tubes getting gassy over long term storage

Discussion in 'Amateur Radio Amplifiers' started by KA5ROW, Oct 28, 2017.

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  1. KB4QAA

    KB4QAA XML Subscriber QRZ Page

    Phosphor compounds. I did the same thing. Got old TV's for parts from my neighbor who owned "THE" stereo/radio/TV shop in my town.
     
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  2. KB4QAA

    KB4QAA XML Subscriber QRZ Page

    Because nobody expected them to be stored for 60+ years. Some military tubes were stored and shipped in sealed cans/cardboard shipping tubes, but this had nothing to do with seal leakage.
     
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  3. WA7PRC

    WA7PRC Ham Member QRZ Page

    Probably, to keep the tube in a controlled environment to minimize external contamination... oxidation, etc. The packing material and outer can minimizes mechanical damage.
     
  4. AF7XT

    AF7XT Ham Member QRZ Page

    Glass and metal have different expansion and contraction curves in response to heating and cooling.
    Nature abhors a vacuum. The entire universe as we know it will relentlessly penetrate any vacuum vessel through any means available.
    The boundary between the metal used to go through the glass and the glass is not "perfect".
    The metal alloy selected to be in contact with the glass to form a seal has properties of expansion and cooling closely matching the glass.
    The metal used within the tube is electrically specific to the task.
    The metal use for the external pins is specifically chosen for ease of manufacture, temperature, and wear characteristics.
    These three different metals are spot welded within the tube and soldered or spot welded to the external pins.
    These spot welds are sometimes encapsulated within the glass seal.
    Even the vacuum of space is not completely empty.
     
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  5. W5THT

    W5THT Ham Member QRZ Page

    Tubes get "gassy" for two reasons. Obviously a leak of air into the tube is one - the other reason is because the chemical "adsorption" (bonding gas molecules to the sides of metal parts) slowly reverses if the metal parts are not hot enough to keep the gas molecules bonded to them. It is impossible to pull a perfect vacuum, there are gas molecules inside the metal parts that escape and can be recaptured by firing the "getter" after the tube is sealed. Some tubes use the plate as the getter and can be degassed by running them hot with LOW voltages that will not arc internally and damage the grids. Broadcast stations swapped big power tubes and used them to keep them from sitting too long and getting this problem. Details are in various places on the web. Just don't overheat the seals trying this.
    Pat W5THT
     
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  6. KA5ROW

    KA5ROW Premium Subscriber QRZ Page

    So how long to getter? with SSB you don't get there at all. What I do is get on AM lock the key for minute or two. let it cool, and then do it again let the tubes get real orange.
     
  7. KD5YPH

    KD5YPH Ham Member QRZ Page

    And what to do if in AM or CW with just a carrier one tube gets orange more quickly than the other?
     
  8. WB2GCR

    WB2GCR Ham Member QRZ Page

    If you've got a really gassy tube, one that might be saved, keydown with full HV and current will
    almost certainly arc the tube, fast. ie. running the plate orange.

    At least that's what I've been told...
     
  9. N5WVR

    N5WVR Ham Member QRZ Page

    That hasn't been my experience. On my SB-220, an extended SSB transmission at 60 watts exciter drive (which gives about 1 kw out PEP) will get the tube nice and orange.
     
  10. K1ZJH

    K1ZJH Ham Member QRZ Page

    Give the amp enough drive for the plates to show color with the amp slightly mistuned into a dummy load. Watch the grid current and keep the amp running just hard enough to show plate color.

    Of, get an RF speech processor and run some contests with some hard on air time.

    I have PL-175 and 4-400 tubes from the WHYN-AM transmitter which sat unused in my cellar since 1968. They tested fine last year. Same for a 3-500 that been stored since the mid 80s. Not all tubes go bad with time.
     

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