National Model NC-33

Discussion in 'Wireless & RF Design' started by weirdwilbur, Mar 19, 2015.

  1. weirdwilbur

    Thread Starter New Member

    Sep 27, 2013
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    It has been in an attic box, with schematic, for 30+ years. Sometime cold, but very low humidity. Right or wrong, we turned it on, heard very faint voices and immediately shut it off.
    I suspect that there are right and wrong ways to properly resuscitate this guy, but I don't know your protocols. Are there any? I think I should asses each component before assuming it will not self destruct for want of a deteriorated part. Or maybe I'm being too wimpy.
    I need the benefit of your experience if you have the time.
     
  2. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    Where were the voices coming from? :)
     
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  3. DickCappels

    Moderator

    Aug 21, 2008
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    The thing most likely to give you a problem with receivers that have not been turned on for many years is that the electrolytic capacitors will have to be reformed. You can merely turn the receiver on and use it, but it might be better to reform the capacitors in such a way as to not let them over-hear.

    Turn on the receiver and only run it for a few minutes, then unplug it from the wall and feel the outer case of the large electrolytic capacitors in the power supply. If they are very hot to the touch, let them cool down, then run the receiver a little longer and repeat the procedure until the capacitors don't become very hot.

    The capacitors to worry about most are the 40 uf capacitors on either side of the power supply choke.

    [​IMG]


    The manual and schematics are at the URL below.
    http://bama.edebris.com/manuals/national/nc33/
     
  4. BR-549

    Well-Known Member

    Sep 22, 2013
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    Inspect the power cord. They get old and cracklely.
    And depending on your line voltage.....you might consider a polarized plug for safety, and a ground for better reception.
     
  5. alfacliff

    Well-Known Member

    Dec 13, 2013
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    the nc33 is a transformerless radio, one side of the line is connected to the cabinet.
    I sould change all the electrolytic caps because they are so old and they will fail soon. also, check all the waxed paper caps for leakage, those could take out tubes wich are getting rare. unless you have instructions and experience along with the proper test equipment, dont try to align the radio, please.
     
  6. weirdwilbur

    Thread Starter New Member

    Sep 27, 2013
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    Some of us thought maybe the umbrella stand. We didn't let it run long enough to hear identification for fear of frying the machine. They were speaking English and low volume. Yep, I tried the volume control. Remained weak. (The voices.)
    Do you think this machine can transmit?
     
  7. weirdwilbur

    Thread Starter New Member

    Sep 27, 2013
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  8. weirdwilbur

    Thread Starter New Member

    Sep 27, 2013
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    OK, got it. The direction to the paper work is a great thing. Thank you.
     
  9. weirdwilbur

    Thread Starter New Member

    Sep 27, 2013
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    Very good. Had not given it a thought. Does the ground attach to the case?
     
  10. alfacliff

    Well-Known Member

    Dec 13, 2013
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    do not connect a ground directly to the case, it is a transformer less radio, meaning one side of the ac line is common to the case. it is safer to use a 35 watt (or more) isolation transformer when using or operating these radios. a ot of these radio types had a "transmit" switch, they had no transmitter, the switch put the radio in standby when using an external transmitter. a lot of novices got their start with these radios.
     
  11. BR-549

    Well-Known Member

    Sep 22, 2013
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    "the nc33 is a transformerless radio, one side of the line is connected to the cabinet."

    I don't think that's right. Assuming the rig has not been modified.

    The circuit ground is the line voltage neutral IF the power plug is the right polarity.

    The circuit ground and the cabinet are only connected thru bypass caps.

    There should be NO continuity between either power plug prong and cabinet. If there is, there is a bypass cap shorted.

    The cabinet will have continuity with the ground at the antenna connection.

    If you use a single wire antenna.....you will have to connect separate ground.

    If you install a 3 prong polarized grounded plug in the proper way....a separate ground will not be needed. The antenna will be able to use house ground.

    These are great receivers. But they are not modern and you have to understand them to operate with good results. Otherwise you might mistake it for a boat anchor.

    From your questions, I suggest that you do no work on this unit.

    If you make a mistake....you and others might pay for it.

    Put this in the closet and learn on 12 volt stuff. This unit is not to learn on.

    What makes it leery for you is the fact that it has no transformer.
    This is dangerous.
    You have much to learn before you can safely work on it.

    I suggest "Electronic Communication" Shrader--second edition at amazon and others...~ $30. For anyone who likes old radios.

    These old rigs are great fun.
     
  12. alfacliff

    Well-Known Member

    Dec 13, 2013
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    asnd the caps from the ground wire to the chasis will conduct current. ther is no power transformer in the radio to isolate the line. just google the nc33 and you will find a lot of peopole that have rebuilt those radios, along with all the servce manuals and such. search on "boatanchors" for th BAMA site, lots of manuals there. due to the capccitors connected from each side of the line to the chasis, the chasis will be at about 60 volts ac no mater which way you plug it in. get an isolation transformer of 35 va or larger.
     
  13. weirdwilbur

    Thread Starter New Member

    Sep 27, 2013
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    You guys have been great. Just what I needed. Thank you very much for the needed encouragement and cautions. Is there a parts house that most folks like? Ann says that I have to buy a fire extinguisher first.
     
  14. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    I love National radios. I still NEED an NC-300 or 303....definitely on my bucket list! I do have a quite rare NC-109, which has a great xtal phasing circuit. Alas, it doesn't have the weighted National dial though. *sigh*
     
  15. weirdwilbur

    Thread Starter New Member

    Sep 27, 2013
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    I'm thinking that BR-549 has the best course for the likes of me. As electricity is witchcraft, I'm content to keep my distance from this project until a rational path presents itself.
     
  16. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    Yeah, the NC-33 was a "widomaker" design....forgot about that. While often advertised as being an AC/DC set, the topology was actually designed to bypass an expensive power transformer.
     
  17. weirdwilbur

    Thread Starter New Member

    Sep 27, 2013
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    We removed the case, before we plugged it in, and found it dust and spider-free. And oddly empty. You could put your lunch in there. We surmised that the main function was to accommodate the diameter of the tuning dials. As 1950's machines go, this box is light for it's size. So, if a guy was to actually get it working, should I add a transformer?
     
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