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Silvertone model 1419 Widow Maker Amp - Installing isolation transformer

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  • Silvertone model 1419 Widow Maker Amp - Installing isolation transformer

    I got this Silvertone 1419 amp that needs a good 1:1 isolation transformer installed. Strange that I have been doing this repair work for a while now and this is just my first time dealing with one of these things. I have sourced a Triad N-68X as a potential candidate to install in this amp. I am pretty sure that this should do the job but is there anything I might be overlooking? After installing the new transformer I realize there is still some changes that will need to be done to the circuit to make it safe. I do not have the 1419 schematic but the 1420 looks to be nearly identical. So first thing to get started on is to get a good transformer.

    Triad-N-68X.pdf
    Silvertone_5XL-14203.pdf
    When the going gets weird... The weird turn pro!

  • #2
    I also have a few small 12v 1A transformers laying around that might prove useful for a heater supply. Would need to regulate it a bit but I think it could work. Might add too much weight but I could completely redesign the amp if I went that route. Could even ditch the rectifier tube and go solid state rectification. Also can I get rid of the other inter-stage transformer if I redesign the amp?
    When the going gets weird... The weird turn pro!

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    • #3
      Originally posted by DrGonz78 View Post
      Also can I get rid of the other inter-stage transformer if I redesign the amp?
      The small second transformer is an isolation transformer that separates the ac line ground from the input audio ground. So in theory the input ground is already ac isolated.

      In normal widow-makers, the 12 volt filament is also in series with the rectifier and the output tube filaments.

      Comment


      • #4
        So now back to this thing that has been sitting waiting for me to get around to it. I have the Triad N-68X isolation transformer and I want to ditch the T2 transformer to gain ample enough room to mount the isolation transformer. I have read around for a bit on this and gathered two proposed ways of wiring in the isolation transformer. I intend to involve a full bridge rectifier as I read that it helps keep the Triad N-68X from running hot. I am posting two different ways that the heater filaments could be wired up after this conversion and just looking for some advice on this matter. Also, please note that the tube rectifier (half-wave) will still be installed and I have left it off of this drawing at this time.
        Click image for larger version

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        With the half-wave bridge installed it will resemble this power supply in this schematic for the Pepco amp. This wiring shows
        https://music-electronics-forum.com/...3&d=1374983142
        When the going gets weird... The weird turn pro!

        Comment


        • #5
          I am curious how others members of MEF have approached the heater filament wiring on these amps. Do I leave the T2 transformer in place? Or if I remove it what is the best wiring method for the filaments?
          When the going gets weird... The weird turn pro!

          Comment


          • #6
            What an odd design. Honestly I would just use an isolation transformer and be done with it. Btw.. is this amp yours or a customers? There is nothing magical about these amps imho. If it’s your own and you are changing transformer, rectifiers, etc.. you could just rebuild it into something else you might like better... like a Champ.

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            • #7
              This is an amp I have from my uncle to fix up and then we will sell it. He is very patient about some of these amps and allows me to take my time. In fact this amp represents more a learning lesson for modifying a hot chassis designed amp. The chassis is not the most heavy duty and the cab is pretty much crap too. So mounting the isolation PT in the cab doesn't seem like a good idea. I could keep T2 transformer on the amp and mount the isolation tranny inside the chassis, but then I would think it would not get good air circulation.
              When the going gets weird... The weird turn pro!

              Comment


              • #8
                Funny enough, I'm doing the similar gag here. a 1420 with a similar schematic. What did you end up doing? I was gonna do what OldDawg suggested.

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                • #9
                  I installed a 1:1 transformer. Note that some 1:1 transformers put out a higher secondary than 120v mains. So I reversed the transformer so it would not step up my B+ voltage. I installed a full bridge rectifier and that went into the half wave rectifier. The voltages were fine and it passes signal but the amp is way noisy. I put it on the back burner for while.

                  I decided that I am going to install a 6v filament transformer. For the power tube I will install a 6CU5 and keep the 12au6 in the preamp. So basically it becomes a normal tube amp. Then I am gifting the amp to my cousin for his first tube amp.
                  Last edited by DrGonz78; 01-16-2021, 06:58 PM. Reason: wrote 6au6 but meant 12au6
                  When the going gets weird... The weird turn pro!

                  Comment


                  • #10
                    I have a 'No Name' amp on the bench at the moment. (similar to a Wards Airline GDR-8611A)
                    Installed a N68X.
                    The 12AU6 is really amplifying the 60 Hz ripple. (as it did before the 1:1 was installed.)
                    Filter capacitors are new.
                    Very annoying to say the least.
                    Applying a signal directly in to the output tube results in zero hum.
                    Not too sure if a bridge rectifier would help or not (supposedly it helps the 1:1 transformer).
                    Attached Files

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                    • #11
                      I don't like working on these series filament pieces of crap amps. So isolate the preamp tube on a "real" amp, simply pull the tube from the socket. Viola!! If I ever do anything to a widow maker type amp again it will be to make it un-widow made.
                      When the going gets weird... The weird turn pro!

                      Comment

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