Assembling a Heathkit HW-99

Discussion in 'Homebrew and Kit Projects' started by N5OLA, Jul 31, 2019.

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  1. N5OLA

    N5OLA Ham Member QRZ Page

    On a related question, while querying Mouser and others to find these 50 pF N75 caps, I'm asked what is the wattage. This isn't on the caps or on the schematic. I have no clue where to find it.
     
  2. N7EKU

    N7EKU Ham Member QRZ Page

    Hi,

    It's for a transistor VFO run off 12V -- any value you buy will work since the voltage will not be that high, nor the power.

    Have fun cap hunting,


    Mark.
     
  3. N2EY

    N2EY Premium Subscriber QRZ Page

    I don't think you need to replace those capacitors unless they test bad.
     
  4. N7EKU

    N7EKU Ham Member QRZ Page

    The VFO inductor in this kit apparently with heating, drifts in value a lot in the positive directionl So he's following a correction plan someone came up with that employs some negative coefficient caps...
     
  5. N2EY

    N2EY Premium Subscriber QRZ Page

    Understood.

    But, IMHO, it would be better to build the thing first, and then, if the drift seems excessive, to seek out the fix.
     
    WN1MB likes this.
  6. W9GB

    W9GB Ham Member QRZ Page

    N75 : ±60 ppm/°C max. capacitance change from +25°C reading over temp. range of -25°C to +85°C
    ==
    Craigslist, eBay. ... these are 25 pF
    https://www.dubuque-forsale.com/OLD...25-pf-ceramic-disc-capacitors-N75-5-qty-5.php

    OR contact SP International in Burnaby, B.C. (majority of their products are SMT parts)
    http://s-pintl.com/wp-content/uploads/2017-Capacitor-Catalogue-June-2017.pdf

    SP International
    650 - 3711 North Fraser Way
    Burnaby, British Columbia, V5J 5J2
    Phone - 604-324-4811
    Fax - 604-324-3184
    E-Mail - info@s-pintl.com
    Web - www.s-pintl.com
     
  7. N7EKU

    N7EKU Ham Member QRZ Page

    For sure,

    And if the inductor is the problem, then fix that first.

    73,


    M
     
  8. KP4SX

    KP4SX XML Subscriber QRZ Page

    Caps generally aren't rated for wattage.
     
    N2EY likes this.
  9. N5OLA

    N5OLA Ham Member QRZ Page

    If anyone is still following this thread, I appreciate all of your "pre-flight" advice on the HW99.

    It's moving along. I checked all the resistor values (replaced a few) and got new electrolytic caps to replace these 30+ yr caps in the kit. The boards are all assembled, and now I'm running the initial multimeter tests and hitting some sour notes. It's hard to know where the culprit(s) could be, as the parts are so old. My soldering is pretty good, no bridges or cold solder joints.

    I'm posting these queries in the technical forum "Radio Circuits, Repair & Performance" if anyone wants to come visit. Thanks again for all of your invaluable suggestions.
     

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