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

  1. #11
    mp Mezzo-Piano Jaim's Avatar
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    The screen and plate resistors of the 6AU6's are prone to failure. I normally replace these. R7 & 8 and R19 & 20. You could confirm this by carefully measuring the DC voltage on pins 5 (plate) and 6 (screen) on V1 & 2.

    Jim

    ao28_under.jpg

  2. #12
    ppp Pianississmo rorganman's Avatar
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    Update I. Finally bit the bullet and had an organ tech come out. He replaced all the tubes. Checked the scanner by wetting his finger and touching the area near the top left with a series of capacitors, It is definitely scanning . He the stated that he had the problem narrowed down to an output issue,as you can hear the vibrato working just with very low volume.he asked if I check the output voltages per the schematic.i told him I didn't know where to check(I work on
    Computers for a living) ive been looking for some obvious output component but I'm not sure where to measure the +280,+290,100v etc .anyways,he never measured either.he assumed that was the 1.0 capacitor and charges $100 and left.he never came back.i replaced the capacitor my self,but still no change in the vibrato volume.help please.im even willing to do a google hang out or skype if anyone is willing

    - - - Updated - - -

    Update I. Finally bit the bullet and had an organ tech come out. He replaced all the tubes. Checked the scanner by wetting his finger and touching the area near the top left with a series of capacitors, It is definitely scanning . He the stated that he had the problem narrowed down to an output issue,as you can hear the vibrato working just with very low volume.he asked if I check the output voltages per the schematic.i told him I didn't know where to check(I work on
    Computers for a living) ive been looking for some obvious output component but I'm not sure where to measure the +280,+290,100v etc .anyways,he never measured either.he assumed that was the 1.0 capacitor and charges $100 and left.he never came back.i replaced the capacitor my self,but still no change in the vibrato volume.help please.im even willing to do a google hang out or skype if anyone is willing

  3. #13
    fff Fortississimo jdoc's Avatar
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    all the tubes was shooting in the dark, not troubleshooting, don't count on him!!!!!
    1956 M3, 51 Leslie Young Chang spinet, Korg Krome and Kronos

  4. #14
    ff Fortissimo enor's Avatar
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    Rule of thumb regarding Hammond console troubleshooting: It's not a tube.

  5. #15
    ff Fortissimo Tim_at_Jonas's Avatar
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    When I have had the volume issue you have described, it has been a cap or resistor.

  6. #16
    mp Mezzo-Piano Jaim's Avatar
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    Vibrato signal. From preamp terminal C - to line box - through the vib rotary switches - scanner and back in terminal D.

    Vib on, with a meter set on AC, read terminal C. Hold a chord - read 3-5 Volts AC. If you don't read that, then there is a issue around v2.

    Jim

  7. #17
    ppp Pianississmo rorganman's Avatar
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    Final Update Its working now

    Update-Sept 2017

    I finally got tired of swapping out resistors and went out and purchased a replacement amp. It came with new tubes and was rigged with an audio input and speak on power output. I'm assuming that they were using it a a lead guitar amp. At any rate. I unsoldered everything, then soldered to the new amp cut in on and nothing. Wiggled the audio cord and it worked but vibrato had the same issue. i put a water jug on the organ keys for weight and cut the vibrato on. At first there was nothing but then i wiggled a few wires (the brown wires) and it cam on loud with a ground hum. i then replaced the brown wire and resoldered every potential loose connection. Cut it on, and nothing. even worse i could not wiggle anything to get it to cut on. I was pretty much lost at that point, but my trouble shooting was leading me toward a ground issue. I then did some research an came across a procedure to fix motor boating. I read it close ly and it said that by zapping the unit, it would burn of excess oil that was causing a "ground issue"/. I disconnected the speakers, and hooked a wire from the #1 pin on the b12 tube and proceeded to zap every visible brass crew on the vibrato scanner. surprisingly it works like new now. I would have never figured that out by swapping resistor and reading the schematic

  8. #18
    mf Mezzo-Forte Roger Memphis's Avatar
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    Wow... Congrats, Rorganman! So, now I wonder if it was actually oil somewhere, or could it have been dendrites in the scanner?
    In any case, I'm glad you got it fixed... hope it sounds great.
    Cheers
    Roger Memphis
    C-3 with O-M, 145, 122RV, 2 PR-40's, PSR-36
    CV with HR-40, 2 B-40's

  9. #19
    ppp Pianississmo meter43's Avatar
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    On the choppy vibrato it is something in the line box. I would recap its about 2 dollars in parts and a couple hours labor. make sure there are no broken wires feed the line box. You can use a leslie half moon switch. Break the output from the G G terminal on the AO-28 preamp feed that to your switch then back to the amp. that's one position then the opposite position can feed a leslie and the middle position can feed both.
    One more thing swap the 12BH7 tubes on the preamp first and see if that does anything for your vibrato.

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