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Random tube question

Discussion in 'Amps and Cabs [BG]' started by i_got_a_mohawk, Aug 10, 2005.


  1. should tubes be completelly silver on the top end, i just noticed one half of one of my 6550's is pretty transparent :eyebrow:
     
  2. What you are referring to is called the getter flash, which is a disc fired during the tube's construction to burn off the excess gas left after the envelope has been pumped down. The location of the silver depends entirely on the manufacturer. If you notice that it is fading away to light brown or turning milky white, you've either got a leaky tube or your amp is biased DANGEROUSLY low. That would also account for the hum you are experienced.
     
  3. It depends on the manufacturer - from memory it has something to do with the process of creating the best possible vacuum inside the tube. I don't think it's an indication of tube performance.
     
  4. right cheers, its not milky white or brown (as ive seen when the getter oxidises)

    I just noticed it today, its really wierd, especially seeing how its only over one side of the 6550, the other half and the other 5 are fine

    Yeah, i think i may avoid firing my amp up right now, i think ill wait til a tech bias's it!

    Pic:

    [​IMG]

    I took it out to have a closer look, and the metal base is a bit loose :'( , so it could be some leackage :'( :bawl:
     
  5. BurningSkies

    BurningSkies CRAZY BALDHEAD

    Feb 20, 2005
    Seweracuse, NY
    Yeah, I'd be careful with that right now...beyond the buzz, and odd tube coloration, the loose base is bad mojo. Check the other tubes while you're at it. Sounds like it's time for a new set...and I wouldn't trust the ones you've got in it if their from the same bunch and same era as the damaged one. I'd coil up that power cord and make sure it doesn't go near an outlet.
     
  6. It does look like it's burning away to me.

    Yep.

    The base is just connected OUTSIDE through the pins. It doesn't help hold the vacuum at all. If you could see the tube 'naked', it would look like an oblong egg shape with wires dangling out of it. I'm still guessing you're burning up the tube with too little bias, not a leak.
     
  7. right, thats ok then, im sure i saw some tubes about that had the base heated onto the glass, well, the glassheated about it, so the loose base would have more than likely made slight fractures, not with these i take, so thats good

    it'll get bias'd next week, is that tube too far gone to save?
     
  8. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    Can't tell from the picture, its a bit fuzzy....

    But, it DOES look on the left as if there is a "haze" of "formerly known as a getter" material. Better focus (sorry) would help.

    Not all tubes are symmetrical as to the "getter".

    And some getter action does not mean the tube is dead. So long as there is a considerable amount of getter left, it may be fine.

    After all, the getter is supposed to remove active gases from the tube. But if there is leakage, there are inert gases also present, which eventually foul up the tube operation, and are not grabbed by the getter very fast, if at all (they may be ionized by tube operation, and then the getter may be able to 'get" them).

    And, the getter has a tendency to flake off and travel around when it has thoroughly done its work (normally only in a very leaky tube).

    Getters are not the only things that can be bad, but they are one of the most visually obvious faults when bad.
     
  9. Yeah, its definatly like a haze, with small patches, like i said, its sorta semi transparent

    aslong as the tube will be fine once its bias'd then its ok, or could there be a problem that isnt visible (which was also caused by what fooked the getter? )
     
  10. Here's possibly a more in focus picture

    It doesnt seem as bad, its a hard thing to take a pic off, because no matter what the glass on the outside is glossy

    [​IMG]

    it does look worse than it shows up in that pic tho