Tubes Asylum

Small signal tubes and the nipple on top .....................

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OK - Here is a simpleton question. - Why do most all small signal tubes like the 12AX7, 12AT7, 6922 etc. have a nipple on the top of tube? - And Power tubes like the KT88, 6550 or other tubes like the 6SN7 do not?
I assume that it has something to do with the manufacturing process, but maybe someone has a good answer for this.
As adnut would say - Just wondering?

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Kimber Kable

Re: Small signal tubes and the nipple on top ..................... - Eli Duttman 15:51:04 07/19/02 (5)
It has a lot to do with the basing. The minature tubes use a glass button base that is an integral part of the envelope. Octal based tubes use a base that is cemented to the envelope; the connections to the base come through a stem and are soldered to the pins.
BTW, the EI KT90s that I use in my H/K Citation II and the EI 6CA7s use a plastic button base and have the nipple on top. The KT90 looks like an EL84 that's been taking LOTS of anabolic steroids.

Eli D.
- Vacuum tap - steven oda 19:30:02 07/19/02 (4)
  CT & Eli,
  I think that the teat is the point where the vacuum is applied to the bottle once it is sealed. The tap is then closed off by quick application of a flame or high heat.
  Nine-pin minis have the vacuum tap at the top. Eight pin octets seem to have the tap at the bottom. It's teat is hidden by the plastic or metal base and the centering pin.
  Final high vacuum is achieved by the metal coatings applied to the getter ring or cup. The blast sucks up most remaining O2---at traps it as stable oxides.
  - Re: Vacuum tap - OLLY 06:22:46 07/20/02 (3)
    Very interesting all that but it does not explain why half of my 7868's have a smooth top and the other half have the vaccuum nipple on thev top. "VEERRY INTERESTING".
    OLLY
    - Re: Vacuum tap - steven oda 08:47:42 07/20/02 (2)
      Looy,
      The one without vacuum nipples at the top, may have them at the bottom. The base night be hiding the little teat.
      - Re: Vacuum tap - OLLY 19:25:02 07/20/02 (1)
        
        In Reply to: Re: Vacuum tap posted by steven oda on July 20, 2002 at 08:47:42:
        
        The 7868's do not have a base and sure enough the nipple is on thr base between the pins. You would think that with these valves that were not made by many manufacturers that they would be identical. Maybe the idea was to distinguish between makers so they made them different. Any ideas out there as to who made the 7868's apart from RCA as the smooth tops have the RCA brand on them and I cannot see anything on the others.
        OLLY
        
        Novar WAG - steven oda 23:06:12 07/22/02 (0)
        
        In Reply to: Re: Vacuum tap posted by OLLY on July 20, 2002 at 19:25:02:
        
        Olly,
        Maybe some 7868 were sub-contracted out to GE. Seems to me, I may have seen glass bottom 7868, a long time ago, with nipples on the bottom---and GE logo.

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