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  • "multisection" capacitors help

    OK. I'm kind of "visual" guy... sorry for the basic question - I came across multisection cap in an Ampeg B15N that I'm restoring right now. I have already changed bias cap, and one of the 30uf 600v filter caps. The one that is odd is a 3-section capacitor. It's a 40/40/40-500V. I see that each section has its own symbol like triangle, square, etc. They look like they're having common ground (black)?

    I need to replace it by three regular caps, as the multisection cans are super expensive.
    So, am I thinking right:

    #1 40uf /500V (+) goes to yellow and (-) goes to common black ground
    #2 40uf /500V (+) goes to red and (-) goes to common black ground
    #3 40uf /500V (+) goes to orange and (-) goes to common black ground

    Like the image below:
    Click image for larger version

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  • #2
    Originally posted by boroman View Post
    OK. I'm kind of "visual" guy... sorry for the basic question - I came across multisection cap in an Ampeg B15N that I'm restoring right now. I have already changed bias cap, and one of the 30uf 600v filter caps. The one that is odd is a 3-section capacitor. It's a 40/40/40-500V. I see that each section has its own symbol like triangle, square, etc. They look like they're having common ground (black)?

    I need to replace it by three regular caps, as the multisection cans are super expensive.
    So, am I thinking right:

    #1 40uf /500V (+) goes to yellow and (-) goes to common black ground
    #2 40uf /500V (+) goes to red and (-) goes to common black ground
    #3 40uf /500V (+) goes to orange and (-) goes to common black ground
    Your assumption is correct, and your solution looks good. I expect your B15's power supply will be happy with that.

    Those Tube Amp Doctor filter caps look very small - but if they work, that's what counts.
    This isn't the future I signed up for.

    Comment


    • #3
      Originally posted by Leo_Gnardo View Post
      Your assumption is correct, and your solution looks good. I expect your B15's power supply will be happy with that.

      Those Tube Amp Doctor filter caps look very small - but if they work, that's what counts.
      Ha! Those are my weak Photoshop skills. In fact, they're larger!

      Comment


      • #4
        Just curious - can I use 47uF in that section (instead of 40uF)?

        Comment


        • #5
          Originally posted by boroman View Post
          Just curious - can I use 47uF in that section (instead of 40uF)?
          Yes.

          What I often do with B15's is remove the "twistlok" multisection cap, replace it with a 50+50 uF 500V dual cap - lately F&T brand - but I have to install a bracket to hold the 50+50. Then only one cap section needs to be an individual.
          This isn't the future I signed up for.

          Comment


          • #6
            Originally posted by boroman View Post
            Just curious - can I use 47uF in that section (instead of 40uF)?
            Sure!
            - Own Opinions Only -

            Comment


            • #7
              Maximum filter for a GZ34/5AR5 is 60uF, and 47uF is less than 20% over 40uF, so that should be fine.
              It's weird, because it WAS working fine.....

              Comment


              • #8
                I've done this in the past by using an inexpensive dual 50uf + 50uf 500V radial can cap plus a single axial 47uF 500V.
                Experience is something you get, just after you really needed it.

                Comment


                • #9
                  What a news! thanks @Randall

                  Originally posted by Leo_Gnardo View Post
                  What I often do with B15's is remove the "twistlok" multisection cap, replace it with a 50+50 uF 500V dual cap - lately F&T brand - but I have to install a bracket to hold the 50+50. Then only one cap section needs to be an individual.
                  Whoah.. too much mathematics for me prbably. How you'd replace 30uf and 40/40/40 with 50/50?

                  Comment


                  • #10
                    50/50 replaces two sections of the 40/40/40, and then an additional capacitor for the other 40. The 30 uF would be another cap.
                    Last edited by Bloomfield; 09-03-2019, 08:50 PM. Reason: missed 30uF

                    Comment


                    • #11
                      OK. Now the hard part... Need some help as my head will explode :/ My friend brought to me an Ampeg VT40 (which is a combo version of a V2 head), that he took out of the car and during rain transported to the club and (silly) connected to the main power. He saw tube crackling so immidiately turned it off. I have replaced some of burned resistors and little caps (along with the 20+20 cap that had leak).

                      Now, I have turned it on (without power tubes) and saw sparks show around the C20 70/40/40 cap and leg of 100k resistor. You can see on the picture it's burned to black, one leg. It has burned now. I unsoldered the resistor and it measures fine. I want to replace that cap but I don't see 70/40/40 in Europe. But seeing schematic it uses only 70 and one 40 section, right? (the third, 40uf section isn't used? But ground of the thrid section is....). How to do it right? I know the best way would be getting 70/40/40 and solder it like it was before, but maybe is there any simpler solution?

                      Click image for larger version

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                      EDIT: both big caps 70/40/40 and 40/20/20 are bad and leaked... So, is there any way I could replace those with single ones available? And how do I connect that mess?

                      Click image for larger version

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                      Click image for larger version

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                      Last edited by boroman; 09-14-2019, 11:02 AM.

