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KLV 1000 Blows Fuse with Driver Tube installed

Discussion in 'Amplifiers' started by Jason Lawrence, Aug 1, 2018.

  1. Jason Lawrence

    Jason Lawrence New Member

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    Hello all. I have literally inherited a KLV1000 amp. And upon checking it out with a Cobra 29, 2 watt key it blew that 4 amp fuse back by the rectifier circuit. After reading a few post on here about fuse blowing issues, I un- installed all tubes and added them back one by one and re tried each time but didn't see any RF ,but not blowing the fuse either until I got to the last one as the driver. At this point all tubes are back in and it blew upon key. I swapped driver tube out with a final tube and it popped again so I think it is not the tube but the fact it blows with a tube in the socket. When I leave the driver tube out, it doesn't pop but I still do not get any output RF. At one time the relay chattered when I let off the key and the chatter caused the watt meter on the front to jump up to about 800 watts, chattering of course only for a few seconds and it dropped. I don't see anything that looks black or burnt and the tubes all seem to glow. It has the 6KG6A tubes. Any suggestions appreciated, thanks, Jason


     

  2. ExitThirteen

    ExitThirteen Grumpy and Cranky

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    You either have a bad tube in that spot, or there's a short in the tube socket (or by the tube socket), or there's a short between a couple traces on the PCB. Tubes can go short without looking burnt. Swap the tubes around and see if the short follows the tube, or if it's contained to the tube socket or surrounding area. There is an outside possibility that you have a faulty filter capacitor, but usually that will blow the fuse when you power up the amp. Try moving tubes around and see what that does. I think it's a suspect tube. Let us know how you get on.


    ~Cheers~
     
  3. Jason Lawrence

    Jason Lawrence New Member

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    Okay, I will try that. Thanks
     
  4. Shadetree Mechanic

    Shadetree Mechanic 808 On The North Side of Dover

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    Maybe try it with the driver tube in and the others out?
     
  5. Jason Lawrence

    Jason Lawrence New Member

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    Okay, switch the driver with a final tube and the fuse blew. It's like having one in that socket blows it.
     
  6. nomadradio

    nomadradio Analog Retentive

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    This is exactly what we found with the 5-tube version of this amplifier.

    A good tube goes into the driver socket.

    And comes out blown.

    You will need a tube tester to sort out the blown ones from the tubes you can still use.

    There is some sort of critical stability issue with this model's driver-tube circuit.

    Never did find out what.

    The only solution we every found was to modify it to become the four-tube version. Requires some rewiring. Don't have a detailed step-by-step to offer for this. But it's been a while since the last one. I'll have a look for any pics we may still have from back then.

    The four-tube version of the 1000 never does this. Once it's converted from five tubes to four, the problem always went away.

    But sorting out which tubes are still good will be necessary. The flash you see from the driver tube just as the fuse trips usually means permanent damage to the tube that was in the driver socket. You will need four good tubes to run it after the conversion, even if you now have only three that are not damaged.

    73
     
  7. Jason Lawrence

    Jason Lawrence New Member

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    Interesting! Would the end result make it a high drive amp? Only issue with testing the tubes, my B&K Tube Tester is pre70's. There is not a listing for this tube or the substitutes for it. Is there an older tube Novar that I could set it up like just to test? Thanks
     
  8. Tallman

    Tallman W9WDX Amateur Radio Member, KW4YJ EXTRA class

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    Do not key the amp with the covers off, there is a safety interlock that will blow your fuses.
     
  9. Jason Lawrence

    Jason Lawrence New Member

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    Okay thanks
     
  10. Dmans

    Dmans Well-Known Member

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    ExitThirteen,
    I was thinking the same thing but for a different reason. My first thought was that the High Voltage is not high enough to support 5 tubes because of a weak/blown/shorted filter capacitor.

    Nomadradios response sounds like the same possibility??

    Then again, I may be waaaaay off base.

    Good Luck Jason Lawrence

    73's
    David
     
  11. Shadetree Mechanic

    Shadetree Mechanic 808 On The North Side of Dover

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    I was just wondering if this could be made into a straight 5 instead of 1x4? Just letting my mind wander.
     
  12. nomadradio

    nomadradio Analog Retentive

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    Never did try a 'straight 5' solution. Was no reason, since buying more tubes was never on the customer's wish list. Making it work at minimum cost always seemed to be the owner's agenda.

    The base of the EL-509 tube looks like the american 9-pin "novar" all-glass tube base.

    But it's not.

    It's a metric-standard base called "magnoval". The pins are thicker, and that tube will spread out the contacts if you plug it into a normal american-type 9-pin socket. After that, the american-type sweep tubes will be a bit loose in that socket ever after.

    A socket that fits them properly is designed differently.

    An american type number "6KG6" appears to be this same tube. Some testers include that one on the chart, some don't.

    Our Hickok tester has a separate magnoval socket, but most testers won't.

    Best of luck and 73
     
    Dmans and Shadetree Mechanic like this.

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