Jammed Ohm Selector . . . Help please

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by bpalatt, Apr 21, 2005.


  1. bpalatt

    bpalatt Guest

    I have a laney from the mid 80's that just recently blew the low power fuse. This never happened before. I discovered, afterward, that my ohm selector is jammed in between 4 and 8 ohms and assume this either caused or resulted from the fuse blowing. I have replaced the fuse, and when I jiggle the ohm selector I get sound intermittantly, otherwise I get nothing. It is the dial type selector with slot in the middle for turning to choose beween 4, 8, and 16 ohms. Can I fix this problem? If so how? Any help would be much appreciated. Thank you.
     
  2. John Phillips

    John Phillips Member

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    You almost certainly must replace the switch. It's probably the cause, not the result.

    Don't try to operate the amp with it faulty, at the very least you'll put severe stress on the tubes if it's shorted, or risk blowing the OT if it's going open-circuit. This would definitely explain the blown fuse too.
     
  3. bpalatt

    bpalatt Guest

    Is it possible to fix the broken one, or do I need to get a new one? I didn't mention in my previous post that I have tried numerous times to move it in any direction, and it will not budge. Thanks again.
     
  4. John Phillips

    John Phillips Member

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    You're going to have to change it I think. It sounds like the mechanical detent mechanism has broken, jamming the switch. Hard to say exactly what's broken, but it's likely to be a plastic part of some sort. Older plastics like this do tend to go brittle with age and heat. Given the fairly critical nature of the part, it's probably not a good idea to try to fix it unless you can be certain it will be reliable afterwards.

    I'm not certain (it's a while since I saw one) but I think the selector is similar or identical to the ones on 80s Marshalls, so it shouldn't be too hard to find a replacement.
     
  5. rooster

    rooster Member

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    Those '80's Marshall selector switches are at www.tubesandmore.com. I think they're about $20 or so.

    rooster.
     
  6. bpalatt

    bpalatt Guest

    Thanks guys. I figured I would have to replace it. I just wanted to make sure this wasn't a known problem with a quick fix that I was unaware of. Is there something else that might have failed to cause it to melt or jam? Perhaps a bad power tube or output transformer?
     
  7. rooster

    rooster Member

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    They're not really the most ruggedly built units. I use a tube socket on my amps, with 2 extra keyways filed out, and a tube socket with a solid #14 wire soldered between two of the pins, and filled with silicone, and then capped off. It functions a lot like the old JMP selector, but with an easily replaceable part.

    rooster.
     
  8. doctord02

    doctord02 Member

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    Ha, thats a nice trick Rooster - I'll have to try that on my homebrew builds... I hate wiring up/buying the overpriced selector switches.
     

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