Fuse keeps blowing.

Discussion in 'General Technical Questions and Answers' started by W1RLP, Feb 6, 2020.

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  1. W1RLP

    W1RLP Ham Member QRZ Page

    My Kenwood ts820 I switch on the power and everything remains ok and when I switch on the heater and in less than a minute the fuse blows and I just replaced the finals???
     
  2. K7TRF

    K7TRF Premium Subscriber QRZ Page

    What do you see for plate current between the time you flip the heater switch and the fuse blows? Does this happen with the rig set to Tune mode (while receiving or transmitting)

    A few possibilities come to mind:
    - Bias problems that allow the tubes to go into full conduction even in RX mode once the filaments heat up.

    - One of the new tubes has a short.

    - HV filter cap problems though the heater switch relationship is strange.
     
  3. W1RLP

    W1RLP Ham Member QRZ Page

    Is it possible to install the tubes wrong
     
  4. W1RLP

    W1RLP Ham Member QRZ Page

    If a tube has a short is there a way to tell
     
  5. K7TRF

    K7TRF Premium Subscriber QRZ Page

    Unless you’ve accidentally broken off the base center key you really can’t install a 6146 wrong.

    Without a tube tester it’s hard to test for tube shorts ( you could try an ohm meter from grid pin to anode or filament pins but a lot of tube shorts don’t present as direct DC shorts). I’d probably pull the tubes to see if the fuse problem stops but I’d also check the negative bias supply and If you still have original HV, screen and rectifier caps I’d think about replacement.
     
  6. W1RLP

    W1RLP Ham Member QRZ Page

    K7TRF THANK YOU and since it started when I replaced the finals I will have the tubes tested.
     
  7. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Remember, there's no such thing as a "new" 6146, 6146A or 6146B.

    Every one for sale is either used or "new old stock" (supposedly unused, still in its carton from the factory, but probably manufactured 20 years ago).

    As such, unfortunately, they're all suspect.

    The good news is there were so many millions of them made over the years that a lot in circulation are perfectly fine.
     
  8. KP4SX

    KP4SX Premium Subscriber QRZ Page

    A tester may or may not pick up a problem. Whole different set of parameters being applied in a tester. Do like TRF says and pull the tubes and see if the fuse still blows.
    You're using the correct rating, right?
    Put your old tubes back in for a test to see if it still blows. Then replace one at a time.
     
    WQ4G likes this.
  9. W1RLP

    W1RLP Ham Member QRZ Page

    Thanks can I removed both finals then reinstall them one at a time and see if the fuse blows. I didn't have this problem before I installed the new tubes.
     
  10. K7TRF

    K7TRF Premium Subscriber QRZ Page

    I’d have to look at the schematic but I’m pretty sure the final tube filaments are wired in series so you can’t really run one at a time.
     

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