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Thread: A-100 few issues vibrato, bleeding note, internal speaker help

  1. #1
    ppp Pianississmo rorganman's Avatar
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    A-100 few issues vibrato, bleeding note, internal speaker help

    I recently purchased an a100 organ with a leslie 702 tone cabinet. I installed a trek crossover, and connected the leslie using cat 5 cable(ethernet) . The organ had a few issues but i didn't mind as i only paid 100 for the organ and 250 for the speaker.

    One issue was that the tone wheels was seized up, i fixed it by oiling it over a few days. ONce i got it to spin freely i noticed a few other problems .
    The vibrato was motor boating at first and then is suddenly became almost in audible i was thinking it was from over oiling, but i removed it a took it apart somewhat and wiped away the little oil i could find. I then reinstalled it and the problem still persists. I am thinking it may be resistor or something going on with the actual circuit for the vibrato channel note sure what to isolate or how to test.

    Another problem is the c5# note seems to have vibrato or an extra shaky harmonic if i pull out the third draw bar. it changes to a different c sharp note and sometimes eb depending on which drawbar or combination of draw bars i pull. Im not sire whether it is a filter, capacitor or a tone-wheel issue.

    my final problem is that Im trying to figure out a way to cut the internal speaker off and on. I was thinking of taking one side of the main output wire from the amp and running it through a potentiometer before it reaches the speakers.That way i could adjust the level/mix or cut it off all together. Is this possible? any other solutions>

  2. #2
    mp Mezzo-Piano Jaim's Avatar
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    Vibrato - If you went from motor boating to none - possible shorted wires somewhere. But with this being "new" organ I would basically start over on the Vibrato troubleshooting. I would check the output of the preamp vibrato circuit on term C (brown wire running to vib line box). Hold a key down - 8" DB at 8. With a meter set on AC, should read about 5.4 VAC on term C to ground. If that's ok - then problem lies in the line box, switches or scanner.

    C5# - identify the tone number using the chart at: http://www.dairiki.org/hammond/wiring/
    Tonewheel flutter can be caused by a stuck tonewheel clutch.

    AO39 amp cutoff options:

    1. Pull rectifier tube
    2. Slight AO39 rewire and add power switch.
    3. MEE kit.
    4. Pot on speaker.

    I've done 1, 2 & 3.

    Jim

  3. #3
    ppp Pianississmo rorganman's Avatar
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    Thanks a million, i will try this tonight and let you know what i come up with.

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    ppp Pianississmo rorganman's Avatar
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    Update A-100 vibrato, bleeding note, internal speaker

    update 6/18.

    i was finally able to successfully add a volume pot and control the internal speaker volume. however i think it has the wrong resistance range because i only get volume variance between the 9 and 10 position from zero to 9 there is no volume.And the transition between 9 and 10 is very abrupt.Any suggestions?

    Also, i used the filter chart you provided and added oil directly to the appropriate gears and notice some improvement.

    More importantly, when i when to test the level improvement, I noticed that the vibrato was suddenly working, and the volume was back to normal but it was motor boating. I played around with it for a couple minutes and then the volume started to fade until it was barely audible. I then cut the organ off and came back to it several hours later, and the vibrato was working again , still motor boating, but the volume was normal . After a minute so, the volume started to slowly fade until it was again inaudible. Any thoughts? Suggestions?

    - - - Updated - - -

    update 6/18.

    i was finally able to successfully add a volume pot and control the internal speaker volume. however i think it has the wrong resistance range because i only get volume variance between the 9 and 10 position from zero to 9 there is no volume.And the transition between 9 and 10 is very abrupt.Any suggestions?

    Also, i used the filter chart you provided and added oil directly to the appropriate gears and notice some improvement.

    More importantly, when i when to test the level improvement, I noticed that the vibrato was suddenly working, and the volume was back to normal but it was motor boating. I played around with it for a couple minutes and then the volume started to fade until it was barely audible. I then cut the organ off and came back to it several hours later, and the vibrato was working again , still motor boating, but the volume was normal . After a minute so, the volume started to slowly fade until it was again inaudible. Any thoughts? Suggestions?

  5. #5
    fff Fortississimo David Anderson's Avatar
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    Putting a regular pot on the speaker is a bad idea and should not have been recommended due to the fact that a tube amp needs to see the proper load. To cut power to the internal A-100 speakers, you need a component known as an L-pad rated for the full output of the amp (~15 Watts). Preferably, you would have a 4 Ohm L-pad, though these are hard to find.
    I'm David. 'Dave' is someone else's name.

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    ff Fortissimo enor's Avatar
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    Vibrato fading and dying after a while is due to some problem in the preamplifier; the motorboating is something within the scanner, delay line or wiring. You have several vibrato problems at once ... not uncommon, and not complicated.

  7. #7
    ff Fortissimo Tim_at_Jonas's Avatar
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    The place to put a pot is between the output of the preamp and the input of the main amp. It's a balanced line, so you'll need a dual pot, audio taper. 100k would do the job I think.

  8. #8
    ff Fortissimo enor's Avatar
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    Quote Originally Posted by Tim_at_Jonas View Post
    The place to put a pot is between the output of the preamp and the input of the main amp. It's a balanced line, so you'll need a dual pot, audio taper. 100k would do the job I think.
    Yeah but that would also drag down the signal to his Leslie.

    If the OP really wants a separate volume control for the internal speakers (rather than an on/off) there are 2 ways - both somewhat involved and expensive:

    * An L-pad big enough for the power that the internal amp puts out
    or
    * An extra audio transformer in the line between preamp and power amp, so that the preamp output goes directly to Leslie while the power amp is behind a transformer. That way you could do a standard dual pot volume control on the input of the power amp, without it dragging down the Leslie.

  9. #9
    ff Fortissimo Tim_at_Jonas's Avatar
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    I don't think it would have much of an effect. I don't know about a 702, but the Z in of a 122 is 120k, and connecting a second one does not seem to affect the organ's output level.

  10. #10
    ppp Pianississmo rorganman's Avatar
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    IMG_3386.jpg

    update July 2017.
    I was able to download the schematic. and isolate the vibrato channel and narrow down the issue to a few culprits. I tested the 6au6 tubes and 12bx... and they tested out fine.I then removed the pre-amp and saw the the 1 meg resistor was burnt and discolored as seen in the pics, I replaced the resistor but i still little to no volume when the vibrato is turned on. Any suggestions, Im out of answers.


    Concerning the volume control.
    I was able to purchase an l-pad however it is an 8 ohm 15 watt not 4 ohm. I was wondering if i could decrease the resistance by half by adding a resistor in series??? any suggestions?

    IMG_3115.jpgIMG_3385.jpg

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