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                      • #12
                        Originally posted by boroman View Post
                        EDIT: both big caps 70/40/40 and 40/20/20 are bad and leaked... So, is there any way I could replace those with single ones available? And how do I connect that mess?
                        Yes, good choice to replace both multisections. What I do in cases like these, get dual can caps with "close enough" values. The capacitance does not have to be exact, keep that in mind. Lately I've been using F&T 50+50 / 500. F&T are German made, Antique/tubesandmore.com carry them in the US. Hope you can find some in Canada.

                        After having a look at the schematic to refresh my memory, things are a little more complicated than simply swapping in fresh can caps. Ampeg uses a series connection to enable higher B+ voltage. Fortunately the negative pole on the F&T & similar caps is brought out on a connecting pin. To simulate Ampeg's main B+ filter use two 50+50 caps in series. Jumper the + terminals on each cap, now you have 100 uF caps. DO wrap the 50+50 cap cans with an extra layer of quality electrical tape where they are held by the bracket. The outer can may be connected to the - terminal, and in Ampeg's design, neither of the - terminals are to be connected to ground so a little extra insulation is all to the better.

                        Use a pair of individual 47 uF 500V caps to replace the series cap filter Ampeg uses for the second hi voltage filter. It would be a good idea to parallel each cap with a resistor, 2 watt 100K to 330K to balance their DC potentials. You may want to use tie strips to mount these individual R's & C's.

                        A pair of balancing resistors across the first stage filter caps would also be a good idea.

                        Let's hope that's all that's needed... well not exactly. DO replace your bias filter cap while you're at it. Even if it's not bad - yet - swapping in a fresh one is "cheap insurance".

                        Hope you can revive that VT40 - they're terrific sounding amps. I fixed one up & had it sitting around here for a decade before someone bought it - then he sold it to Earl Slick. Earl called up & we had a chinwag about it - he agreed with my opinion "it's the sound of the Stones in the 70's" - classic! - everything from Exile to Some Girls.

                        NOTE: To try & prevent the "exploding head" feeling, let's have a look at how Ampeg deploys their filter caps. First, one is a 40 + 20 + 20 uF with all 3 sections paralleled so effectively it's 80 uF. That cap is connected in series with the 70 uF section of another can cap. Theoretically they should be the same, but here's Ampeg to prove once again "close enough for rock n' roll" is plenty adequate. We can apply fancy formulas, and what we'll find is the effective capacitance is somewhere around 37 uF. When the can caps are replaced with dual 50's, each parallel wired, the result is 50 uF. A little more filter, less hum from the B+ supply, no harm done, in fact a little better than straight from the factory.

                        FWIW you'll have the devil of a time finding 70 uF in can caps anyway. So avail yourself of what can be found these days & don't worry.
                        Last edited by Leo_Gnardo; 09-14-2019, 02:19 PM.
                        This isn't the future I signed up for.

                        Comment


                        • #13
                          When recapping oldtimers (vintage) amplifiers, original capacitors of appropriate values cannot always be found. It is therefore necessary to adopt the first approximate value that is produced.
                          The installation of "fresh" capacitors of approximate values, does not damage the amplifier and is much better than the search for "vintage" parts, because the time done its thing (insulation resistance, leakage current, loss factor, etc.)
                          Formatting old capacitors in order to keep the amplifier in its original state is only a temporary measure with an uncertain result.
                          The connection of "fresh" capacitors in parallel with the old capacitors is not recommended because the loss factor (tgδ) of the old capacitor is still present.

                          Click image for larger version

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                          Recapping Ampeg V2

                          C19 (40 + 20 + 20 = 80uF) replaced with 100uF
                          C20 (part 70 = 70uF) replaced with 100uF
                          Original C19 (80uF) in serias with C70 (70uF) = 37.33uF
                          Replacing C19 (100uF) in serias with C70 (100uF) = 50uF
                          Replacement is OK

                          C18 (40uF) replaced by 47uF
                          C20 (part 40 = 40uF) replaced with 47uF
                          Replacement is OK
                          It's All Over Now

                          Comment


                          • #14
                            It's also useful to remember that old caps had a very wide tolerance. -20%/+80% were common. I see a lot of old caps that read high compared to their nominal value.

                            Comment


                            • #15
                              Originally posted by Mick Bailey View Post
                              It's also useful to remember that old caps had a very wide tolerance. -20%/+80% were common. I see a lot of old caps that read high compared to their nominal value.
                              My cap meter reads leaky caps as if they have higher than expected values, say 40 to 200% over. If I'm reading an old cap say 40+ y/o I interpret "bonus" capacitance as leakage, not a magic advantage by far. And those caps are destined for replacement anyway, so if I read their value, it's mostly for amusement. Occasionally I find one that reads a small fraction of its rated value, of course that means it's headed for the rubbish bin, for sure!
                              This isn't the future I signed up for.

                              Comment

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