Heath SB 301 rebuild

Discussion in '"Boat Anchor" & Classic Equipment' started by K7OPA, May 7, 2019.

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  1. W7UUU

    W7UUU Principal Moderator Lifetime Member 133 Administrator Volunteer Moderator Platinum Subscriber Life Member QRZ Page

    I didn't say it WASN'T. I was merely pointing out that typos in Heathkit manuals are exceedingly rare. And you found one! :)

    Dave
    W7UUU
     
    AD5HR likes this.
  2. AD5HR

    AD5HR Ham Member QRZ Page

    The .2 uF is not an electrolytic, and any Mylar .2uF at the correct voltage should
    work, it just may label the outer foil differently, or not mark it at all.
    W7UUU has much, much more experience with Heathkits, as well as many
    more on this site.
    Jon
     
  3. AD5HR

    AD5HR Ham Member QRZ Page

    Have to give credit to K7OPA, I was just the proofreader.
    First miss-print I've seen without a correction on the errata page,
    maybe it's missing from his?
    Jon
     
  4. W7UUU

    W7UUU Principal Moderator Lifetime Member 133 Administrator Volunteer Moderator Platinum Subscriber Life Member QRZ Page

    That's my guess. I can't imagine Heath letting a typo like that slip by - think of all the support calls!! Pretty sure the moment a typo was reported an errata sheet was added to the current stock of printed manuals, and immediately mailed to every owner. Especially on a high-end device like an SB-301. And of course, the moment the old stock of "has typo" manuals were exhausted the new printing would be the one they'd send.

    NOTHING like the so-called assembly manuals for those little kits from China we can buy on eBay :D:D

    I'll check my own SB-301 manuals later today when I'm home.... just see what I find

    Dave
    W7UUU
     
    AD5HR likes this.
  5. KK6IYM

    KK6IYM Ham Member QRZ Page

    Any of the caps listed in pf can be replaced with silver mica type. They will meet or exceed the component requirements of the Heathkit capacitors.
     
    W7UUU likes this.
  6. K7OPA

    K7OPA Ham Member QRZ Page

    Thanks all - just my luck to get one of the few manuals with typos! :)
    On top of that the previous owner made several changes that do penciled into the schematic, which I am trying to return to stock - oh well, I'm retired!
    Dave - I noticed in pics on another thread re sb301 you have installed a large cap at the .2 mylar location - what did you use? Thanks
     
  7. W7UUU

    W7UUU Principal Moderator Lifetime Member 133 Administrator Volunteer Moderator Platinum Subscriber Life Member QRZ Page

    Now you’re really taxing my memory LOL! I’ll lift the lid this evening and take a peek. I did that restoration almost 2 years ago

    Dave
    W7UUU
     
  8. W7UUU

    W7UUU Principal Moderator Lifetime Member 133 Administrator Volunteer Moderator Platinum Subscriber Life Member QRZ Page

    Well, I checked the three SB-301 manuals I have (why I have three I don't know...) but ALL of them are corrected versions. Your manual most surely was a very early release, before the typo was caught. Probably the very first batch that went out...

    Didn't get a chance to see what type of cap I used for the .2 but maybe this evening

    Dave
    W7UUU
     
  9. K9STH

    K9STH Ham Member QRZ Page

    Several things:

    First of all, any of the modern "poly" types of capacitors will work fine in place of the mylar capacitors.

    You really don't have to worry about the "outside foil" (which the "band" indicates) that were on the paper type capacitors when replacing the paper type with modern capacitors.

    "Orange Drop" capacitors, these days, are no better than the yellow or brown "poly" types and the "Orange Drop" capacitors are often several times as expensive as the others.

    You are not, generally, going to find capacitors with the "exact" values of the older types. Capacitors now follow the "tolerance" steps just like resistors. There are the "1" values (1 pf, 10 pf, 0.001 mfd, 0.01 mfd, etc.) but, instead of a "2" you will now find a "2.2", instead of a "3" you will find a "3.3", instead of a "5" you will find a "4.7", and so forth. The tolerances of most capacitors, and the paper types / electrolytic types were the worst of the lot, were not all that close and a "modern" capacitor will quite often be closer to the design value even though, to the decimal value, the value is not "spot on".

    Paper type capacitors were often +/- 30% and electrolytic capacitors were -50% / +80%.

    In equipment like the SB-301 (and I do have one), dipped mica capacitors can replace the old silver-mica (if used) capacitors and, if used as a bypass capacitor or coupling capacitor, a plain old disc ceramic will work fine. Years ago, small value capacitors generally had to be silver-mica whereas nowadays disc ceramic capacitors are available in the same small value ranges. You definitely have to be very careful where silver-mica capacitors are concerned because, as the age of the capacitor increases, the chances of "silver-mica disease" also increases and silver-mica capacitors are starting to fail on a regular basis.

    Glen, K9STH
     
  10. K7OPA

    K7OPA Ham Member QRZ Page

    Thanks Glen - great info.
     

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