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Vox ac15tb > ok with a 16ohm spkr?

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  • Vox ac15tb > ok with a 16ohm spkr?

    Hi chaps- as title really, I have a vintage celestion greenback 12" that is unfortunately 16ohms.. which I'm itching to try.

    The vox ac15tb (uk made, marshall factory late 90's?) has only one output for its 8ohm spkr.

    Is it ok to give it a try? I will only have vol on say 2 max.. nothing hammer & tongs.

    thanks SC

  • #2
    If there is no 16 Ohm tap, keep the levels down a bit and all will be fine.
    Support for Fender, Marshall, Mesa, VOX and many more. https://jonsnell.co.uk

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    • #3
      Originally posted by Jon Snell View Post
      If there is no 16 Ohm tap, keep the levels down a bit and all will be fine.
      Ok thanks- just tried it & seemed happy at low vols. Is there no way I could just use this speaker instead of the vox blue 8ohm?

      thanks SC

      Comment


      • #4
        The schematic shows 2 outputs on the OT https://el34world.com/charts/Schemat...x_ac1596pa.pdf
        That seems worth investigating.
        My band:- http://www.youtube.com/user/RedwingBand

        Comment


        • #5
          Originally posted by pdf64 View Post
          The schematic shows 2 outputs on the OT https://el34world.com/charts/Schemat...x_ac1596pa.pdf
          That seems worth investigating.
          Hi there pdf. Thanks for looking at my schematic.. as i have the back off i can see the black and green wires going to the 8 ohm jack, but no sign of any other wires, let alone any going to a nice 16 ohm jack. Ot on other side so will remove amp tmrw to see what secondary wires. Interesting tho.

          If it was possible, if i did find a redundant pair of 16 ohm wires.. what would be the inherrant difference from the two spkrs? Half in volume from the 16 ohm?

          Comment


          • #6
            pdf64 hi, I'm trying to figure out how you could establish this 16ohm tap exists, from looking the schematic.

            Ok I see an xfmr lower rhs on the schematic, & looking physically inside my amp, I see two wires coming from each el84 tubes, going behind to the OT. These seem to match the schematic. So I must assume this lower rhs xfmr is the OT.

            But there's nothing designating 4,8,16 on the schematic.. no information at all in fact not even the one I know exists/ used @ 8ohms.

            Is there another page you viewed, or know the "294-310" coded OT maybe to determine this 16ohm tap exists?

            thx SC

            Comment


            • #7
              The circuit supplied is from 1996 so we presume it is correct.
              The original VOX AC15/30 had a terminal strip for the speaker output with 7.5 or 15 Ohm tappings, (now known as 8 or 16 Ohm).
              The transformer shown looks like it has a split tapping for 8 or 16 Ohm, if the part is the same it will need a bit of knowledge to work out what is what but no harm will come to the amplifier on a 16 Ohm load.
              Click image for larger version

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              Support for Fender, Marshall, Mesa, VOX and many more. https://jonsnell.co.uk

              Comment


              • #8
                It's started ...
                Welcome to the Machine.


                Who does not know and knows that he does not know - teach him Confucius)
                Who knows and does not know that he knows - wake him Confucius)

                Comment


                • #9
                  Originally posted by Jon Snell View Post
                  The circuit supplied is from 1996 so we presume it is correct.
                  The original VOX AC15/30 had a terminal strip for the speaker output with 7.5 or 15 Ohm tappings, (now known as 8 or 16 Ohm).
                  The transformer shown looks like it has a split tapping for 8 or 16 Ohm, if the part is the same it will need a bit of knowledge to work out what is what but no harm will come to the amplifier on a 16 Ohm load.
                  Click image for larger version

Name:	Screenshot 2021-03-28 at 09.14.13.png
Views:	139
Size:	364.6 KB
ID:	927699
                  Hi Jon. Ok I can see you've kindly added/ overlaid (or someone has) "output transformer, com/ 8/ 16". Is this addition based on: your knowledge of this OT? or some online info? or.. is it that the schematic layout just indicates to you knowing how these things work, that this extra 16ohm tap exists maybe because it's -above- the 8ohm one (& so you might just know that a 'central' one is always 8 ohm-??) I'm thoughrally confused by how you can determine the existance of this 16ohm tap, likewise pdf64, if that is.. as i asuume.. you might have overlaid/ added the info in bold here to my schematic info.

