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Peavey 400 Classic problem...

Discussion in 'Amps and Cabs [BG]' started by mlwarriner, Mar 14, 2006.


  1. mlwarriner

    mlwarriner Supporting Member

    Nov 8, 2003
    KC, MO, USA
    ok. i bought it used and the previous owner had cut the wires to the cooling fan. too close to the fan housing to be able to re-attach the original fan. plus, i've seen around here that the fatory fans were noisy, so i just replaced it. used a 3" fan from radio shack. didn't bother too much with matching exact specs to the factory fan.

    problem: now that the fan is new, the amp is having "serious volume swells" (according to a buddy that was using it last night). he said "i feared for my speakers a couple of times".

    question: would the fan be causing this, or are there other issues at hand? i can't exactly describe what's happening, as i was not the one playing through the amp when it happend. buddy says "no effects, passive basses" so i don't think that's the issue.


    please help???

    thanks,
    mlw



    (ps - takeout, if you read this, feel free to add your comments, or correct any mis-information i may have given)
     
  2. Quadzilla

    Quadzilla Supporting Member

    Well according to Peavey engineer Bobby Baldwin (see the Classic 400 mega thread), the fan is not needed, but marketing wanted it there. Disconnect it and be done with it.
     
  3. jz0h4d

    jz0h4d

    Apr 26, 2005
    The Fan has nothing to do with it.
    The fan is a good ideal to increase the life of the amp and tubes.
     
  4. mlwarriner

    mlwarriner Supporting Member

    Nov 8, 2003
    KC, MO, USA

    when i emailed the peavey service dept about it, they strongly suggested not running it without a fan...

    dunno...
     
  5. takeout

    takeout Supporting Member

    Dec 27, 2002
    Kansas City area
    Since I was the one playing this particular amp last night, I'll chime in. I ran it to an Ampeg Classic 4x10 and 1x15, impedace switch set to 4 ohms to match (2 8-ohm cabs in parallel). Bass was a Rick 4003. I'm pretty good about right hand picking dynamics, but every once in a while, there'd be a BIG volume spike. I had the volume on the Clean channel on 3, no ridiculous EQ boosts. When it would do this, it sounded like my cones wanted to escape.

    Other than that, the tone was absolutely smokin'. Even my drummer noticed.
     
  6. The problem is probably not the fan.
     
  7. Quadzilla

    Quadzilla Supporting Member

    Agreed. As for the fan, mine is still hooked up, but I was thinking of putting a switch on it (toggle) and mounting it in the back. Honestly, I agree w Bobby and don't think the fan does much (adds electronic noise). I also modded my head for more airflow (took the wood cover off behind the front grill). It's tough to push this amp hard as it has soooo much power. It feels like a Ferrari doing 60 on the beltway. It always seems to have more power than I can use, so it's never pushed. 400 all-tube watts is a LOT of power! Mine never gets overly hot.
     
  8. mlwarriner

    mlwarriner Supporting Member

    Nov 8, 2003
    KC, MO, USA
    if it (probably) isn't the fan, then any other suggestions on what it might be?

    previous use of this amp didn't show any problems like this. then i installed the fan, and now it's doing it.


    :confused:
     
  9. Is the fan you got from Rat Shack AC or DC?
     
  10. mlwarriner

    mlwarriner Supporting Member

    Nov 8, 2003
    KC, MO, USA

    115vAC. i assume hooking in a 12vDC fan would have released the magic smoke almost instantly :D:D


    i don't know if the current draw of the new fan matches the old one, but i do know voltage is the same...
     
  11. Sudden volume swells usually indicate some kind of impedance/voltage problem. I really don't think it's the fan. You may have a preamp tube or its cathode resistor going out. Heat WILL exacerbate this, and the closed chassis of the Classic 400 doesn't cool the circuitry well, fan or no.
     
  12. mlwarriner

    mlwarriner Supporting Member

    Nov 8, 2003
    KC, MO, USA
    dunno how much it helps, but i did pull the board out from behind the front grille...
     
  13. Quadzilla

    Quadzilla Supporting Member

    Disconnect the new fan and see if your prob still exists...
     
  14. mlwarriner

    mlwarriner Supporting Member

    Nov 8, 2003
    KC, MO, USA

    that's part 1 of the current plan. part 2 involves taking it to a tech to see if he can find the problem (if it still exists after clipping out the fan)
     
  15. BbbyBld

    BbbyBld

    Oct 13, 2005
    Meridian, MS
    First of all, I never told everybody to go out and remove their fans if you read my post. I just happen to know that the amp will work fine without it.

    The fan is not causing that problem. It is hooked up across the AC line. I think it's just a coincidence.

    Have you experience any of these symptoms yourself since you got the amp back?

    I think it's very likely you have a bad pot. If you have trouble duplicating the problem, try turning the knobs and see if you get any dropouts. It could be a preamp tube. Another possibility is a loose connection on the screen supply or one of the other connectors going from the power transformer to the power supply board. Your friend may have run the amp for a while without a load and damaged one of the flyback diodes. One of the power tubes could be arcing and it's about to go out for good.
     
  16. mlwarriner

    mlwarriner Supporting Member

    Nov 8, 2003
    KC, MO, USA
    the problem just happened last night, and i haven't gotten the amp back yet.

    i did have some of the power tubes out to replace the fan. possible that i didn't get them back in correctly? or far enough? i'm sure that they all went back into the same sockets that they came out of...
     
  17. takeout

    takeout Supporting Member

    Dec 27, 2002
    Kansas City area
    Good - a Peavey guy in the house. I'll answer in turn:
    No bad pots that I noticed.

    All tubes were glowing evenly. Dunno how much of an indicator that is or isn't.

    Nope - I know better than to connect a tube amp sans speaker load.
     
  18. nt40lanman

    nt40lanman

    Jul 25, 2005
    Bobby, on running a tube amp without a load, is it bad without any signal going through as well? How about with the standby on? What if I wanted to use the preamp of the CL-400 into something else?
     
  19. BbbyBld

    BbbyBld

    Oct 13, 2005
    Meridian, MS
    It could be a bent tube socket that is making a poor connection depending on how you removed/replaced the tubes.

    You can't always tell by that.

    I'm thinking more and more that it's a loose connection on the power supply or on a wire coming from the power supply.

    You should not run a tube amp without a load on it with or without a signal, but with a signal is worse.

    If the amp does have a loose connection, a loose socket, or a failing power tube, it's likely that you will still notice the problem or cause more damage to the amp even if you are just using the pre, but...

    My Classic 400 is in pieces right now and I can't remember if the preamp will work with the amp on standby.

    If you want to use just the preamp, off standby, you can go out of the preamp out jack and stick a shorting plug into the power amp input jack. That will keep the power amp quiet. Then, hook up a load to the amp. You could use a cabinet, a dummy load, or just stick a shorting plug in one of the output jacks.
     
  20. mlwarriner

    mlwarriner Supporting Member

    Nov 8, 2003
    KC, MO, USA

    i tried to gently rock the tubes back and forth to get them out, not knocking them around too much and pulling them out as squarely as possible. to reinstall, i set them into the socket, turned them around until the alignment guide started in and then slowly rocked them back in, a little at a time.

    is there a grease or something that i should have used? some sort of dielectric compound or some such thing? i've never really done much inside tube heads before...