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Sourcing am unkown transformer with goofy taps

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  • Sourcing am unkown transformer with goofy taps

    Hey Y'all,

    I'm trying to find a replacement transformer for a PILOTONE AA-902A, a very cool monoblock amp from the 50's. I have the schematic and another working AA-902A, so usually I would start by measuring voltages, but it has something I've never seen before- the HV secondary connects into another secondary after the DC voltage leaves the rectifier; Click image for larger version

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    I have another working monoblock of the pair, I could measure AC off of the Yel-Red to get what I need, but how would I go about figuring out what the Yel secondaries should be rated at, What is their purpose? Am I approaching it the wrong way, is it much simpler than I'm trying to make it? And finally, is there a modern replacement out there anyone could suggest?


    Thanks!



  • #2
    The Yel-Yel wires are the 5V heater supply for the 5Y3. Nothing uncommon here. The heaters of directly heated tube rectifier are always floating on B+, as the heater is the cathode.
    - Own Opinions Only -

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    • #3
      Originally posted by Helmholtz View Post
      The Yel-Yel wires are the 5V heater supply for the 5Y3. Nothing uncommon here. The heaters of directly heated tube rectifier are always floating on B+, as the heater is the cathode.

      Wow can't believe I missed that one. Thanks Heimholtz!

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      • #4
        So I'm realizing now I've never sourced a transformer by voltages alone would just need to find something like:

        120 VAC primaries,
        HV secondaries ??? 350-0-350?
        5VAC Rectifier Filiment
        6.3VAC Filiment

        If my rectified goal is 365V (Or a little more for 6L6's... I'm going off an attached schematic for the 6v6 version)...

        Here's a classictone HiFi transformer; it says 342VDC B+ with a 5y3, could I use that with a gz34 to bump it up to 6L6 voltages? Is that even necessary?
        http://www.classictone.net/40-18086.pdf

        Or perhaps this hammond would be better?
        https://www.hammfg.com/files/parts/pdf/278CX.pdf
        Attached Files
        Last edited by Mr_bibbles; 02-18-2021, 05:24 PM.

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        • #5
          The Classic Tone should get the job done. The Hammond is WAY WAY WAY too big in every way. Check the dimensions.

          The Pilot amp uses an old version of the 6L6, the 6L6GB. That version of the tube was only rated at 360V IIRC. So don't expect to get 50W from a pair. You are more likely to get 25-30W. The transformers and the whole design of the Pilot amp are focused around that. You can't make simple changes to get to 50W without rebuilding the whole thing, and you'll need a new set of transformers.

          WARNING! Musical Instrument amplifiers contain lethal voltages and can retain them even when unplugged. Refer service to qualified personnel.
          REMEMBER: Everybody knows that smokin' ain't allowed in school !

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          • #6
            Only one problem with Classictone

            Just received this in an email. Sad as they made some quality iron in my opinion.

            “After 10 years of producing ClassicTone transformers and 78 years of manufacturing, Magnetic Components is announcing the permanent closure of our factory in early November.

            This notice is much shorter than we had anticipated. This is a result of COVID and a recent and serious supply chain issue that has developed. Overall, in the last 4 years we have seen a large decline in the tube amp transformer market. At the same time, we experienced unprecedented increases in all costs necessitating us to make this tough, final decision to close.

            We have decided to shut down voluntarily and before the business situation potentially gets worse. We want to close our third-generation USA-based company with dignity and honor.

            We are no longer accepting new orders directly. ClassicTone tranformers are available now only from our resellers while supplies last.

            We appreciate all of your support throughout the years and wish you the best of luck.

            Thank you so much!

            Magnetic Components, Inc.
            (ClassicTone line of Vintage Constructed Amp Transformers) “
            Binkie McFartnuggets‏:If we really wanted to know the meaning of life we would have fed Stephen Hawking shrooms a long time ago.

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