HELP! Weird distortion.....Sometimes...???

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by cap'n'crunch, Feb 19, 2009.

  1. cap'n'crunch

    cap'n'crunch Member

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    Laney AOR ProTube 50. Sometimes when I play it I get a nice Marshally crunch that is very similar to my 2204. Other times it sounds like crap. I'm not talking about a little crap. I'm talking about a big fresh pile of crap. It's like super saturated lows even with the gain low and theres a square wave clipping/buzzing when I first strike a chord. So, I shut her down a try it again a couple days later and it sounds fine.. Has nothing to do with wether its warmed up as it will do it randomly even when first switching it on.
    I borrowed the tubes from my 2204 and biased them in and it still does it randomly. Any ideas? EDIT: I used all known good tubes from some other amps I have.

    Thanks
     
    Last edited: Feb 19, 2009
  2. SatelliteAmps

    SatelliteAmps Member

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    If it happens randomly, then it is something intermittant inside the amp. How good are you at using a multimeter?
     
  3. Ronsonic

    Ronsonic Member

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    Start with the FX loop. Just plug a straight cable from the send to return and see if that fixes.

    Also be sure all the preamp tubes are clean and well seated in the socket.
     
  4. Structo

    Structo Member

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    First suspects are always the tubes.

    Second suspects are the tube sockets. Clean and re-tension (be careful).
    You must have the filter caps discharged to do this.
    I like Caigs contact cleaner the best for this.
    Spray some on a tubes pins, then plug it in and out of the socket.

    Another trick if you know how to safely work on the inside of the amp is to use a pipe cleaner and spray some cleaner on it and run it through the socket pins.

    If you don't know how to safely work on an amp take it to a tech because there are 300-500 volts inside that will stop your heart from beating if you touch the wrong thing.

    As mentioned sometimes the switching jack(s) on the FX loop can become corroded or dirty. Sometimes you can help it by plugging in and out several times.
    If that improves it you may need to take the amp apart and clean the switch on the jack manually, but if it is an enclosed jack, you will probably need to replace it (them).
     
  5. cap'n'crunch

    cap'n'crunch Member

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    Thanks.
    Yeah, I've experience discharging filter caps by running a wire with alligator clips from #1 pin on V1 to ground on my 2204 and replaced its filter caps myself and cleaned the sockets. I check with a multi meter to makes damn sure they are discharged.

    So, anyway, Whats the best way to re-tension the sockets? May not be my problem but, I'd like to do it anyway for routine maintainance to all my older amps.

    Thanks again for your reply.
     
  6. cap'n'crunch

    cap'n'crunch Member

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    Fairly good I guess.
     
  7. rockon1

    rockon1 Member

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    Good advice already posted. Simple stuff first! Re cap-Clean and retension tube sockets. Clean pots. Put cable in FX loop jack. If it helps clean the contacts.

    Ive used a dental pick to retension the sockets on mine. Be careful not to distort them Bob
     
  8. Ronsonic

    Ronsonic Member

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    Retensioning sockets is NOT routine maintenance. I get as many amps with sockets damaged by someone trying to retension them as I do sockets that need retensioned. Seriously, this is what you do to avoid replacing a socket. Cleaning sockets is routine maintenance. Actually, bending tube pins is probably better and safer for most people than mucking around inside the socket at least for 9-pins.

    Anyway, back to this amp. The problem is random and intermittent, which means most likely mechanical, a connection. If it were tubes, the tube swaps would've told us something.

    "Simple stuff first" is a damn good place to start.

    FX Loop. Dirty normaling contacts can cause distortion and loss of signal, it takes a cable and 10 seconds to check.

    Input jack and controls, with the amp on plug in and give it some signal and work the pots and the plug. Any change, jumps, bad noise. A crudded up control can do bad things. While we're doing this take a moment put it on standby and exercise every jack and control on it. Run a plug in and out of every jack about ten times. Run each control back and forth and flip every switch. Very useful preventative maintenance. Same thing applies to tubes, with the amp cold run each in and out of the socket 3-4 times.

    Now from the back with the amp running and some tone or sound, jack a low level music signal into the amp if you don't have anything else. Put a finger on the top of each preamp tube and push it around a little. Drop out? Noise? Clean sockets. Same for the power tubes, but they'll be a bit hot to handle. You can grab them with a piece of cloth, or better 3M scothbrite, or just shove them around a little with a rubber covered screwdriver handle or some such. With the amp running tap on tubes near the top with that same rubber covered implement. You don't want to break anything, but if something is loose you'll want to provoke it. The shoulder where the tube necks down near the top is the strongest point. Some noise is normal, not much, and no crackling or arcing.

    Percussive diagnostics. Does the amp respond to being beat upon? Dropped from a few inches? shaken? Don't be bashful. The amp can take worse going to a gig. Does this affect the problem?

    Start there, then we'll get around to opening it up.
     
  9. cap'n'crunch

    cap'n'crunch Member

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    UPDATE: Well, I came across a cap on the board that looked physically out of place compared to the other ones. Come to find out that someone put a .001 where a 22n should be. I replaced it with the correct cap and it sounds much better now but, still a bit grainier than my 2204 but, I here others compalin of this too so, maybe normal??? The amp is brighter now too. I wonder if this was someones bright idea of a warming mod gone wrong.

    Thanks
     

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