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Fried WT-400?

Discussion in 'Amps and Cabs [BG]' started by lump, Jan 10, 2004.


  1. lump

    lump

    Jan 17, 2000
    St. Neots, UK
    Crap.

    Working mids, and went to church this morning after about two hours sleep. Set up my amp, tried to play--no sound. Looked down and saw that in my sleep-deprived state, instead of plugging the cab end of my speaker cable into the cab, I had plugged it into the "send" port on the amp (I have no clue how I managed that). Oops. Removed it and plugged it into the cab. No sound. No smoke or burning smell, just no sound. Checked the fuse; looks fine. Opened up the amp, everything looks fine (not that I could tell if it weren't).

    So, here's my question. I don't know whether plugging the cable in like I did had a causative affect, or whether it is just coincidental and there is some other problem. Is doing what I did enough to fry it? And if that probably IS the problem, what sort of damage did I do, and what would I be looking at to get it fixed?

    Help...
     
  2. notanaggie

    notanaggie Guest

    Sep 30, 2003
    If I have understood you correctly, you had a cable that was plugged into the power amp out, and you mistakenly plugged the free end of it into the "send".

    (BTW, I have been dead-tired too, and I refuse to discuss what an idiot I have been in that condition)

    Presumably that is the "send" of a "send/return" loop, which usually is in series with the pre-out going to the power amp.

    There are a number of possible bad things that may have happened, or it could be co-incidental, I guess....

    Depending on how the "send" is set up, you could have fed the output back into the input, which may have caused a damaging oscillation. Probably that would have blown the fuse if anything bad had occurred.

    Second, you may have simply fried the "send" circuit. Since that is usually in series with the signal to the power amp, messing it up can cause a "no sound".

    Knowing no more than you said about the unit, I am guessing that #2 is the "winner" here.

    That can happen without any visible damage. The innards of the amp at that point may only be able to handle 15 volts, and you might have fed them 30 or 40 thru the jack when you tried to play thru the amp while it had the cable plugged like that.
     
  3. lump

    lump

    Jan 17, 2000
    St. Neots, UK
    Further analysis reveals:

    Amp will play bypassing the preamp through the aux ports. Bad tube? It's an Electro-harmonix 12AX7EH, and it gets plenty warm and looks fine. Fried preamp? Please let it just be the tube...
     
  4. lump

    lump

    Jan 17, 2000
    St. Neots, UK
    Thanks for taking the time to reply. Swapped fuses just in case; no joy. I also ordered another tube just in case that's the problem, since it's the cheapest thing to check first. But if the tube crapped out, does that mean the preamp will stop functioning altogether? Man, I hate d!cking with gear...:spit:
     
  5. notanaggie

    notanaggie Guest

    Sep 30, 2003
    A few volts won't usually kill a tube, they normally run using a couple hundred. But something else might have bitten it.

    If it works without using the preamp, that pretty well puts the finger on it as the pre got damaged.

    If there are any "protective" parts like diodes etc, they might have sacrificed their little silicon lives trying to protect the rest of the unit.
    If so, with a little schematic info you could be up and running by snipping their leads (and replacing them at leisure).

    I am NOT recommending any snipping unless you know what you are cutting, and why. Its tech time!
    Your profile suggest that you may have access to bored technicians at the base electronics shop.......'nuff said.
     
  6. lump

    lump

    Jan 17, 2000
    St. Neots, UK
    Yeah, other than pulling the tube, I ain't remotely qualified to go digging around in there. It's just barely under warranty (if they don't read this thread ;) ), but shipping would cost an arm and a leg and could take up to 45 days each way. I emailed Eden to see if they have an authorized service center in Korea, but so far no response.

    Anyone else got any ideas?
     
