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Safe to test tubes with plate cap off?

Discussion in 'Amplifiers' started by 357, Jun 18, 2018.

  1. 357

    357 Walkin' the dog

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    I want to burn-in some 572b's in my fl2100 to burn off ant gasses and then test them.
    Will it hurt them to do this with the plate caps off?
    I was told that amps like the 300a this is not a good idea. Something about cathode current.

    Anyone know for sure?



    thanks
     
    Shadetree Mechanic likes this.

  2. 357

    357 Walkin' the dog

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    Well I pulled the 850V wire off the diode board and insulated it safely.

    Time to bake a cake!

    IMG_3151.JPG IMG_3150.JPG
     
  3. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    Not sure if just filament heat is enough to getter the tubes. A nice carrier making the plates glow a dull red usually works just don't run them too bright orange. If the plates are the same colour as the filaments you have gone too far. :LOL:
     
    357 and Shadetree Mechanic like this.
  4. 357

    357 Walkin' the dog

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    What I'm seeing is a bit of blue plasma or something right at the anode bridge.


    IMG_3152.JPG IMG_3154.JPG


    I keyed the amp to check the idle current and the blue has gone.
    Seeing just under 100ma
     
  5. 357

    357 Walkin' the dog

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    When I key the glow comes back.
     
  6. 357

    357 Walkin' the dog

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    OK I tuned it at 20w in and waited keydown and seen a dark dark glow.
    300w with 20 in.
    I'm thinking these are pretty good.

    1973, maybe older, better

    IMG_2401.jpg
     
    Shadetree Mechanic likes this.
  7. 357

    357 Walkin' the dog

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    650 and change with 100w.
    These tubes seem to behave better, my other set see's over 700w but they dont like to dip at full output.
    These older tubes do dip at full output and draw only 400-450ma.

    Just wanted to make sure they do indeed work.
     
  8. 357

    357 Walkin' the dog

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    Looks like they are waking up

    IMG_3155.JPG IMG_3156.JPG
     
  9. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    Those 572B's don't like to make anymore than about 600 watts in that amp if you want them to last.
     
    357 likes this.
  10. 357

    357 Walkin' the dog

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    Roger that.
    I was just doing quick keydowns just to see.
    I'd say the tubes are good, now I can sell them and say they are tested.
    I think I will keep these though and sell the '77 roundies.

    As for the plate cap on or off I'd strongly suggest on and remove the HV lead.
    Theres not enough room to have them off
     
    #10 357, Jun 21, 2018
    Last edited: Jun 21, 2018

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