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AMPEG V5 issues and schematic handout

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  • #1

    AMPEG V5 issues and schematic handout

    i was able to track down the schem for this beast. and i'll send a copy to whoever needs it, it's a PDF just PM me if you'd like a copy, it's kind of rare.

    i've also posted a JPG of the schem here:
    http://s43.photobucket.com/albums/e3...pegv5schem.jpg

    ok...i tracked this schem down because a friend of mine broke his V5. he says it was absolutely fine one day and the next time he went to turn it on, the power light came on but nothing else. no standby light, no tube filaments, nothing.
    the power light is a light up switch similar to a marshall rocker switch but narrower. the AC goes from the wall directly through a soldered internal fuse to the externally-accessible mains fuse to the power switch before if hits the PT.
    i checked every wire coming out of the PT for voltage and couldn't find any.

    is this an obvious case of a dead PT? i thought they went gradually? this seems to be an all-of-the-sudden thing.
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  • #2
    No, not obvious at all. You said you found no voltage on any wire from the transformer. Well at least two of those wires are the primary, should be mains voltage on them.

    Find the primary leads and verify 120VAC or 240VAC or whatever your local mains are on the primary leads. If it gets there, there may be an open primary. In that case, disconnect the primary wires and measure resistance between them. I have no idea how many ohms it will be - 10, 40, 100, 200? - but it shouldn't be open. On the other hand, if the mains voltage doesn't get to the primary winding, then find out why. DOn't eyeball teh fuses, measure them with a meter. Pull them from the fuse holder for this. Soldered in fuse? FIne, pull the other fuse. They are in series, so pulling the other removes the wired in one from the circuits. Measure the on resistance of the power switch, make sure it works. Fuse OK? FIne, measure it in the holder to see if the holder is working too. Check continuity through the entire primary circuit. All we know now is that mains voltage gets as far as the power switch. The switch can still be broken.
    Education is what you're left with after you have forgotten what you have learned.

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    • #3
      i thought they went gradually? this seems to be an all-of-the-sudden thing.
      Why would you think that? Transformers are pieces of wire wrapped around a core. The wire is open or it is not. The wire is either shorted to another wire, or itself, or the frame, or it is not. SOme failures such as shorted adjacent turns might not load one down so much as to make it blow fuses, but it will run hot and possibly reduce voltage. but mostly I do expect transformer to fail suddenly.
      Education is what you're left with after you have forgotten what you have learned.

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      • #4
        I had one of those MTI Ampegs in the shop about 7-8 months ago. Exact same problem, open primary winding on the power transformer. I remember it, cause it was the only one I'd ever seen. Basic 100w Marshall copy.

        Maybe a common problem? I assumed that there was an internal thermal fuse that opened up. Customer balked at replacement or repair cost, so I never tried to open it up to find out for sure.

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        • #5
          Originally posted by 52 Bill View Post
          I had one of those MTI Ampegs in the shop about 7-8 months ago. Exact same problem, open primary winding on the power transformer. I remember it, cause it was the only one I'd ever seen. Basic 100w Marshall copy.

          Maybe a common problem? I assumed that there was an internal thermal fuse that opened up. Customer balked at replacement or repair cost, so I never tried to open it up to find out for sure.
          Me too and I got the exact same response from my customer!! Except this was a local repair, you'd think it was the same guy. ha ha.
          Bruce

          Mission Amps
          Denver, CO. 80022
          www.missionamps.com
          303-955-2412

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          • #6
            AC gets to the primary. fuses and fuse holder are all good.
            i clipped one primary wire off of the power switch and measured resistance between it and the other wire still on the switch. it reads around 900k.

            there are three other wires coming from the PT through the same chasis hole, one is green/ground and the other two are white and brown(respectively) and are taped off and not attached to anything. the two wires going to the switch are red and orange (respectively).

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            • #7
              If the primary winding reads 900k, then it is open. As in bad transformer.
              Education is what you're left with after you have forgotten what you have learned.

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              • #8
                what info would i need to source a new PT for this amp?
                any good suggestions for me where i might find a decent replacement as an original is probably not an option for such a rare amp?
                thanks.

                Comment

                • #9
                  As any amp, add up the heater currents and spec for that. Then figure out the AC needed for the B+ target voltage. And figure current based upon output power. Puts you in the ball park.

                  Or just look for PTs from amps of similar output power, tube set, and voltage.
                  Education is what you're left with after you have forgotten what you have learned.

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                  • #10
                    thanks again, enzo!
                    i'll update the thread if/when events move forward!

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