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Peavey Classic 400

Discussion in 'Amps and Cabs [BG]' started by JustinC97, Dec 4, 2013.

  1. JustinC97


    Dec 4, 2013
    I just bought a Peavey Classic 400 bass head I took it apart with my father everything seemed fine then after putting it back together we ran it out to a 4Ω Guitar cab (sadly its the only cab I own currently) after leaving it on standby for 30 seconds to let the tubes heat up some. we turned off standby I tried playing nothing would come out after that we kept trying different inputs nothing but when we would take it off standby the speaker would react as if it is drawing power. any ideas on how to fix this?
  2. CL400Peavey

    CL400Peavey Supporting Member

    Nov 7, 2011
    Grand Rapids Michigan
    Tech time.
  3. Definitely.
  4. What exactly did you take apart-- and why?
  5. JustinC97


    Dec 4, 2013
    The guy who owned it before me lost the fuse cap and said some of the internal fuses might be busted so we took it apart to look at the fuses and install a new fuse holder on the back. the fuses were fine none were busted

    what do y'all think the tech might find?
  6. JustinC97


    Dec 4, 2013
    the took is out of the wood cab then took out the tubes while wearing latex gloves placed them on a towel, we opened it up to look at the board and the internal fuses
  7. You don't need to wear latex gloves when working with tubes, your fingerprints won't hurt them.

    Are you sure the cab and speaker cable works? Plug one end of your speaker cable into the cab, take a 9 volt battery and touch its terminals to the plug on the other end(one terminal on the plug's tip, one on the plug's shield). You should hear the cab make noise and the speaker cone itself should move. If nothing...the speaker cable or speaker is faulty, not the amp.

    Confirm the cab and cable work properly before doing anything else.
  8. BbbyBld


    Oct 13, 2005
    Meridian, MS
    Sorry, don't have much time. It's probably a blown IC on the preamp tube board.
  9. JustinC97


    Dec 4, 2013
    I just did the 9v battery test cable and cab work fine i use this cab for my mixer all the time. so that proves its a intenal problem, I know it isn't any of my cables. any ideas of what could be going on on the inside?
  10. Steve Dallman

    Steve Dallman Supporting Member

    Rather than just shoot willy-nilly, you should take a systematic troubleshooting approach.

    If this was on my bench, I'd put a signal into it with the amp plugged into a speaker. I would have a second, bench amp on. If no signal was passing to the speakers of the PV, I'd plug a cable into the preamp out/power amp in jacks. If sound passes to the speaker, then the power amp in jack switching is funky.

    If no signal passed, I'd run a cable from the preamp out to the bench amp (I use a small guitar practice amp) Is there sound there?

    If so, I'd patch my signal into the power amp in jack to see if the power amp is working.

    I use a CD or MP3 player for my signal source.

    This is the probe I made for tracing signals through an amp.


    I'd repeat all with the effects jacks.

    If there were still no signal, I'd take the amp apart and start by first confirming the correct voltages at the correct points.

    Then I'd again put a signal into the amp, and using a probe connected to my bench amp, grounded to the PV chassis, I'd follow the signal through the amp, from input jack to the speaker jack. Where it stops is the problem.
  11. BurningSkies

    BurningSkies CRAZY BALDHEAD

    Feb 20, 2005
    Seweracuse, NY

    ^^^ I'd put some weight behind this guy's opinion...He seems like he probably knows a lot about stuff.
  12. The first few tests (signal into preamp, signal out of effects loops) would be good for the OP to try.

    After that, though, he needs to take it to a tech. B+ is 675 volts in this amp with enough current to be lethal. The OP doesn't need to be poking around inside the amp.
  13. ^ He designs Peavey amps for a living, maybe even your one!

    You do realise poking around inside a tube amp is exceedingly dangerous even when you know what you're doing? They store lethal voltages long after being switched off.
  14. JustinC97


    Dec 4, 2013
    we weren't "poking" around. my dad use to work for alpine back in the late 70s to mid 80s and did car stereos for a good while. we were not going poking around inside the head like we're steve irwin
  15. Now you're really scaring me. Car audio has nothing in common with tube voltages. Did your Dad tuck one hand in his belt while probing? Gives you a fighting chance of surviving a 600v accident if the other hand isn't on the chassis.
  16. This could be something as simple as a phase inverter tube that's not plugged in securely, but of course it could be something more serious. A qualified tech will use some basic troubleshooting logic to figure this out. Someone that's not familiar with tube amps can hurt themselves or the amp or both.

    Where are you located? Perhaps someone on this forum is close to you and can help you out, either by looking at it themselves or recommending a good tech. If you were close to Nashville, for example, I could give it a quick look, I have all the schematics and am familiar with this amp since I have one.
  17. But big ass SS amps can have huge capacitors with big nasty amounts of current stored even after unplugging, so hopefully his dad did have some idea what he was dealing with.
  18. vbchaos


    Sep 5, 2011
    Groningen, The Netherlands
    Uncompensated endorsing user: fEARful
    Let me make something clear: A capacitor does NOT store current! Storing current is impossible - it's like trying to store velocity.
    A capacitor holds electric charge - you can say it stores energy. That'd be fine.
    Furthermore (unlike stated before), Voltage is NEVER lethal! I have had 5million Volts in my hands and I still breathe quite regulary.

    Please don't twist things, it gives electricians a migraine headache!

    Still the bottom line is correct - do not poke around in a tube head without knowledge of what you are doing. It takes 12-24hours to be sure that all components are discharged.
  19. JustinC97


    Dec 4, 2013
    True car audio really doesn't but big stadium shows like Led Zeppelin he's wired up the speakers before. my dad understand voltages
  20. JustinC97


    Dec 4, 2013
    well the only time we took apart it hadn't been plugged in, in well over a week