Announcement

Collapse
No announcement yet.

Sudden Volume Drop in M101

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

    Sudden Volume Drop in M101

    Was playing the M101 when suddenly the vibrato got very choppy, for just a few seconds, then the volume dropped to about 1/4.
    The volume pedal still works, but max volume is very low. Using the stock AO-29 amp.

    #2
    Is it the same if you cancel the vibrato?
    Current organs: AV, BC, A-100
    Current Leslies: 22H, 142, 147, 760
    Organs in the past: L-100 (several), M-100 (x2), T-100, E-100, CV
    Other keyboards: Roland FP-4, Yamaha DX7, Yamaha TX81Z, Yamaha Motif ES Rack, Korg Krome, Novation Mininova

    Comment


      #3
      Originally posted by enor View Post
      Is it the same if you cancel the vibrato?
      Ah. As you suspected, the full volume comes back when the Vibrato is off.
      What to do now?

      Comment


        #4
        Swap the position of the pair of 6AU6 tubes.Try those tubes in the adjacent sockets,V1 into V2,V2 into V1.
        One is the non vibrato channel,the other is the vibrato channel.The tube types are stamped into the metal in the front of the AO29 amp.
        6AU6 have a metal shield covers,the only 'pair' with covers(12AX7 isn't a pair)......
        We need to verify the tubes operate correctly,and at this point you have only one working correctly.
        If the vibrato channel starts working and the non vibrato doesn't after the tube swap, we have narrowed it down to at least a bad 6AU6 tube.
        Many times it is only a tube or dirty/shorted contact on a pin or socket that causes this issue.Seldom is it the tube,they lose volume usually before they totally give it up.
        sigpic A100/251 A100/147 A102/222 B2/147 BCV/122 M3/145 M102/145
        Various modern keyboards and modules.

        Comment


          #5
          Originally posted by Sweet Pete View Post
          Swap the position of the pair of 6AU6 tubes.Try those tubes in the adjacent sockets,V1 into V2,V2 into V1.
          One is the non vibrato channel,the other is the vibrato channel.The tube types are stamped into the metal in the front of the AO29 amp.
          6AU6 have a metal shield covers,the only 'pair' with covers(12AX7 isn't a pair)......
          We need to verify the tubes operate correctly,and at this point you have only one working correctly.
          If the vibrato channel starts working and the non vibrato doesn't after the tube swap, we have narrowed it down to at least a bad 6AU6 tube.
          Many times it is only a tube or dirty/shorted contact on a pin or socket that causes this issue.Seldom is it the tube,they lose volume usually before they totally give it up.
          I swapped the 6AU6s with no good result. Same issue remains.
          What's next?
          I have a V-Ohm meter, and a working knowledge of simple amplifiers.

          Comment


            #6
            Have you cleaned the tube socket of the vibrato channel and pins of the tubes? Seldom do they just 'quit'.
            I gently tap tubes with a pencil eraser(same eraser I clean tube pins with).
            This sometimes wakes up the element of the tube not working,notably the 6V heaters seem to come and go with any corrosion or dirty contacts.
            Sometimes it's just a bad connection.Before opening it right up try a different 6AU6 and clean that socket and those tube pins.
            Compare voltages of the adjacent 6AU6 socket pins and see if they match with your multimeter?
            They won't be exact matches but should be close give or take 20%?

            Every person with an old Hammond should have spare tubes,not often needed,sometimes though they do wear out.
            It could be an open resistor,that amp is a half century old at least.....
            sigpic A100/251 A100/147 A102/222 B2/147 BCV/122 M3/145 M102/145
            Various modern keyboards and modules.

            Comment


              #7
              Generally if the tube swap doesn't fix it, it is highly probable that the screen grid resister on V1 opened. One additional tube to check is V3 which is used to drive the signal to the vibrato line box. Try swapping V3 with V9 (the 12AU7 used in the perc circuit.
              If that doesn't fix it, remove V1 & V2, Carefully compare the DC voltage on pins 5 (plate) and 6 (screen grid).

              Jim

              Comment

              Working...
              X