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Thread: help plz: identifying old tubes

  1. #1
    Junior Member
    Join Date
    Nov 2010

    help plz: identifying old tubes

    A friend found out I was reading up on building a tube amp and gave me a handful of tubes that he found in an old garage. Apparently they were pulled from an old radio. All 5 have the same approximate shape (like this sovtek kt88 - Google Search).

    1 - 8 pins, says "IC7G Made in Canada" (maybe "1C7G"?) on glass, has metal "nipple" on top, plastic base says "General Electric Radiotron, Licensed by Thermionics Ltd."

    2 - 7 pins, says "1D5G Made in Canada", nipple, same GE statement on base

    3 - 6 pins, "IFG" on glass (could be "1F6"), nipple, "Rogers" on base

    4 - 4 pins, "30" on glass (could be "3O"), no nipple, "Westinghouse Radiotron, Licensed by Thermionics Ltd, Patented 1923-1940"

    5 - 6 pins, nothing on glass, no nipple, same Westinghouse statement but patent dates are 1924-1941

    Do these descriptions ring a bell with anyone?

  2. #2
    Supporting Member Jazz P Bass's Avatar
    Join Date
    Dec 2008
    Wernersville, PA
    Certainly are radio tubes.
    1C7G is a pentagrid converter
    1D5G is a remote cutoff pentode
    1F6 is a duo-diode\ pentode in one tube
    The others I cannot help with.
    Tube Data Link: electron Tube Data sheets - Search

  3. #3
    Senior Member
    Join Date
    Dec 2008
    Type 30 is an old-style medium-mu triode with a UX-4 base.

    Can't really help with the last one. No markings makes it difficult, to say the least... Now, if you knew the radio they were from, you could do it by process of elimination :-)

  4. #4
    Junior Member
    Join Date
    Nov 2010
    Thanks folks, much appreciated!

  5. #5
    Junior Member TubeType's Avatar
    Join Date
    May 2010
    Southern Indiana

    An Old Trick

    Rule 1: Never clean an old vacuum tube's glass envelope before attempting to read its number. You might wash it off.

    With that said, here's an old trick I learned, in my earlier days, that may help you display your invisible vacuum tube number.

    1. Place the vacuum tube into the refrigerator for about five minutes.

    2. Remove the vacuum tube from the refrigerator. Do not touch the glass envelope with your fingers.

    3. Slowly exhale a breath or two onto the cold vacuum tube's glass envelope. The surface of the vacuum tube will become cloudy.

    4. Hold the vacuum tube at a slight angle in the light and look for a very faint vacuum tube number.

    Note: This trick is a last resort and does not work every time.

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