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Allen T12b speaker connection - Help

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  • Allen T12b speaker connection - Help

    I have what I believe to be an old Allen T12b organ. It does not have cabinet speakers - and was connect to external speakers. I need to know how to correctly connect speakers to it. I did not know if it even worked - but after I got it home - I connected a speaker to the output on the AMP. One terminal ID'd as COM, an no ID on the other. I connected and it does work. However, I very quickly discovered that it was at full volume. A little more research and I found that I could turn down the volume from the front of the AMP - because the volume pedal was having no effect whatsoever. I looked at it - and it appears everything is connected electrically and mechanically. But it does not do anything - no crackling noises - nothing. I thought perhaps it could have to do with the way it was connected to the speaker. Maybe there is a different place you are supposed to connect to speakers?

    There was a little page of a note pad that came with the organ. It was hand-written: a crude diagram of a rectangle - with 4 dots linearly. To the left was ID'd as L and to the right ID'd as R. Each dot was ID'd with a color - left to right: Black, White, Brown, Red. I found a place on the bottom of the cabinet that corresponded to this diagram. Those colors of wires in that order - terminated - and there was a place with screws where you would connect wires to. I don't know if it has anything to do with speaker connections or not. But wonder why that diagram was in the old envelop that came with it. I checked those colored wires with a multimeter - and I got 14.5 V on the white and red, 0 on the black, and 0.2 or 0.3 on the brown (if I can remember correctly)

    I play organ every Sunday at church - and thought it would be a good practice organ for home - but I would like to get it going.
    Any help would be greatly appreciated.

  • #2
    No worries. You connected your speaker correctly. The other terminals you speak of were the control signals for a gyro cabinet, which is a specific type of Allen organ speaker cabinet with a variable speed motor driving a rotating baffle on which the speaker drivers are mounted. This makes for some great effects, but it is not essential for you to have a gyro in order to enjoy your T-12. So attach any kind of quality speaker to the terminals on the amp, as long as it can handle the organ frequencies well enough. Use a speaker with 8 ohm impedance, as a 4-ohm speaker might overload the small amp in a T-12, if it's an older one.

    AS to the pedal not affecting the volume, you will almost certainly find that the small lamp in the base of the expression pedal is burned out. On the side of the expression pedal you will see a black wire going into the middle of a round metallic thing about 3/4" in diameter. The other end of that wire is attached to a slider resistor, and it carries about 12 volts to power the small lamp. You can pry that metal think out of the side of the pedal, and you will see that it holds (or should be holding) a little lamp called a "57X" which is an old-fashioned automotive lamp that you can probably get in an auto parts store. It will be simply called a "57" lamp. Allen specified that there should be a black or white paint dot on the end of the lamp to diffuse the light on its way to the LDR expression device in the other end of the assembly, but that is not absolutely necessary. so get a new lamp and put it in the holder and you should have proper expression control.

    Good luck!
    John
    ----------
    *** Please post your questions about technical service or repair matters ON THE FORUM. Do not send your questions to me or another member by private message. Information shared is for the benefit of the entire organ community, but other folks will not be helped by information we exchange in private messages!

    https://www.facebook.com/pages/Birds...97551893588434

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    • #3
      Wow! Thanks. This was much help. I connected to an old AMP - which had an 8 ohm speaker. I connected speaker wire to the organ's terminals - and put alligator clips on the other end - and connected those to the AMP speaker (without plugging up the AMP - basically just using the speaker). I actually had one of those bulbs out in the garage. I put it in - and now works great! I'm amazed at how well it works - considering how old it is.

