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Expression lamp for Allen organ

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    Expression lamp for Allen organ

    As I reported in a separate thread, I got to church yesterday morning and found I had no expression on the great. Today I removed the back of the organ and the wire enclosure around the expression/crescendo area, then had to remove the four screws holding the swell pedal mounted, so I could move the swell away from the great shoe far enough to pry out the lamp holder.

    Since I was going to so much trouble, I decided to replace BOTH the great and swell shoe lamps, lest I find myself doing this same thing again right away. Both lamps appeared to be original (from 1991 or 92), and they were smaller than the typical type 57X lamps that we are so used to seeing in there. I'm not sure, but perhaps Allen actually changed over to a smaller lamp at some point and I just missed the memo. I couldn't find a number on the lamps, but it had the regular bayonet mounting like the #57, but the glass bulb was somewhat smaller. A small dot of white paint was applied to the tip, as usual.

    Measuring the one lamp that was still good, I got a reading of about 5.4 ohms resistance, exactly the same as a type 57 bulb, so I assume that even if this bulb is a different number, it has the same amp rating as the 57. And I have a box full of brand new #57 lamps, so I had little choice but to use them. They fit easily into the bayonet holders, and slipped right into the openings in the sides of the shoes.

    DOES THE WHITE DOT MATTER? That has been a question posed here. I usually say don't worry about it. And today of course I didn't worry about it, because my box of lamps don't have the dot, and I don't really know how to put one on there. So I just used them right out of the box.

    When I turned on the organ, the expression worked, but the bar graph indicators went off with the shoe still about 1/4 open. That told me that the lamps were too bright, possibly because of the missing dot, or perhaps because of their slightly different shape.

    So I loosened the set screws on the slider resistors that control the lamp brightness (these are located right underneath the shoes), and set each one exactly halfway through its travel, just to see what would happen. (Before I moved them, they were set quite near the "bright" end of travel, nearest the terminal that receives the 12 volts from the 12 volt supply in the floor.)

    Walking around to the bench, I then observed that the expression indicators would not go completely off, but still had 2 or 3 segments lit when the shoe was in the closed position. Thus, the lamps were now too dim to do their job. So I went around to the back (I didn't have a helper today, which would've made this much simpler!) and moved the sliders just the slightest bit toward the hot terminal, then checked again and found that the expression indicators would go off right when I wanted them to, just as each shoe fully closed. I had it about right.

    If I'd had a helper, I could've had him or her watch the bar graph indicator, with the shoes closed, while I made small movements of the sliders, and just let me know the moment the last segment went out, then I'd know I had found the right spot. But I was doing it by trial and error, which happened to work out this time. But if you have a helper available, make use of him or her.

    The white dot, best I recall from my official days with Allen, was put there to make sure the expression curve would be smooth and even, without a sudden jump in volume at one end of the pedal travel. As far as I could tell, after I got the lamp brightness adjusted with the sliders, the curve was as smooth and even as it could be. There was definitely no abrupt change at either end of pedal travel.

    If you install a new lamp and then have that abrupt volume change, you might try turning down the lamp brightness considerably. It's easier to adjust on MDS and later models with the bar graph, but you can use your ears to adjust it correctly on other models.
    John
    ----------
    Church: Allen MDS-45 with Allen MIDI-DIVISION-II expander
    Home: Allen Renaissance R-230 with expanded four-channel audio and MIDI-DIVISION-II
    Shop: Bunch of organs in varying conditions, some good, some not...
    Half of an incredible two-man organ service team -- servicing all the major digitals in Arkansas churches
    https://www.facebook.com/pages/Birds...97551893588434

    #2
    The spot, it's black on my MOS-2 model pedals, is to mask the bulb's filament preventing it from shining directly on the LDR which would cause an abrupt change in volume when revealed. Allen could have accomplished the same thing by using a frosted bulb but the paint was probably cheaper. With the spot in place, the position of the resistor slider makes no difference in the smoothness of the expression control on my MOS-2 model. I can set it at either extreme and the pedal is still effective over its entire range. It's purpose seems to be to assure that multiple expression pedals track each other and behave the same.

    On my organ, there's a switch that makes one of the swell pedals a master. It does this by switching the control from one pedal to a LDR in the master pedal. For this to be practical the pedals need to track each other and the sliders facilitate this.

    Of course, things were a bit different in the MOS days. The expression pedal LDR was directly in the audio path so there was no A/D converter that could be maxed out before the end of pedal travel and there were no helpful indicator lights to indicate the pedal position that would require a precise adjustment of the sliders.
    -Admin

    Allen 965
    Zuma Group Midi Keyboard Encoder
    Zuma Group DM Midi Stop Controller
    Hauptwerk 4.2

    Comment


      #3
      Wondering whether the venerable 57X incandescent lamp will become as extinct as the DoDo Bird (so I'd better stock up), I wandered onto the O'Reilly Auto Parts web site since they have a store just two blocks from my house. I was amused to see the standard #57 and the long life #57 (both Sylvania and made in China) had the same spec for voltage, current and hours (500). Two long life #57 lamps were listed at a price of $5.49 - a lot more than I was expecting.
      Larry is my name; Allen is an organ brand name.

      Main: Allen RMWTHEA.3 with Rocky Mount Electra-Piano, Allen 423-C + Gyro cabinet, Britson Opus OEM38, Saville Series IV Opus 209, Steinway AR Duo-Art, Mills Violano Virtuoso with MIDI
      Lower Level: Hammond 9812H with roll player, Gulbransen Rialto, Roland E-200, Vintage Moog
      Shop: Mason&Hamlin AR Ampico piano, Allen ADC-5300-D with 18 speakers and MIDI, 4 Allen theater organ tone cabinets (including 3 Gyros, but don't call me Gyro Gearloose!).

