18W problem

Discussion in 'Amp Tech Center' started by Orpingtons, May 27, 2019.

  1. Orpingtons

    Orpingtons Tele-Meister

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    Hello,
    I have this 18W clone that used to sound formidable. All of a sudden, the amp produces very low volumes and it sounds like it's wide open (full gain and volume cranked but with very low volume)... I wonder what could be wrong... Any suggestions or advice would be greatly appreciated.
     
  2. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    It would help to know your level of tech skills before we start and recommend too much. If you're not comfortable cracking it open and dealing with high voltages about the only thing you can do is swap tubes.
     
  3. Dacious

    Dacious Poster Extraordinaire

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    Your tubes are probably worn out. 18 Watters run them pretty hard.
     
  4. Orpingtons

    Orpingtons Tele-Meister

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    I feel comfortable cracking open the amp.
     
  5. Milspec

    Milspec Friend of Leo's

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    Sounds like tubes to me as well. Volume loss like that is a common trait of failing tubes.
     
  6. dogmeat

    dogmeat Tele-Afflicted

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    18 whut?
     
  7. jtcnj

    jtcnj Tele-Holic

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    like was said.
    Power tubes wear out.
    el84 cathode biased amps - what your circuit probably is - runs those tubes hard.
    But check to see what is there.

    Tube Depot I have bought from numerous times will match pairs free and burn in for $2.00.
    Prices are good and shipping is reasonable and quick.

    The russian (EDIT to correct model) 6P14P-EV is a good , robust equivalent that is available on ebay. Get -EV variant; they are supposedly better matched to the higher plate voltages in these circuits.
     
  8. Wayne Alexander

    Wayne Alexander Friend of Leo's Silver Supporter

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    First step is to remove the tubes and spray some NON-LUBE contact cleaner into the tube sockets, and then push the tubes in and out a couple of times to clean the contacts. If that doesn't help, swap tubes. If that doesn't work, crack it open and look for loose solder connections/burned components. Beyond that, http://www.geofex.com/ampdbug/ampdebug.htm
     
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  9. charlie chitlin

    charlie chitlin Doctor of Teleocity Silver Supporter

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    Why non lube?
     
  10. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    You don't want the tube pins to be slippery.
     
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  11. Wayne Alexander

    Wayne Alexander Friend of Leo's Silver Supporter

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    If you put lube type contact cleaner in a tube socket you can cause a fire. You want the type that removes corrosion & deposits, not the kind that leaves a deposit. The lube type is for lubricating rotating parts like pots, which don't get hot.
     
  12. philosofriend

    philosofriend Tele-Holic

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    If new tubes don't fix it, and you understand the basic concepts of electronics and know the safety rules.......

    Jack Darr's book, "Electric Guitar Amplifier Handbook" is a great book. It was written in 1965 to help TV repairmen not be afraid to fix guitar amps. He deals thoroughly with tracking down the stuff that most often goes wrong. There is a new reprint, because the book just keeps on selling. The newer books that I have seen are daydreamy and modification oriented. Darr's book is just about "here is what you need to know to find the problems quickly".

    There is no short cut around understanding the job that the resistors and capacitors around the tubes are doing. In other words, it takes some study to become an amp repairman. Darr's book plus the RCA tube manual have the stuff that needs to be studied.

    As I recall, the likely culprits of loss of volume plus distortion are: Power supply problem, shorted or open capacitors (coupling or bypass caps), resistors open or changed values (plate load resistors, resistors involved in bias).
     
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