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Allen Type 1000-4 Amplifier for T12-A - Output Transistor Configuration

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  • Allen Type 1000-4 Amplifier for T12-A - Output Transistor Configuration

    Regarding the two output transistors on an Allen type 1000-4 Amplifier (T12-A organ):

    1. They are both Delco 305783 transistors, TO-3 package. I believe they are PNP germanium types? They don't measure cleanly with an ohmmeter and I haven't found any cross-reference data.

    2. The collector of one of them is insulated from the chassis (greased mica). The collector of the other is attached directly to the chassis (via an aluminum(steel?) mounting plate), using no insulator. Is this right?
    2a. Regarding the chassis-attached collector: the aluminum plate on which it is mounted isn't making a solid electrical connection with the chassis. I want to be sure that the collector really should be grounded before proceeding.

    I contacted Allen, looking for schematics - no luck.

    I've deconstructed the circuit far enough to know that neither collector should be grounded. Oddly enough, the organ has worked fine (well, almost) up to this point. I've been giving the organ a post-purchase shakedown.

    Thank you for your help.
    Chuck Bell
    Last edited by clebell; 10-11-2016, 08:51 AM. Reason: New info:
    ... I ask thee not to beware of Starbuck; thou wouldst but laugh; but let Ahab beware of Ahab; beware of thyself, old man.

  • #2
    The output power transistors on a T-50 amplifier used in the T12-A were 2N2289.
    I don't know what a type 1000-4 amplifier is.



    • #3
      I was reading from a paper label on the chassis top, underneath the expression capacitor: "No. 17,677 Type 1000-4 100 watts... Allen Organ Company".
      There is, however, a large 50 printed on the chassis where the power cord enters. I suspect that means T-50.

      That explains why I found zero search results for "Allen type 1000-4".

      Thanks for your help. I'm reverse-engineering an Allen T12-A for refurbishment/upgrade. The cabinet and manuals are in great shape. I figure that a service manual will become available on ebay - after - I've finished the work. It doesn't matter, though. I'm retired and this is interesting work.

      Chuck Bell
      An elderly Hammond organ repairman - still has almost half of his wits.
      Free to a good home.
      ... I ask thee not to beware of Starbuck; thou wouldst but laugh; but let Ahab beware of Ahab; beware of thyself, old man.


      • #4
        I think my question relates to this thread, but it may not . . . . . . .
        I have a T12-A that I purchased from the original owner about two years ago. My son plays the organ at church and uses this for practice at home.
        First, let me say that this organ is an engineering marvel and is very well made. I assume the vintage is 50's or 60's. It worked perfectly when I first brought it home and I don't think it had much maintenance done over the years.
        The organ has three speakers: fixed woofer, fixed mid-range (6-8"?), and a mid-range gyro speaker (6-8"?). Recently, the gyro speaker is not producing sound. It's not an issue with the brushes on the axle. The wires have continuity. I even unplugged the motor and jumped the base to the speaker to bypass the brushes and axle, but still no sound and no voltage at the speaker. Since the other speakers are still producing sound, I assume the amp is fine. I cannot find any loose wires or connections. Can you provide any information on how to trace the output to the gyro speaker? I absolutely LOVE this old organ and want to keep it going.

        Side note, I think the gyro unit still has the original V-belt. It's just amazing to think of the engineering and build-time it took to manufacture these organs.