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Colored dots on Allen Organ tubes?

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  • Colored dots on Allen Organ tubes?

    I picked up an Allen Rondo the other day. Circa 1958 or so. Beautifully made under the hood, 5 octaves, 24 pedals, but flutes only, and not working so well. Heavy!

    It's got a pretty interesting rotating vertical speaker disk with two speakers on it facing out the front. Funny thing is, only one of the two speakers was ever wired up. The other is just going along for the ride (ballast, or manufacturing error?). From what I could hear with weak volume and a lot of the tabs doing nothing, the rotating speaker made a pretty pleasant vibrato. Not Leslie, but pleasant vibrato. Steampunk vibrato?

    It's got a pretty cool independent mono-block amp in it, coke bottle 6L6 pair, made by Webster Electric. There is a whole rack of oscillators, Sylvania 6SN7GTB's. All but one of the tubes look original. Two funny things about them. Some are taller than others, and they all (except the one that was replaced with a Westinghouse) have colored dots that look hand painted on the top. The dots are not all the same color. I'm looking at a few that I rinsed the schmutz off of, one has a green dot in the center of the top, and two yellow dots on either side. One (apparently the same tube but without the batch number on the top, has an orange dot in the center, with what looks like yellow and tan dots on either side. Another one, the insides look the same, but the glass is taller, different batch number, and it has some dots on the top, closer together, all three dots look brown.

    Anybody know what these dots were all about?

    Thanks in advance.
    Marty

  • #2
    The speakers are not incorrectly wired on that "gyro" baffle. They did indeed have the second one for "ballast" or balance. Easiest way to be sure the gyro wouldn't jump up and down when in motion! If both speakers were playing, the vibrato effect would be diminished. It is the movement of the sound source around the circle that produces the throbbing vibrato.

    The color dots on the tubes are probably placed there in factory testing, as tubes were pre-checked for various characteristics. I was not a tech back that long ago, but I do know that in the transistor era many manufacturers marked the tops of transistors with colored dots to indicate their performance in certain tests, and thus which parts of the circuit they were suitable for.

    As to the many tabs that seem to do nothing -- with the Allen "all flute" models, some tabs actually turn on a great many separate pitches at once to simulate certain organ tone colors. So, for example, if this organ has a tab marked "string diapason" and you turn that one one, it literally activates ALL the available pitches in the entire division. So, once that tab is on, nothing else can be added to it, and all the rest of the tabs will seem to be "dead."
    John
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