  7. jive1

    jive1 Moderator Staff Member Supporting Member Commercial User

    Jan 16, 2003
    Alexandria,VA
    Owner/Retailer: Jive Sound
  8. lump

    lump

    Jan 17, 2000
    St. Neots, UK
    Thanks. I did read that thread before I posted here, but a re-read brought me a step closer to figgering things out (maybe). Like I said, the aux in (post-EQ) works, but I hadn't tried the return in. The return in is pre-EQ, but post-tube/compressor/enhance. Lo and behold, using the return in, the EQ works. The compressor/"suck knob" do not, as expected. So I'm HOPING it's just the tube (if my math on this is wrong, someone correct me). Unfortunately, the only guy I know who might have a spare tube (a geetar player) is TDY right now, so I gotta wait on the mail. :meh:
     
  9. lump

    lump

    Jan 17, 2000
    St. Neots, UK
    Hey, check this out. Got a reply from the man himself:

    -------------------------------------
    Hi,

    I think you fed the power amp back through the effect send. In general amps are not set up for that particular circumstance. You probably fried IC #U2 . Get a tech to replace that chip (TL072) and you should be OK. Good luck.

    David Nordschow

    -------------------------------------

    Apparently, USM isn't the bogeyman some folks here thought it would be. ;) They also gave me a contact # for a tech here in Korea. I don't think I could ask for more, considering I'm the dumb@$$ who fried it (I gotta get a day job). I'll let you guys know how it all turns out. Thanks again, David!
     
  10. lump

    lump

    Jan 17, 2000
    St. Neots, UK
    Well, it ain't the tube. The good news is now I have a spare. ;) I also found out that www.electron-valve.com has pretty decent customer service. They were the cheapest I could find, and got the tube to me in about 10 days. I had to edjumacate them on shipping to an APO address, but it's all good. :)

    Korea is locked down for Lunar New Year (right now driving to Seoul, 30 miles away, is a 12-hour round trip), but next week I'll take it in. The guy up in Seoul sez he can have it back to me in a week. In the meantime, I'm using a buddy's SWR 4004, which does the job, but sounds a LOT different. It's not all bad, but I'm really not a fan of SWR. Man, this sucks. :spit:
     
  11. lump

    lump

    Jan 17, 2000
    St. Neots, UK
    Finally got my amp up to C2 Sound Reinforcement up in Seoul. Finding anything in Korea is always an adventure--there are no addresses or street names, so you kinda gotta know where you're going before you get there. Fortunately, I can get around in Korean pretty well, and Mr. Kwak, the C2 prez, can speak English fairly well (and somehow these things always end up with the Korean speaking English and me speaking Korean).

    Anyway, he gave me directions that at least got me near his shop, and said he'd pick me up if I called from there. I called him on my cell from a corner gas station, and I swear to God, by the time I put my phone away his van pulled up. There is no way I would have ever found his place--it was an unmarked warehouse back behind a bunch of other shops. He and his crew were super friendly, and after running the amp through a very nice Eden 4x10 (didn't notice which one), he concurred that is was the preamp. He's gonna order the parts(s) from David, then get back to me. The good news is that he has a contact down in my area, so he's gonna send the amp down to him when it's fixed. He also said that if it was just a minor repair he'd just charge me for the part and shipping. Groovy. :)

    In retrospect, the funniest thing about this is that no paperwork of any sort changed hands. I even offered to give him my credit card #, and he refused, saying I could just pay the dude down here. In the states, I would NEVER hand over a $900 amp without a receipt. Here, people just trust each other. Savages. ;)
     
  12. lump

    lump

    Jan 17, 2000
    St. Neots, UK
    FIXED!

    w00t, as they say.

    As promised, Mr. Kwak sent my beloved amp down to Heart One Sound, here in my neck of the woods. Finding the place was yet another adventure, and I know my way around here pretty well. Magellan couldn't have found it. Again, I had to be escorted in. Anyway, the amp is back in my hands and works like a champ. The best part? The repair cost me only $75, WAY cheaper than sending it back to the factory (which I suppose is the point of having overseas service centers). I cracked the case open just in case there were obvious blobs of solder, but it's immaculate. Mr. Kwak is the man. :cool:

    There is probably an object lesson in here about how military folks are pushed to the limits of endurance these days, but I'll spare you. Let's just say it's a good thing I was only setting up my amp, and not operating a weapon system. :meh:

    Anyway, kudos to David Nordschow, Mr. Kwak, and the entire Eden family. OUTSTANDING customer service. Thanks again to those who posted as well. TB rocks!
     
  13. Starrchild

    Starrchild

    Nov 10, 2000
    The Bay.
    Good for you.

    Now go rock :bassist: