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5e3 power transformer?

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  • 5e3 power transformer?

    hey guys, i have a 5e3 amp here on the bench and the guy that owns it says in just stopped working after a gig.
    He thinks it may be the power transformer. i opened up the amp and there are no visible signs of any bad,burnt,blown components. the amp keeps blowing fuses when turned on. i have the power tranny taken out of the amp and it's a weber wo25130 power tranny. i did a ohm check on the following leads and here's what i got.

    Primary- 3.4 ohms
    secondary- two red ht together=16.7ohms, one red with ct =33.4ohms, other red with ct =48.7ohms.
    - two 6.3 heater windings together =.4 ohms. with ct .4ohms each.
    - two yellow =.5 ohms.

    the tranny has two red ht @680v/150ma and two whit/red ht @540v. If it is the the 680v ht that is the problem, can i use the 540v winding instead?

  • #2
    Transformers are usually the last thing I suspect. They rarely fail. Since you already have it out of the amp, I would apply power to the primary via a light bulb limiter or current limiter, if you have one, and measure the secondary to see exactly what it's doing. You could also bring it up slowly on a variac while monitoring current. If it still draws massive current with no load, then it's bad.
    Last edited by The Dude; 05-04-2018, 10:14 PM.
    "Yeah, well, you know, that's just, like, your opinion, man."


    • #3
      ^^^ The Dude is right!

      It looks to me from the readings you posted the PT is fine, put it back and pull rectifier tube and output tubes, still blowing fuses?


      • #4

        give it a try.


        • #5
          As to your second question, if the 680V winding is shorted, you won't be able to use the 540V tap either.
          "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


          • #6
            hey guys, thanks for all the replies. I hooked it up to my current limiter like dude suggested and the bulb lit up like a christmas tree. I guess that says everything, internal short.


            • #7
              Well, that's a bummer. It should draw almost no current unloaded.
              "Yeah, well, you know, that's just, like, your opinion, man."


              • #8
                ya, it's a bummer for sure. Thanks again for all your help.