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Ameritron AL80-B blowing fuse on power up

Discussion in 'Amplifiers' started by mattsowders1989, Nov 8, 2017.

  1. BlowinSmoke

    BlowinSmoke
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    Can you give a make and model number of the tube tester you used to test a 3-500z. Thanks. Now that we are beyond the tube being bad the next step would be to "at least" check the rectifier diodes and see if there is a shorted one. Very easy to do. Then the HV secondary can be easily isolated from the rectifier and then once again see if the fuse blows. If it does then probably a transformer short if not then probably a capacitor.


     

  2. Captain Kilowatt

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    Just curious what kind of tube tester you used to check the tube. I don't recall ever seeing one that would allow a 3-500Z to be tested. Usually they are for much smaller tubes. The filament alone requires 15 amps of current. Then again I have not seen every tube tester ever made.
     
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  3. wavrider

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    Only 3-500Z tube tester I have used was a one tube amplifier with fuse in the HV line in case the tube arced over it would blow the fuse instead of taking out the ps.
     
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  4. BlowinSmoke

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    Well only partially true. Open filament is the only sure test for a meter and maybe if the tube has a hard G-F short, but most G-F shorts more often than not, won’t show on a meter. This is because most G-F shorts only show up when the filament is heated and migrates ( moves) and touches the grid or vice versa. Nor will a meter pick up a gassy tube that will arc and blow up unprotected parts. You may be lucky to pick up a short with a meter if you affix the meter leads to the tube pins and slowly roll the tube on a flat surface. An analog meter works best.
     
  5. nomadradio

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    Intermittent G-K shorts are where the "octopus" 2-terminal curve tracer/component tester really pays for itself. Even a brief contact between a loose grid wire and the filament will 'flip' the trace on the 'scope screen.

    Probably the most insidious thing to go wrong with a 3-500Z, and way too common. The control grid is a cylindrical "fence" of parallel vertical wires held in place by a wire ring at the top, bottom and middle of the structure. When the spot weld holding one end of a grid wire comes loose from the ring at that end, no problem occurs until heat warps the wire. The loose end will "curl" away from the broken weld spot until it touches the filament, or worse, the anode.

    Driving the tube too hard, or loading the output too tightly can push grid current high enough to overheat the grid and break one of the spot welds.

    Our routine test before we'll power up a 3-500Z in the customer's equipment is to hook the octopus from one cathode to one grid pin and (gently) slap the tube on the side, turning it right-side up, upside-down and sideways. Any flash of movement on the 'scope screen means that tube will be toxic to the amplifier sooner or later.


    73
     
  6. wavrider

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    The old octopus to o scope, I remember way back in the early 80s I was a young pup in the navy electronic field, we built octopus to use testing components.
    those were the days.
     
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  7. Tallman

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    My primary Oscilloscope came with one built in.
    [​IMG]
     
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  8. Tallman

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    I had one employer right after I got out tell me that if I wasn't Navy he would not even bother talking to me to hire for his spot. He said Navy techs are the best. I think I have to agree! But of course I could be a little biased.
     
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  9. nomadradio

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    The guy who introduced me to this toy was Marine Corps.

    73
     
  10. wavrider

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    Marines attend navy schools;););)
     
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  11. wavrider

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    http://www.jammarcade.net/simple-component-tester-a-k-a-octopus-curve-tracer/

    If I remember correctly the octopus was actually in a Rate training manual for third class Petty Officer..Few years later the Navy was purchasing a signal tracer, octopus in a box with CRT.

    Few years after that we were tracing circuit cards,(mapping the circuits) on known good working CCA's ( circuit card assemblies) saving them to floppy disk ( showing my age here) and calling them gold disks.
    Then we could compare the gold disk to a suspected bad CCA and trouble shoot using the circuit tracer.

    Sort of taking the TECH out of technician and using computers to compare results.
    This system was called acronym,,,ATS or Automated Test system, big huge Texas instrument main frame.

    The 2M microminature repair techs ( interpret as solder techs) said the new system was just throwing parts at the problem and the technicians forgot how to trouble shoot, were only changing the components the computer program suggested and not verifying the componenet was actually bad.
     
  12. Tallman

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    I had a Marine on board my ship that was always giving me hell about being a Swabby.
    He had a purple heart that was awarded during one tour in Viet Nam.
    I asked him when he was injured and they called for a medic, who showed up?
    A Navy Corpsman is who showed up, a swabby!
    End of harassment.
    This was my ship. AD-36 Destroyer tender. Perfect ship for learning everything about everything. We repaired everything that communicated or radiated.
    [​IMG]
     
    #27 Tallman, Nov 12, 2017
    Last edited: Nov 12, 2017
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  13. wavrider

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    We had the marines on aircraft carriers and security when I first entered the service.
    Called them Mardet, Marine Detachment.
    Sea going bell hops was our nicknames for them.
    Great bunch of guys.
    We snuck into their berthing compartment and stole their chrome floor buffer.
    Hung it from the overhead pipes on the mess decks.
    Those jar heads were one pissed off bunch about that.
     
  14. Tallman

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    The War Cry of the Coast Guard was, "Let's go to the beach!"
    This is a little jab at one of my relatives. He was moaning and carrying on about how tough the commute home was every night. Poor baby!
     
    #29 Tallman, Nov 12, 2017
    Last edited: Nov 12, 2017
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  15. wavrider

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    I cruised on aircraft carriers.
    USS John C, Stennis, USS Eisenhower. USS John F Kennedy. USS Saratoga
    I know what you mean by repairing everything. We had an AIMD similar to the black shoes SIMA.
    AIMD afloat and we repaired all the small boys and tin can comm equipment or radar while forward deployed.

    Got my first introduction to HF data link.Got hooked on BIG HF amps at an early age.
    Those ET's and RM's got some fun stuff in the communications room.
    And a lot of tubes laying around , pulls from PM schedules.:):)
     
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