Heath SB 301 rebuild

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

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  1. K7OPA

    K7OPA Ham Member QRZ Page

    I need some help with my SB 301. The unit was modified in several locations and DOA when I got it. Without a lot of test equipment I have got it to receive on AM, but only hum on other modes. Long story short, I am in the process of rebuilding the IF board but the manual that came with it has confusing entries. In the parts list the caps are called out in pf but on the assembly pictorial they are labeled ufd. example parts list - .01pf, pictorial .01ufd??? 3 very small units, 1pf and 5pf - are they realy ufd?? Also a .2 ufd Mylar banded - is this an electrolytic?
    Thanks for any help. Ron
  2. W9GB

    W9GB Ham Member QRZ Page

    Rap on Capacitors
    Harvard University, NMR Lab, Charlestown Navy Yards

    Electronics Notes

    Popular capacitor conversions
    There are a few popular ways of writing capacitor values. Often for example a ceramic capacitor may be given as a value of 100nF. If used in circuits with electrolytic capacitors, it is often interesting to realise that this is 0.1µF. These useful conversions can help when designing, building, or maintaining circuits.

    100pF = 0.1nF
    1000pf = 1 nF
    100nF = 0.1µF
    Capacitor conversion nomenclature
    Although most modern circuits and component descriptions use the nomenclature of µF, nF and pF for detailing capacitor values, often older circuit diagrams, circuit descriptions and even the components themselves may use a host of non-standard abbreviations and it may not always be clear exactly what they mean.

    The main variations for the various capacitance sub-multiples are given below:
    • Micro-Farad, µF : The values for larger capacitors like electrolytic capacitors and even some paper capacitors measured in micro-Farads might have been designated in uF, mfd, MFD, MF or UF. All of these refer to the value measured in µF
    • Nano-Farad, nF: The terminology of nF or nano-Farads was not widely used before the standardisation of terminology, and therefore this submultiple did not have a variety of abbreviations. The term nanofarad has come into much greater use in recent years, although in some countries its use is not as widespread, with values being expressed in large numbers of picofarads, e.g. 1000pF for 1 nF, or fractions of a microfarad, e.g. 0.001µF, again for a nanofarad.
    • Pico-Farad, pF: Again a variety of abbreviations were used to indicate the value in picoFarads, pF. Terms used included: microromicroFarads, mmfd, MMFD, uff, µµF. All of these refer to values in pF.
    The standardisation of terminology has assisted in the conversion of values from one submultiple to the next. It has meant that there is considerably less room for misunderstanding. It is easier converting from µF to nF and pF.
    N2EY likes this.
  3. KK6IYM

    KK6IYM Ham Member QRZ Page

    I looked at my manual, and the parts list has both pf and ufd parts listed. I did not see the discrepancy you have stated.
  4. AD5HR

    AD5HR Ham Member QRZ Page

    The band on the .02 cap denotes the outer foil.
    Usually connected to the point nearest ground potential.
    .01 pF is such a tiny value as to be swamped by lead, and
    wire capacitance.
  5. K7OPA

    K7OPA Ham Member QRZ Page

    Thanks to all - good info but really doesn't answer my questions. I have searched everywhere but cannot find banded mylars - what is best replacement? And what is proper cap to use on the IF board - pf or ufd. Thanks
  6. K7OPA

    K7OPA Ham Member QRZ Page

    snaps from same manual, different page

    Attached Files:

  7. AD5HR

    AD5HR Ham Member QRZ Page

    21-14 & 21-16 are miss-prints, should read microfarads.
    The 1 and 5 pF are correct values.
  8. W7UUU

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

    It was exceedingly rare for Heath to have typos!! When you consider that a typo could easily lead to "failure to work", they worked extensively to prevent them. At one time (during the SB years) their manual production was practically a factory in itself, with dozens of copy writers, proof readers, drafters and artists, typists, etc. etc. - most kits had a dozen or more - in some cases as many as a hundred - kits taken home and built by employees to look for omissions, confusing drawings, missing instructions, and ... typos!

    It's so rare in fact that I've only ever seen a few, and there was an errata sheet in the manual to cover them.

    Just a factoid...

  9. K7OPA

    K7OPA Ham Member QRZ Page

    Thanks Jon! That was my assumption but you know what happens when you ASSUME something :)
    Any clue re the banded cap?
  10. AD5HR

    AD5HR Ham Member QRZ Page

    Well, if the pics. posted in reply #6 are from a Heath manual, I think it is a
    Have you ever seen a .001 pF disc cap? <grin>

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