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      • #4
        Be sure to disconnect that amp speaker from its own amp. Otherwise, you are loading down the Allen amp by having its current partly drained away by the output devices of the other amp. Clip one of the leads or otherwise unhook that speaker. The other amp might be presenting a low ohm load to the Allen amp, which might eventually damage it.
        John
        ----------
        *** Please post your questions about technical service or repair matters ON THE FORUM. Do not send your questions to me or another member by private message. Information shared is for the benefit of the entire organ community, but other folks will not be helped by information we exchange in private messages!

        https://www.facebook.com/pages/Birds...97551893588434

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        • #5
          Too Late! I did not realize that. I could have easily unplugged the speaker from the amp itself - but now I know what happened. It stopped making sound. I checked everything out and determined the organ amp was not longer working. It did just what you said. So I think I killed the organ amp. It has a red reset button on the organ amp - but it did not come back to life after pressing it. Is there any way of connecting the output to another amp? The only thing going into the amp is what looks to be a small coaxial cable. It runs from this junction box where it looks to be a white wire, and another wire wrapped in brass or copper....just those 2 wires into the coaxial cable.

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          • #6
            Oh dear. Another one bites the dust. That's quite tragic, because the Allen amp has certain characteristics such as input sensitivity and impedance that are unlike any other amplifier you can buy. But don't beat yourself up, because the old T-50 amps seem to be dying all around us. More than one forum member has had one quit recently, and I have some dead ones in the shop from years ago. They are quite fragile compared to modern amps, and especially since they are so old now.

            You can connect the RCA cable that goes into that amp to the input of some other amp and get some sound. Try the amp/speaker you were using to see if it will work. If not, a good powered box mixer can be bought for around $100 that will do the job. An input designed to accept a MICROPHONE will probably have about the right sensitivity. An input designed for connecting a CD player or keyboard or other line-level device will probably not give you enough volume.

            NOTE: The input impedance of all modern equipment such as most guitar amps and other such devices is too low, and the side effect is that the EXPRESSION will no longer function when these are connected to an older Allen organ.

            To remedy this, you must insert a 22k resistor in series with the input signal. In other words, connect the inner wire of the signal cable to a 22K resistor, then connect the other end of the resistor to the inner wire of the extension cable you are adding to go on out to your new amp. Don't forget to connect the ground (shield) of the existing audio cable to the shield of your new wire.

            That should work. But it's too bad the old T-50 is gone. Just take a lesson though. NEVER connect the output of an amplifier to any speaker that is already connected to the output of another amp!

            BTW, you should look underneath the T-50 to see if it has a couple of hidden fuses. You could try replacing them to see if that makes it work. It might, but chances are slim.
            John
            ----------
            *** Please post your questions about technical service or repair matters ON THE FORUM. Do not send your questions to me or another member by private message. Information shared is for the benefit of the entire organ community, but other folks will not be helped by information we exchange in private messages!

            https://www.facebook.com/pages/Birds...97551893588434

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            • #7
              I will check for any fuses, but I feel it is not likely. It has the reset button, just like on the power supply, but it did nothing. But I will look into and see. And if not - I will try the 22k resistor, etc. and see how it works

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              • #8
                I am going too get a 22K ohm resistor to connect and try that......but what wattage? I was looking for 22K resistors - but see they are listed for different wattage. Does it matter?

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                • #9
                  1/4 watt is fine. Even 1/8 watt is fine, as there is not any actual "power" being passed through the signal cable at that point.
                  John
                  ----------
                  *** Please post your questions about technical service or repair matters ON THE FORUM. Do not send your questions to me or another member by private message. Information shared is for the benefit of the entire organ community, but other folks will not be helped by information we exchange in private messages!

                  https://www.facebook.com/pages/Birds...97551893588434

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                  • #10
                    I removed the amp - just to see if there was anything visual about the damage.....to my surprise - there were 2 of those old glass fuses in there - both blown. I went and got replacement fuses - and now it works fine! So the old amp was not lost - still going!

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                    • #11
                      That's great! You are very lucky. Others who have had T-50 amps go out were not so lucky. Just remember not to connect more than one speaker to it, and never forget that you can't have two amps connected to the same speaker.
                      John
                      ----------
                      *** Please post your questions about technical service or repair matters ON THE FORUM. Do not send your questions to me or another member by private message. Information shared is for the benefit of the entire organ community, but other folks will not be helped by information we exchange in private messages!

                      https://www.facebook.com/pages/Birds...97551893588434

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