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  • Single Ended Stereo Amp

    Hello,

    I want to build and HIFI tube amp for my home. One of the main objectives would be reuse all the components that I can.

    I've recover one UPS transformer.

    - 8V-0-8V secondary that can handle 2,7A more or less.
    - 16V-0-16V with 1A more or less
    - 0-252V without CT

    This transformer can handle two 6L6GC and two 12AX7 without any problem ( I think ).

    I've a bunch of 6L6GC and 12AX7 tubes

    I've a 10H 150mA choke.

    But the schematic that I have uses two 6SN7GT tubes and a pair of 6V6GT output tubes in a single ended configuration.

    My question is:

    I can swap the 6V6GT with the 6L6GC output tubes?

    In single ended config, with 6L6GC I win 2 watts per channel.

    I can swap the preamp tubes with a 12AX7?

    What changes I will need to make?

    Thanks.

    https://ibb.co/4ZZcdG1

    https://ibb.co/pJScLTw

    https://ibb.co/n1srC0s

    https://ibb.co/PDLNCF2

  • #2
    Hi

    This transformer can handle two 6L6GC and two 12AX7 without any problem ( I think ).
    Not sure how you determined that. The 0-252 wires are your mains - the power from the wall outlet. Depending on where you are you use the 0 and the 120 or the 220 or the 240v to wire to the mains. That leaves you with the 16-0-16, which makes about 20vDC. And the 8-0-8 which makes about 11vDC.

    Your tubes all require 6.3vAC for the heaters. You could use DC for that, but The voltages are wrong as they come out. You'd need to use some resistors or something to drop that 8v down a couple. And then there is the thorny problem of no high voltage for the tubes. If your 252 had been a secondary we could have used it, but it is not. You have no high voltage winding.
    Education is what you're left with after you have forgotten what you have learned.

    Comment


    • #3
      My mains are 0-225. And the 0-252 are a secondary, I'm sure about that.

      I determined the amps, simply connecting three 6L6GC into the 0-8v widding, multimeter in series and draws a total of 2,7A AC and only 1v drop.

      Comment


      • #4
        OK, please look again. If 0-252 is a secondary, then where is your mains winding? I only see 16v, 8v, and 252v windings.

        So you had the tubes running on 7v?
        Education is what you're left with after you have forgotten what you have learned.

        Comment


        • #5
          The mains are 0-225V. I check with a serial lamp, all the winding's light the bulb. The only pair of winding's that don't light are 0-225V. Remember that is a UPS transformer.

          Comment


          • #6
            I get a warning saying the links are a security risk and Firefox cannot connect.

            You can build a hifi amp with what you have. The HT will be on the low side but I have an amp running 2x6L6 off a 240v secondary (a 1:1 isolation transformer) that has ample headroom and volume for home listening I would parallel the 8v windings and use a dropper resistor to get the loaded voltage to 6.3v

            Comment


            • #7
              I would parallel the 8v windings
              Paralleling would only be possible with 2 separate 8V windings, but it looks like a single 16V winding with CT.
              - Own Opinions Only -

              Comment


              • #8
                Ah, yes. I overlooked that.

                Comment


                • #9
                  Okey...

                  I'm a newbie, a big newbie. This transformer hasn't mains windings... what a mistake.

                  But if I use the low side for the HT there is no danger of shock or someting like that? this winding are not isolate...

                  sorry about that...

                  Comment


                  • #10
                    Actually the mains is what it does have. It is the high voltage winding it lacks. The 120/220/250 or whatever they were is your multitap mains winding. You use the zero wire with whichever one of those is closest to your mains.
                    Education is what you're left with after you have forgotten what you have learned.

                    Comment


                    • #11
                      There are 2 white wires there that I don't see any labelling for (on the 8-0-8V side). I had thought maybe they were the mains.

                      "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

                      Comment


                      • #12
                        This two white wires are a thermistor.

                        Comment


                        • #13
                          Ok then. It is strictly as descibed by Enzo. Multi-tap primary (choice of 196,225, or 252V).
                          8-0-8V and 16-0-16V secondaries.
                          "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

                          Comment


                          • #14
                            I had a rackmount UPS module recently for evaluation and that had a large toroidal mains transformer with 230v primary and secondary, so a UPS of the correct type is capable of furnishing a transformer that could provide a HT supply. It was the line-interactive section - there was no battery or inverter unit (optional extra). On its own it could be used as a power conditioner. The main issue with this particular one was the size and weight of the transformer due to being rated at 16A@230v.

                            Comment

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