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Bell Audio 2325 Output Transformer

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  • Bell Audio 2325 Output Transformer

    So I had a couple of Bell Audio units land in my lap and both have bad power transformers. The customer asked me to test the output transformers so he can part them out as the units are not in the best of shape after spending a few decades in an attic. I was getting strange readings with my NE-2 transformer test and decided to download the schematic and saw a setup that was pretty strange to me. Any idea what they are accomplishing tying the cathodes to the OT?
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  • #2
    The cathode windings are just for negative feedback. There was a fad for doing it that way it at the time.
    Experience is something you get, just after you really needed it.


    • #3
      It's a cathode feedback winding used to improve linearity, also employed in the legendary Quad-II hifi amps.

      Such local NFB (another example being screen NFB via UL taps) allows for less global NFB to achieve comparable performance.
      Less global NFB was assumed to cause less stability problems.
      Last edited by Helmholtz; 01-03-2021, 10:17 PM.
      - Own Opinions Only -


      • #4
        Thanks for the replies, I learned something new. I'm going to assume that it wouldn't be easy to substitute this OT in another amp unless it had a similar setup?


        • #5
          WHy? If you don't connect extra windings, they just sit there unused. You don't have to use the feedback windings, you don't have to connect the UL taps.
          Education is what you're left with after you have forgotten what you have learned.


          • #6
            Your right, I see it now.