Ad Widget

Collapse

Announcement

Collapse
No announcement yet.

Ampeg BA-115T keeps blowing fuses!

Collapse
X
Collapse
 
  • Page of 1
  • Filter
  • Time
  • Show
Clear All
new posts
Previous template Next
  • #1

    Ampeg BA-115T keeps blowing fuses!

    Hi forum I hope you can help me out with this amp,

    I have an Ampeg BA-115T which keeps blowing fuses, after it failed the first time I read several threads to learn common problems with this amp.

    So far I've replaced output transistors and the main bridge rectifier since they were fried, after I replaced these, the fuse blew but the components were not destroyed. PS caps are not shorted.

    Then I tested the transformer and it works fine. Disconnecting the tranny secondaries from the board won't blow the fuse. This tranny features two secondaries, one center tapped for the preamp, power amp and voltage multiplier circuit (since the amp has a tube) and the other secondary feeds the tube's heater DC supply.

    If I connect just the heater secondary the amp doesn't blow the fuse... The amp features two zener voltage regulators to feed the preamp and bias circuitry, so I disconnected R66 and R68 (please refer to the attached schematic) from the board to further isolate the problem but the fuse blew again, so it seems to be something in the power amp section or voltage multiplier circuit.

    Any ideas?
    Attached Files
    Tags: None
  • #2
    1. Use a light bulb limiter to stop blowing fuses. Then you can do some useful debug.
    2. It is very likely to be the odd voltage multiplier circuit. Remove R74, see if the voltages come back up and the fuse blowing stops. If so, it's in the multiplier or the power amp.
    3. If the preceeding test says multiplier or power amp, pull the output tubes, test each part in the multiplier and fire it up without tubes. If the B+ is present, you probably have fixed it.
    4. Those zeners supplying the preamp are a disaster waiting to happen. This is unrelated to your current problems, but it's still there as a design defect.
    Amazing!! Who would ever have guessed that someone who villified the evil rich people would begin happily accepting their millions in speaking fees!

    Oh, wait! That sounds familiar, somehow.

    Comment

    • #3
      Um...

      Only tube in it is the one 12AX7 in the preamp. No power tubes.

      Running the powr amp without the +/-16v is not a good idea

      If replacing the outputs is not enough, then check those pairs of back to back zeners at each output and also check the two MJE driver transistors.
      Education is what you're left with after you have forgotten what you have learned.

      Comment

      • #4
        Originally posted by Enzo View Post
        Um...
        Only tube in it is the one 12AX7 in the preamp. No power tubes.

        Running the powr amp without the +/-16v is not a good idea
        Doh! I have inserted my foot in my mouth, apparently because my brain cavity was at least momentarily empty! S'wat I get for doing a drive-by glance at the schematic.

        You are correct Enzo.
        Amazing!! Who would ever have guessed that someone who villified the evil rich people would begin happily accepting their millions in speaking fees!

        Oh, wait! That sounds familiar, somehow.

        Comment

        • #5
          R.G. Does that DOH! come with an Enzo whack on the forehead?

          Comment

          • #6
            Originally posted by 52 Bill View Post
            R.G. Does that DOH! come with an Enzo whack on the forehead?
            Yep. I've applied the self-whack already~! 8-)
            Amazing!! Who would ever have guessed that someone who villified the evil rich people would begin happily accepting their millions in speaking fees!

            Oh, wait! That sounds familiar, somehow.

            Comment

            • #7
              Thank you guys,

              Got the amp working, as I mentioned I replaced the bridge rectifier and outputs, apparently I had something not connected properly which caused the fuses to blew.

              I adjusted bias and then turned the amp on with the speaker connected having a CD player as input. Now I get loud and intermittent pops, crackles and sometimes loud static, I suspect something is disconnected/loose since this seems to get worse at high volume levels.

              Any ideas?

              Comment

              • #8
                A fairly common problem on these amps are cold or broken solder joints on the pc board. I've also seen the break jacks (FX loop, etc.) cause all sorts of problems as well.

                Clean all of the jack connections, and try tapping around the board with a chop stick and see if you can cause the problem to happen.

                Comment

                Previous template Next
                Working...
                X