                  Or can you maybe say where this diagram has been obtained from if it wasn't you whose added the bold info? thx SC

                  Comment


                  • #10
                    Is there another page you viewed, or know the "294-310" coded OT maybe to determine this 16ohm tap exists?
                    output transformer for the VOX AC15 REISSUE Replaces TXOP00008. (294-310)
                    https://www.tubeampdoctor.com/en/output-transformer-for-vox-ac-15-reissue-upgrade
                    Attached Files
                    Who does not know and knows that he does not know - teach him Confucius)
                    Who knows and does not know that he knows - wake him Confucius)

                    Comment


                    • #11
                      The original design, I am led to believe is this one; Click image for larger version

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Views:	129
Size:	716.6 KB
ID:	927708
                      https://trans-amp.co.uk/productinfor...ml?item=TT3123
                      Support for Fender, Marshall, Mesa, VOX and many more. https://jonsnell.co.uk

                      Comment


                      • #12
                        Originally posted by Jon Snell View Post
                        The original design, I am led to believe is this one; Click image for larger version

Name:	Screenshot 2021-03-28 at 11.15.23.png
Views:	129
Size:	716.6 KB
ID:	927708
                        https://trans-amp.co.uk/productinfor...ml?item=TT3123
                        Hi Jon. Ok but I can't understand how this relates to my OT, if I was trying to determine something absolutely specific about it, & this info is of an entirely different one. I am as usual with amp xyz utterly lost sorry.

                        I think you might be implying that the designers of mine, if it a true reissue down to the nth degree (I have no way of ascertaining if this is modern design principles at all).. will have therefore chosen an exact-wiring-replica of the original.. therefore as it used to have both an 8 ohm & 16ohm tap.. therefore mine will have too.. therefore the extra tap (if that's what it has) MUST be a 16ohm, concluded by logic.

                        But I have no idea.

                        Comment


                        • #13
                          I see what you mean.
                          Without a photo I have only the words of this thread to go by.
                          Can you post a photo or look at the three wires that go to the EL84s as the other two or hopefully three wires will tell us what is what.
                          If there are three wires, it has a 16 Ohm tapping.
                          Support for Fender, Marshall, Mesa, VOX and many more. https://jonsnell.co.uk

                          Comment


                          • #14
                            Originally posted by Sea Chief View Post

                            Hi Jon. Ok I can see you've kindly added/ overlaid (or someone has) "output transformer, com/ 8/ 16". Is this addition based on: your knowledge of this OT? or some online info? or.. is it that the schematic layout just indicates to you knowing how these things work, that this extra 16ohm tap exists maybe because it's -above- the 8ohm one (& so you might just know that a 'central' one is always 8 ohm-??) I'm thoughrally confused by how you can determine the existance of this 16ohm tap, likewise pdf64, if that is.. as i asuume.. you might have overlaid/ added the info in bold here to my schematic info.

                            Or can you maybe say where this diagram has been obtained from if it wasn't you whose added the bold info? thx SC
                            The inlay was to demonstrate what you are looking for.
                            Support for Fender, Marshall, Mesa, VOX and many more. https://jonsnell.co.uk

                            Comment


                            • #15
                              Originally posted by Sea Chief View Post

                              Hi there pdf. Thanks for looking at my schematic.. as i have the back off i can see the black and green wires going to the 8 ohm jack, but no sign of any other wires, let alone any going to a nice 16 ohm jack. Ot on other side so will remove amp tmrw to see what secondary wires. Interesting tho.

                              If it was possible, if i did find a redundant pair of 16 ohm wires.. what would be the inherrant difference from the two spkrs? Half in volume from the 16 ohm?
                              The schematic shows 3 terminals on the OT secondary; starting from the bottom, they will typically be common, 8ohms and 16ohms. The 8ohm output will be taken from the common and 8ohm terminals. A 16ohm output would be taken from the common and 16ohm terminals.
                              There is the possibility that the 3 terminals are common, 4ohms and 8ohms.
                              If you can identify the 3rd terminal then it will be possible to work out whether it is intended to be 16 or 4ohms.
                              The terminals may be in the form of wires (colour coded) emerging from the OT, or as solder terminals (also referred to as 'lugs') mounted on the OT. Wire colour codes are typically specific to a manufacturer, they are not generic.
                              I hope that made sense?
                              My band:- http://www.youtube.com/user/RedwingBand

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