12 amp 115v slow blow fuses for KPA 500

Discussion in 'Amateur Radio Amplifiers' started by KB4OIF, Jul 14, 2018.

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  1. WN1MB

    WN1MB Ham Member QRZ Page

    3AG is the size form factor:


    Most popular such fuses in the USA are Littelfuse and Bussman.

    Here's a Bussman cross-reference:


    Littlefuse info:


    Don't buy cheap, no-name/no-brand fuses. Sooner or later, you'll regret it. And the results won't be pretty. Mouser Electronics is your friend.

    Unless an extraordinary emergency, never substitute a higher value or use slow-blow when fast/normal blow are specified. Know that if you do, a fault in your electronic equipment could fry circuitry and faithfully protect the fuse -- the exact opposite of what is supposed to happen. Think "weak link."
  2. G3YRO

    G3YRO Ham Member QRZ Page

    So what size do you normally use in the USA these days . . . .

    1 and 1/4 inch . . . or 20mm ?

    Roger G3YRO
  3. WN1MB

    WN1MB Ham Member QRZ Page

    Argh! I meant Littelfuse in my previous post. Damn fingers just didn't want to type "littel" that way! heh.

    I'd have to venture a guess and say that the 3AG size are the most widely used in the USA for electronic equipment - based on my experience. Other statesiders may correct me if I'm wrong.
  4. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    Oops, sorry John, Lou, Dave! Mea culpa. I should know better.
    I skimmed the manual to find the holder size and contributed to bad Zed info.
    I try to not do that. No more distracted posting looking up info for OPs, I promise.

    W7UUU likes this.
  5. N4FZ

    N4FZ XML Subscriber QRZ Page

    I'm glad you have the correct fuse specs now John. I would call Elecraft and speak with the "tech" that gave you the wrong advice! You might just help the next person out, if they don't follow/read :eek: the KPA500 manual first.
  6. KA9JLM

    KA9JLM Ham Member QRZ Page

    Normally 1.25 unless they are for something made in China.
  7. AI3V

    AI3V Ham Member QRZ Page


    Unlike you guys, with the fuse in plug. :)

  8. AI3V

    AI3V Ham Member QRZ Page

    And when fast blow isn't fast enough, try a fuse made especially for protecting semiconductors.

    KD2ACO likes this.
  9. G3YRO

    G3YRO Ham Member QRZ Page

    Equipment always used to have 1.25 inch fuses over here too (your 3AG size) . . . but not for quite a long time.

    Since the 70s we have standardised on 20 mm glass fuses :


    These are different from the fuses that we have inside our Mains Plugs - they are ceramic and slightly bigger :


    Just looked at that table of different fuse sizes you have over there (2AG, 3AG, 4AG, etc) . . .

    Why on earth would you make so many slightly different fuse sizes? Many are so similar it would be bound to cause confusion!

    Roger G3YRO
    Last edited: Jul 19, 2018
  10. WN1MB

    WN1MB Ham Member QRZ Page

    My introduction to these was way back when dinosaurs roamed the countryside and a customer came into the shop with either a Marshall or Sound City head for repair. ;)

    I think they were called "F-type" fuses.

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