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    AO-10 Recap question

    I've successfully replaced the can capacitors with discrete caps in my B2's AO-10. Which other ones in the amp are electrolytics that should be replaced? I understand that replacing C2 and C11 will eliminate the thump when switching the vibrato tabs, but I am not sure if they are electrolytics, since the schematic doesn't seem to indicate one way or the other for any of the caps.
    Hammond L-102 "mobilized", Hammond M-3, Hammond M-101, Hammond T-211, Hohner Cembalet CF, Hohner Cembalet N, Hohner Favor Combo, Hohner Pianet L, Hohner Pianet T, Hohner Symphonic 30N, Leslie "430" (former 130 with horns and light show added), Nord Electro 3, and an entire village of guitars and harmonicas.

    #2
    All capacitors in the AO-10 1.0uF and under have paper, ceramic, or mica dielectrics -- as is generally the case for most electronics from that era. C2 and C11 are both originally paper, hermetically sealed in metal tubes. Part of me is thinking that you should know all that before attempting repairs on vintage tube electronics, but at least you're asking.

    It is pretty much unheard-of, then or now, to find electrolytic capacitors in 0.01uF or 0.0035uF values. Electrolytic capacitors were only ever used for one reason: to get a lot of capacitance in a small package.

    More broadly, in other amps, you do find electrolytics commonly used down to 1uF, sometimes even 0.47uF, but very rarely less than that, unless we're getting into miniaturized surface-mount stuff.



    I'm David. 'Dave' is someone else's name.

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      #3
      I suppose a better question would have been why do these capacitors look like electrolytics when their values are way to small to be electrolytics? That's good to know about their being sealed in metal tubes. So any film or paper capacitor would do the trick for C2 and C11?
      Hammond L-102 "mobilized", Hammond M-3, Hammond M-101, Hammond T-211, Hohner Cembalet CF, Hohner Cembalet N, Hohner Favor Combo, Hohner Pianet L, Hohner Pianet T, Hohner Symphonic 30N, Leslie "430" (former 130 with horns and light show added), Nord Electro 3, and an entire village of guitars and harmonicas.

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        #4
        Originally posted by theseacowexists View Post
        I suppose a better question would have been why do these capacitors look like electrolytics when their values are way to small to be electrolytics?
        Because before the Japanese got involved after the war, no one was the least bit concerned about miniaturization. Huge chassis had all the room in the world. A TV was rare and an AM radio was a living room console item. Bigger was always better in absolutely everything.
        Anything "small" was "cheap". So why bother with flux density? Wind some adding machine tape like a cigarette and shove it in a tube. Wave the flag. Eat a steak. All was good.
        When the Japanese showed they could put an AM radio in your *pocket*, the domestic manufacturers sputtered awake from their stupor and got in the game leading to what we have today.
        Okay, part of that is no domestic manufacturers -- having been regulated out of business -- BUT the technology is now alive and well.

        Comment


          #5
          Originally posted by theseacowexists View Post
          I suppose a better question would have been why do these capacitors look like electrolytics when their values are way to small to be electrolytics? That's good to know about their being sealed in metal tubes. So any film or paper capacitor would do the trick for C2 and C11?
          These capacitors don't really "look like electrolytics" if you have the experience with electronics to know the difference. It's kind of like I said above; no one at the time with any training in servicing electronics would expect a 0.01uf or a 0.0035uF capacitor to be electrolytic. It's absurd. That kind of information was in any Introduction to Electronics text from the 1940s or 1950s.

          Only high-quality/premium paper capacitors were sealed in metal tubes. These were probably special-ordered by Hammond for high-reliability. Even if they are now leaking DC, you probably won't find them too far from their specified values. This is how paper capacitors were made for the Russian military. So, no, they don't look "normal" because they were specially-constructed premium parts, for their time. The improved encapsulation allowed them to last much longer than their wax-dipped cousins. This was all well-known at the time, but you don't see them that often because they were more expensive. Encapsulation to protect capacitors from environmental contamination from moisture, etc... was one of the big challenges in capacitor construction. We do now have to replace the metal-sealed ones in Hammond preamps, but they served their purpose for decades.

          And, yes, any film or paper capacitor with the appropriate voltage rating will work.
          I'm David. 'Dave' is someone else's name.

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            #6
            Thanks David! All good info to know.
            Hammond L-102 "mobilized", Hammond M-3, Hammond M-101, Hammond T-211, Hohner Cembalet CF, Hohner Cembalet N, Hohner Favor Combo, Hohner Pianet L, Hohner Pianet T, Hohner Symphonic 30N, Leslie "430" (former 130 with horns and light show added), Nord Electro 3, and an entire village of guitars and harmonicas.

            Comment


              #7
              To add more, around 1958, the premium paper capacitors Hammond sourced for their preamps were now sealed in some kind of brown plastic material that seems to have worked even better than the metal jacket system. I have never encountered one of these brown plastic sealed capacitors in a Hammond preamp that has failed. That's not to say that none of them have ever failed, but I haven't seen one, while I have seen failures of the metal jacketed type, which are found in 1940s and 50s Hammond power amps and preamps. Some of these metal jacketed capacitors are still good, but they can't be trusted long-term.
              I'm David. 'Dave' is someone else's name.

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