      Comment


      • jbird604
        jbird604 commented
        Editing a comment
        That's a lot more than I paid for my last order of #57 bulbs. I don't think I paid more than a dollar apiece, but that was when buying 2 or 3 boxes of 10 each from Mouser or somewhere. One of these days they could become extinct as everybody quits making incandescent bulbs, but there are so many products out there with bayonet-style 12 volt lamps in them, they should be available somewhere as a legacy item. In the past, before I got aggressive and sought ought some #57 lamps on the internet, I'd just pick up almost any old lamp from Radio Shack or the auto parts store that had the standard bayonet mounting, then I'd adjust the brightness with the slider. I remember using a number 1891 lamp many times because it was always available at Radio Shack.

        BTW, the #57 is going to last far longer than 500 hours in an Allen expression shoe because it is being run at a lower voltage than the 12 or 14 volts for which it is rated. With the slider pulled back a bit, the voltage across the filament may be as little as 7 or 8 volts, which ought to extend the life of that lamp to perhaps thousands of hours. That's why you often find an Allen that is 30 years old and has never needed a new expression lamp.

      • Admin
        Admin commented
        Editing a comment
        These are still readily available on Amazon, 10 for under $8.00.
        https://amzn.to/2NU3aG3

        LED equivalents are also available at around a dollar each in quantities of 10
        https://amzn.to/2Na2OLX

      • D1gichip
        D1gichip commented
        Editing a comment
        I get plain #57 lamps and use black fingernail polish on the top of it. I've been doing that for many years. I get the lamps, paint the tip of them. When it dries, I put them in foam block with a thin foam rubber on top and they go in my parts drawer in my car. I always have a stock of them here. The black spot is to diffuse the light before it hits the slot in the pedal. I never have to mess with the voltage on the lamp this way.

      #4
      Well, maybe I'll wipe the black dot off and give that a shot on my ADC. My painted dot keeps flaking off no matter what I try. It lasts for a couple of months. I've been tempted to lightly sand the glass to get the paint to stick better. I've also thought of wedging a little disk of milk jug into the cavity to diffuse the bulb's light if the clear bulb is not smooth enough.
      Sam
      Home: Allen ADC-4500 Church: Allen MDS-5
      Files: Allen Tone Card (TC) Database, TC Info, TC Converter, TC Mixer, ADC TC SF2, and MOS TC SF2, ADC TC Cad/Rvt, MOS TC Cad/Rvt, Organ Database, Music Library, etc. PM for unlinked files.

      Comment


      • tucsondave
        tucsondave commented
        Editing a comment
        Try black fingernail polish.

      • samibe
        samibe commented
        Editing a comment
        I tried that the time before.

      • D1gichip
        D1gichip commented
        Editing a comment
        Use black fingernail polish. The black spot is very important.

      #5
      Admin is correct in saying that the dot is used to mask the filament from shining on the LDR. In later years, Allen redesigned the "birdhouses", as wee used to call them, and added a piece of plastic in the "birdhouse" to diffuse the light. Therefore the dot on the bulb was no longer needed. Since then, Allen changed to a control and eliminated the bulb and light cell in their expression pedals.

      Comment


      • you795a
        you795a commented
        Editing a comment
        The potentiometer is a Bourns continuous turn potentiometer. I am not sure of the rating any more. It has a blue housing. The pedal was totally redesigned as well. It is mounted from the top and from the front instead of the back. Allen dropped the LDR because supposedly they couldn't get them any longer.

      • jbird604
        jbird604 commented
        Editing a comment
        Oddly enough, a continuous-turn Bourns potentiometer is what Rodgers now uses (or what they send out as replacement pots for PDI and later organs -- I can't tell you what kind of control is used on the current crop of Johannus-built Rodgers organs). Back in the 50's Allen wanted to get away from using pots in the expression circuit because the expression pot was actually in the audio path, and when the pot became scratchy it caused noise in the audio. Nowadays, the expression control on any new organ simply sends a voltage to a digital control circuit, so a bit of irregularity in the carbon track isn't going to cause audio artifacts. I guess it was a wise move to abandon the lamp and cell, since the pots are pretty much guaranteed trouble-free for life.

      • you795a
        you795a commented
        Editing a comment
        Allen uses the same pot in the expression shoes as well as the crescendo shoe, just adjusted a little different., by maybe 2 gear teeth. One problem is that when the felt compresses in the closed position, it can cause the shoe to go full volume.

      #6
      Use caution if ordering the LED replacement lamps. Some LED's are not Dim-able, at a lower voltage they will simply shut off. And as Jbird mentioned the lamps typically in a Allen run at 7 - 8 volts, which might not be enough voltage to make the LED turn on. I am going to order from Amazon the #57 incandescent type for if/when I may need them for my Allen 705D
      74corvette
      Allen 705D
      1871 Estey Cottage Organ. ROS Reg#5627

      Comment


      • jbird604
        jbird604 commented
        Editing a comment
        Good comment. I think Allen owners should simply buy a few #57 lamps and put them in the bench in case they are needed one day and are not available. The brightness control is nothing but a wirewound slider resistor of about 50 ohms, and if the LED contains a dropping resistor of 1000 ohms or so (as most do), a slider resistor of merely 50 ohms is not going to affect the brightness to any appreciable extent. So there could be problems when using an LED for that reason, besides the fact that some are not rated for dimming.
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