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Advice needed please...

Hi, I just picked up a vintage Yamaha YBA 65 bass amp... It needs some attention.

The symptoms are:

  1. 'motorboating'
  2. giving a friendly shock when you touch it or the cable jack on the guitar

Can I take it to local electronic repair shop (quick solution, cheap transport){maybe it's just a ground issue} or should I take it to an amp repair shop in Durban (longer, expensive transport)?

  • V8 replied to this.

    Tom333 Heya - nice find! The old solid state Yamaha amps have a warmth a lot of the newer SS stuff just doesn't have. Worth a fix!

    If your local repair guy has an idea of how to fix audio stuff, that makes life easier. I know little about electronics, but sounds like there's a ground/earth issue somewhere?

    Were you in Cpt I could reccomend a few guys, but in KZN/Dbn I dunno.

        Thanks. Local would be better, the thing weighs a ton:

        I am too curious so I snooped around, the earth wire in the plug had been pulled out, (shocking issue solved-duh).
        And interestingly the wire coming from the volume pot seems to be the source of the 'motor boating' (I think.) When I touch it or even put my finger near it (1-2mm) the 'motorboating' gets more intense.


        • V8 and RCVN like this.
        • V8 replied to this.

          Tom333 Easy fix on the plug - nice!

          Also looks super clean in there - hopefully the tech won't savage it. Just in case ...careful poking around, caps hold charge if not discharged properly...it's a lesson I've not had to learn 😁

              5 days later

              That thing looks awesome.

              Let us know if it you can get it sorted.

                5 days later

                I have been looking around the net for info. And came across a few things.

                I cleaned the pots out with contact cleaner, this got rid of the scratchy noise when adjusting knobs, mainly the volume. (still a buzz coming from the volume wire)

                When I put it back together, there was a new sound, like a giant fly buzzing around. symptoms pointed towards grounding issues again, so I removed the two ground wires and cleaned them with glass paper. There was some rust/muck build up. And changed the old plug for a new one. Buzzing went away.

                Then found a crack on the speaker where cone meets "ruffled skirt" (thats a term, right?) , so followed advice and cynoacrelated it but no change in distortion. Then tested the speaker with a multimeter, 8ohms at the amp outlet, and 70ohms at the speaker! I fear the speaker is toast.
                ...is it fixable, do I need to replace it or rebuild/re-cone it?
                I'll phone the local music shop and ask if I can bring it in to be tested, if they do such a thing. I think this is going to be a long project amp.

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