Amp trouble: Half volume?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by JoshuaTSP, Jan 11, 2008.


  1. JoshuaTSP

    JoshuaTSP Senior Member

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    Well, I own a Rocktron Vendetta combo and I've had it for a few years. Problem is: I fired it up yesterday, and it barely had any volume. :eek: So my first thought is that a tube is dead. So I swap out each preamp tube........in certain combinations I had absolutely no sound. :eek: So I kept swapping....found a combination with the bad tube supposedly out. Now the amp only plays half volume, not half power. It's simply just not as loud as it was earlier this week. What could it be?

    Here's the cronological order to what happened:

    Last week: Swapped out EL34s for 6CA7s......(biased with test points). Also changed out most of the preamp tubes.....added Tung sols.
    This week: Played it all week fine and actually was sounding REALLY good. Shut it down two days ago in working order.
    Yesterday: Turned it on to jam......noticed the volume difference right away. Swapped preamp tubes. Since that didn't work, I put the old EL34s in it and re-biased. Still half volume. It sounds fine, just quiet.....the global density and presence don't seem to do as much either. I can crank the master volume to get it loud, but normally anything past half way would blow my windows out.

    Can anyone help?
    I'm trying out for a band next wednesday.:puh
     
  2. Blue Strat

    Blue Strat Member

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    Are you plugging directly into the amp? If not, try that.

    Can you put EVERYTHING back to where you were before you started doing tube swaps?

    Got your speakers plugged into the right jack?
     
  3. JoshuaTSP

    JoshuaTSP Senior Member

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    Yes. I thought maybe one of my effects had gone bad...I even tried different guitar cables....just to be sure.

    yep. I triple checked everything....along with trying a different cab.

    Right now I'm at work....so I can't put it all back the way it was at the moment...but I could later? I can tell you exactly how I had it.

    All I can find for help is this: http://www.geofex.com/ampdbug/lowpower.htm
     
  4. JoshuaTSP

    JoshuaTSP Senior Member

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    Could it be dirty sockets?
     
  5. rooster

    rooster Member

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    Check for dirty jacks as well. Oh, and check if your guitar is turned up.:D

    rooster.
     
  6. JoshuaTSP

    JoshuaTSP Senior Member

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    :p

    I check the guitar volume knob.
    See I'm getting some volume just WAY less.

    I'm planning on buying some contact cleaner and spraying the tube sockets and FX loops jacks.
     
  7. JoshuaTSP

    JoshuaTSP Senior Member

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    Come to think of it......I used the FX loop for the first time a few days ago? It worked after I unplugged though?

    I read that I can plug directly into the effects loop to see if it's a preamp or power tube problem?
    If I plug into FX loop, and the volume is unchanged, then there's something up with the power tubes......if I plug into the FX loop and it's louder, that means I have a preamp problem?
     
  8. JoshuaTSP

    JoshuaTSP Senior Member

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  9. rockon1

    rockon1 Member

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    Good idea. Dirty contacts in FX loop jacks can lose signal or dirty tube sockets. If that doesnt do it you might have gotten a bad pair of power tubes or something so as Mike said swap the old ones back in. Go direct from guitar to amp too so to eliminate any posible bad cables. Bob
     
  10. JoshuaTSP

    JoshuaTSP Senior Member

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    I'm going to give the cleaning a shot before I spend any money on repair.

    So I can just spray the tube, and push it in and out to clean it?
    And the FX loop I can just spray right in the 1/4 jack?

    I have been changing preamp tubes quite a bit lately....the sockets may be loose? I don't know if I'm brave enough to drain caps yet........
     
  11. slider313

    slider313 Silver Supporting Member

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    Be sure to use a contact cleaner with no lubricant. I use CRC Quick Dry which sells in Home depot for about $6.00 a can. When cleaning the sockets, just spay it in the socket itself and work a tube in and out five or six times. With the input jack, spray the end of the jack tip and do the same.
     
  12. JoshuaTSP

    JoshuaTSP Senior Member

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  13. Dave Orban

    Dave Orban Gold Supporting Member

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    I had that happen to my Matchless Chieftain a year or so ago. Turned out to be the output tranny.
     
  14. Mayor McCheese

    Mayor McCheese Member

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    That's what I was thinking.
     
  15. JoshuaTSP

    JoshuaTSP Senior Member

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    Well, that would be swell. :mad:
     
  16. JoshuaTSP

    JoshuaTSP Senior Member

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    Are there any other symptoms of a blown OT?
     
  17. Blue Strat

    Blue Strat Member

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    For the hell of it, run a short cable between the effects send and receive. Maybe you stirred up something with those jacks when you tried the effects loop the other day.
     
  18. Blue Strat

    Blue Strat Member

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    Forget about the OT. There are 400 more likely things to be wrong.
     
  19. JoshuaTSP

    JoshuaTSP Senior Member

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    Figured it out!

    Turns out it was TWO bad preamp tubes.

    I ended up contact cleaning everything just to be sure.

    One brand new Tung Sol...was causing the volume drop. I put the 6CA7 power tubes back in and no go. So I started with the P.I., still low volume. Moved on to the V1, and that was it.

    I was also experiencing a ticking...kind of like a metronome....turns out that was a bad preamp tube. I don't know.

    Thanks for all of the help!!!!:AOK
     
  20. rockon1

    rockon1 Member

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    Good to hear it was a simple fix! Curious where did you purchase the pre amp tubes from? Bob
     

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