some of the soldering looks pretty rough, but it's probably mostly functional.

    The getters on the tubes are still nice and shiny.

    At the very least it's going to need a clean to get the spiders out (literally) and I think the switches and pots deserve a good clean before I think about powering it up.
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Here is an example of one of those solder joints

    IMG_20200502_141938_compress15.jpg
     
  5. bertus

    bertus Moderator

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  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Here are two capacitors, both 8uF, similar voltage rating, and old. However, I'd the smaller one a replacement?

    IMG_20200502_143036_compress44.jpg

    And that's no way to treat a radial capacitor!

    IMG_20200502_143114_compress54.jpg
     
  7. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Thanks for the links @bertus.
     
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Well, it kinda works.

    It is close, but by no means accurate in it's capacitance measurements.

    The leakage test function delivers half or less of the expected voltages, and on the highest voltage range detects a good cap as leaky.

    I strongly suspect that some of the older capacitors are leaky, and the power supply filter caps are probably pulling the voltages down.

    I'm going to compare some voltages from the circuit diagram and see what I can see.

    Oh, and yes, I checked the heater voltages to make sure that someone hadn't slipped in a 220V transformer. I was getting the expected voltages there.

    IMG_20200502_155356_compress8.jpg
     
  9. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Voltages are all over the place.

    IMG_20200502_160347_compress90.jpg

    The 458VAC from the transformer is within spec, but I had to double check what I was reading when I measured the +150V rail. This started closer to 300V and then dropped, and continued to drop as long as I measured it.

    The -410V rail is also low, measuring -245V, but the sun of the two voltages (435V) is less dramatically different to what I would expect (560V).

    My guess is that the big old capacitor is very leaky.

    The plate voltage on the 1629 is also high, but that is pretty much expected given the higher supply voltage. It also probably explains why the magic eye tube was so easily visible outside in daylight!

    I'm going to replace some caps and check some resistors, but it's probably time to go inside shortly...
     
  10. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    The resistor values are mostly remarkably within tolerance. One has gone high, one is currently across a capacitor, and the last one can't be located!

    Many of the resistors (10%) are well within 1%!

    IMG_20200502_163025_compress69.jpg
     
  11. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Ok, so the sun has set, but before it did I replaced those two electrolytics.

    I also touched up most of the solder joints and measured the resistor across the filter capacitor. That resistor had gone a little high, and that may be part of the reason for the higher than expected V+. I may replace that later.

    IMG_20200502_181220_compress35.jpg

    I hope I got them around the right way :). Both 500V 10uF.
     
  12. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    ...and those 2 replacement caps did the trick.

    The +150V now reads +167V, and the -410V is -407V.

    With the voltages correct, the capacitance readings are closer, but if the calibration routine doesn't fix it I'll probably have to replace the reference capacitor with something a little more accurate. The pot also seems a little noisy, so that might be worth replacing too.

    The leakage test works on all ranges with a known good capacitor, although the voltages are low. I get:

    25V range: 34V
    150V range: 108V
    250V range 189V
    350V range: 267V
    450V range: 382V

    Apparently those voltages are about right (after some googling). I'll pull out some precision resistors tomorrow to check the accuracy on the resistance ranges.
     
  13. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Random thoughts...

    1) One valve is being used as just a diode. Could I replace that with a bridge rectifier? (Or even just a a semiconductor diode?) I think it might stuff up the voltage regulation though.

    2) Convert to 240V operation by adding a small auto-transformer.

    3) Remove the line cord and replace with an IEC socket and ground the chassis.
     
  14. bertus

    bertus Moderator

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  15. duke37

    duke37

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    I would go for all three of your suggestions. Removing the 1626 triode will give plenty of room for an auto transformer. The power will be fairly low as no heater power is required for the rectifier. Perhaps the triode was chosen to give low voltage drop, it being intended to be used for power pulses.
     
  16. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    First thing to look at is the accuracy.

    I have standard resistors between 1Ω and 1MΩ (in decades). These are well within 0.1% tolerance (the 1kΩ was read as 999.96Ω) and plug in directly to the measurement terminals.

    IMG_20200503_133008_compress73.jpg

    Using the alignment procedure I aligned it for 1kΩ (they specify 2kΩ) and then checked the same range with 100Ω and 10kΩ. Both of these are significantly out. Switching to the Rx100 range, it was pretty accurate on the 100kΩ resistor, but significantly out on the 10KΩ and 1MΩ.

    It looks a bit like someone has replaced the potentiometer, and it may be a different value than the original. I think I'll order precision resistors and a replacement pot -- they won't be to expensive. I will check the switch contacts again, because these might be another source of trouble (I should do that first).

    On the capacitance range it's also way out on the higher ranges. I think the replacement of the original 2uF non-polarised paper cap with a 2uF electrolytic (by some previous person) was not the best option. I had always intended replacing this anyway, so it's just one more thing to replace.

    On the lower range it's also inaccurate, but in a manner similar to the resistance ranges, so I suspect the resistive division ratio needs to be fixed before I can see if there's something to fix here. I'll probably order some replacement caps anyway, as they won't be hugely expensive.

    Oh, and those old terminal posts are pretty beat up and someone has hit one with a hammer (or dropped the unit) so I'll try to find some that look similar and replace them.

    I did use this device to test the leakage on the two high voltage capacitors I removed. Sure enough, the large cardboard (original) one has several mA of leakage; enough to load down the test voltage considerably. The newer (Sprague) one has only hundreds of mA leakage at around 350V, so it's probably acceptable good. I used my leakage adapter to measure the actual currents and voltages, but the magic eye is a pretty good indication.

    IMG_20200307_163443_compress68.jpg
     
  17. WHONOES

    WHONOES

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    Looks like an axial cap' to me.
     
  18. Bluejets

    Bluejets

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    There are the elcheapos but Hirschmann make decent ones for around $7 a piece ...RSComponents
     
  19. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Here is a better angle

    IMG_20200504_122421_compress94.jpg

    It might be axial now, but that's not how it started its life.
     
    bertus and Bluejets like this.
  20. bertus

    bertus Moderator

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