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Blown Transformer on 2006 Carvin V3

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  • Blown Transformer on 2006 Carvin V3

    I have the original version of the Carvin V3 Head. I believe it's power transformer went out because I measure 5 ohms between hot and return of the IEC when I flip the mains "on" while unplugged. 6A circuit breaker inline tells me I know the transformer should be at a minimum 20 ohms (the circuit breaker flips off within 1 second of turning the amp on). I looked up the V3 schematic and found the transformer to be 15-10714. That's all the information I can find on it. Does anybody know this transformer by another name, who makes it, how to get a replacement, was it proprietary to carvin, any information about it? Thanks.

  • #2
    I believe it's power transformer went out because I measure 5 ohms between hot and return of the IEC when I flip the mains "on" while unplugged. 6A circuit breaker inline tells me I know the transformer should be at a minimum 20 ohms
    I think you are mixing up DCR and primary impedance. Such low primary DCR values are not uncommon with PTs.

    Does the circuit breaker trip with all secondary wires disconnected?
    Last edited by Helmholtz; 01-20-2020, 10:20 PM.
    - Own Opinions Only -

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    • #3
      Originally posted by Helmholtz View Post
      Does the circuit breaker trip with all secondary wires disconnected?
      Yeah it still trips even with the secondary wires' connector unplugged from the PCB, so that leaves me to the IEC, power transformer, or circuit breaker. I guess you have a good point that I shouldn't have jumped to the power transformer from the low DCR since this is AC current which will have more resistance from the 'inductor'. Any other troubleshooting tips? Thanks!

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      • #4
        You can test transformers using the neon bulb trick:

        https://www.premierguitar.com/articl...ormer-tester-1
        --
        I build and repair guitar amps
        http://amps.monkeymatic.com

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        • #5
          This appears to be a pretty simple tube PT, no low voltage windings for op amps or anything, no tube rectifier heaters either.

          Click image for larger version

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          Maybe something like the Edcore XPWR002? https://www.edcorusa.com/xpwr002

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          • #6
            Originally posted by xtian View Post
            You can test transformers using the neon bulb trick:

            https://www.premierguitar.com/articl...ormer-tester-1
            So I don't have a neon bulb; however, I do have a multimeter. Using a 9V battery in the same manner he used the 6V battery, the secondary coil (700V to 120V input) only jumped to 1V each time. The highest I could get it to jump was to 4V. I would expect somewhere in the 60V range for a 7:1 turn transformer using this trick. Thanks for the idea, but I'm still left thinking the transformer is toast. Here are some pictures. Looks a little....liquidy... on the top there.

            https://i.imgur.com/2q0eAD5.jpg
            https://i.imgur.com/PoM6pCB.jpg

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            • #7
              Thanks for the tip about edcore. I found this one https://www.tubeampdoctor.com/en/mai...nmQaCyv0E2Pek0 which shows 400mA at 345V and 7.5A at 6.3V. Assuming that website is correct, it looks like edcore does have an option to meet that: https://www.edcorusa.com/xpwr127?fbc...th-iu8XDuPIjcc Not sure how I feel about the 8 week lead time though.

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              • #8
                So I don't have a neon bulb; however, I do have a multimeter. Using a 9V battery in the same manner he used the 6V battery, the secondary coil (700V to 120V input) only jumped to 1V each time. The highest I could get it to jump was to 4V. I would expect somewhere in the 60V range for a 7:1 turn transformer using this trick.
                You can't replace the neon with a multimeter. The principle is magnetic (self) induction and works similar to a spark coil. Disconnecting the battery interrupts the current and produces a large but short flyback voltage spike that overcomes the ignition voltage of the neon lamp. Other than a neon discharge lamp a meter conducts all the time and thus prevents a large voltage spike. Also meters are much too slow. The neon lamp doesn't conduct below its ignition voltage of 60V to 80V and reacts very fast.

                But I agree your PT looks toasted.

                There are other methods to test a transformer. Do you have a bulb limiter? Or some other PT that delivers heater voltage?
                Last edited by Helmholtz; 01-21-2020, 07:26 PM.
                - Own Opinions Only -

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                • #9
                  Originally posted by Helmholtz View Post
                  You can't replace the neon with a multimeter. The principle of the test is based on (self) induction. Disconnecting the battery interrupts the current and produces a large but short flyback voltage spike that overcomes the ignition voltage of the neon lamp. Other than a neon discharge lamp a meter conducts all the time and thus prevents a large voltage spike. Also it's too slow. The neon lamp doesn't conduct below its ignition voltage of 60V to 80V and reacts very fast.

                  But I agree your PT looks toasted.

                  There are other methods to test a transformer. Do you have a bulb limiter? Or some other PT that delivers heater voltage?

                  I see your points on a multimeter vs the bulb. I don't have a bulb limiter either, nor other PT unless I pull one out of my Dr Z. I put this PT back in the carvin and turned it on again, just to make sure the problem continued to be repeatable and of course it was. This time I paid attention to the LEDs which always flash on immediately with power. The breaker popper after about 1 second, but during that 1 second, no LEDs turn on, the lamp bulb doesn't turn on, nothing even flickers. I'm fairly confident the PT isn't working at all.

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