Preamp Valve Issue?

Discussion in 'Amps [BG]' started by GrumpiusMaximus, Mar 27, 2014.


  1. GrumpiusMaximus

    GrumpiusMaximus I've Seen Things You People Wouldn't Believe Supporting Member

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    Hello all.

    I have searched but please point me in the right direction if this has been discussed many, many times before.

    For the last few weeks, my amplifier (more about that later) has been having issues with the clean channel. I plug my basses straight in and the volume is low - audible but low. Occasionally it will spark into life but then it will go back to its reduced state. The distortion channel works absolutely fine.

    After doing some reading, I came to the conclusion that the issue is a preamp valve. This is reasonable because as far as I know the valves haven't been changed since the amp was new (and I bought it second hand about five years ago). I've now purchased some new ECC83 (12AX7) valves from the helpful folks at Watford Valves and I'm awaiting delivery.

    I just wanted to check a few things with you guys:

    Firstly, is my diagnosis reasonable? Does it sound like a preamp valve issue?

    Secondly (here's the part where I expect some flak) the amplifier in question is actually a 1x12 guitar amplifier (Laney LC-30II). I'm quite happy with its performance - especially the distortion channel - with my basses but is there any possibility that the preamp section could be affected by regularly playing bass through an amp that is primarily intended for electric guitar?

    My first thoughts are 'no' and the fact that it's a 1x12 suggests that it should be able to deal with bass frequencies just fine but I thought I'd check with the vast knowledge base here. Apologies for my ignorance!
     
  2. BurningSkies

    BurningSkies Supporting Member

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    It could be a tube problem and 12AX7's are cheap enough that it certainly would be an initial go-to for most people. It could also be a dirty connection (input, loop, etc) that's causing it or a host of other things. You'll known when you try those new tubes. :)
     
  3. GrumpiusMaximus

    GrumpiusMaximus I've Seen Things You People Wouldn't Believe Supporting Member

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    I hope it's just a preamp valve issue.

    On the other hand, the Ampeg PF-350 is currently on my GAS list. It might be just the excuse I need...

    If I end up having to replace the EL84s and rebias it, I'll be even more tempted...
     
  4. InsanityAmps

    InsanityAmps Supporting Member

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    Could be a preamp tube or effects loop like BurningSkies says. An easy check to see if it is the effects loop is to plug a cable from the send into the return and try the amp out. If if works fine after that, you know it is your problem. I kind of doubt that is the issue though since it only does it on the clean channel. To me that points to a preamp tube, socket, or something making a bad connection inside. Running a bass through the amp will not cause a problem like you are describing.
     
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  6. Downunderwonder

    Downunderwonder

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    Guitar 12's aren't meant for bass frequencies. Be wary of the distortion channel. You probably won't hear the speaker farting.
     
  7. BassmanPaul

    BassmanPaul Gold Supporting Member

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    It doesn't sound like a valve, that was really odd writing valve instead of tube, problem as it "sparks to life" and performs properly. It could be a poor contact at the valve base or elsewhere. If you can physically reach the tube, "wiggle", technical term there, the tube around to see if that helps. :)
     
  8. GrumpiusMaximus

    GrumpiusMaximus I've Seen Things You People Wouldn't Believe Supporting Member

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    I'll give that a go tomorrow, thanks mate. I'm quite happy to disassemble the whole thing if necessary but I don't think it will be necessary. Even if that's the problem, it's getting a new set because it's definitely due a new set.

    Typing valve instead of tube? Suck it up!

    I'll look into the effects loop diagnostic, too. That's a great help.

    As for the speaker being a problem? It hasn't been a problem since I've been using it that way but I'll be wary. I haven't played it at any substantial volume since I've owned it (bedroom warrior, as it stands) but if I blow the cone, I know where I can get a better replacement anyhow.
     
  9. GrumpiusMaximus

    GrumpiusMaximus I've Seen Things You People Wouldn't Believe Supporting Member

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    Update.

    All sorted. It was a preamp valve in the end. Went with some Tung-Sols.

    Thanks for your collective advice.
     

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