Problems with my tube amp last night...

Discussion in 'Amps and Cabs [BG]' started by brndn123, Oct 23, 2011.

  1. Maybe you guys can point me in the right direction as I'm a little confused as to whats wrong with my amp.

    Let me start off by saying my gig was last night (Saturday) and my tech is off on Mondays so the soonest I can get my amp looked over is Tuesday (insert Rebecca Black joke here).

    Anyways, I run a Fender Bassman 300, definitely the tube amp for me when it works. Hooked it up > turned it on > let it warm up for a good minute whilst grabbing my bass/tuning/etc > plugged bass in > poopy dull distortion on my clean channel. It got to the point where the master was on 4 (usually scary loud) and volume was significantly quiet and distortion more present. I swapped basses and changed cables, still poop sound. Gig was a short one so I ran the line out to the board and made due.

    Few notes: Had a bad tube about two months ago. Replaced the pair and biased with no issues until now. All power tubes seem to be clear, illuminated, fully plugged in. The Bassman has an LED for each pair of power tubes with GREEN indicating all things good and RED for a blown tube. Everything was green.

    So what do you guys think?

    Preamp tubes?
    Something more serious?

  2. will33


    May 22, 2006
    Possible preamp tube but check all the cables, bass batteries if they're active, etc. May also be dirty pots, jacks, etc. Perhaps a good cleaning is in order. Preamp tubes are cheap, plug-n-play, no biasing. Some stuff to try on your own. Use De-Oxit pot cleaner lube on every pot, jack, switch on there. Some contact cleaner in the tube sockets wouldn't hurt either. Give everything time to evaporated before powering it up.
  3. Blue


    Jun 19, 2004
    Southeast Penna
    Tube amps are great. The best part is you can swap tubes and get really interesting sound differences ... but tubes are mechanical things and more prone to breakage (that's the bad part - plus they weight a bunch, but you seem young!). I suggest swapping tubes (one at a time and all of them) and see if that fixed it 9sometimes you can see the filament is not glowing (and the tube is cold) ... or go to the dark side (as I have done) - and use mostly solid state - which is more reliable (and when they break, they break). If you insist on the Tubes - carry a full set or, ideally an entire separate rig - which is what th ebig boys are doing on stage. When you see two SVT's, it's more about reliability than sound volume.
  4. Oh also forgot to note...I purchased this amp brand new in June of this year and have a 6 year warranty :D
  5. will33


    May 22, 2006
    Then just use the warranty, taking anything apart will void it.
  6. Yeah I really love the thing. I can do just about anything I want with it, super versatile for both clean tones and tubey overdrive.

    As I mentioned, all the tubes seem to be clear and glowing. The preamp tubes have caps on them but I've never really experienced a bad preamp tube so I'm somewhat at a loss. I was using a Pbass so no preamp.
  7. B-string

    B-string Supporting Member

    Sounds like a preamp tube or at least the smaller 9 pin tubes. Could be first gain stage, tone stack, driver tube or PI. Don't expect the tubes to be covered for 6 years BTW. Just because tubes are "clear and glowing" means very little, that just means the heaters work and the envelope has not lost vacuum.
  8. waleross


    Nov 27, 2009
    South Florida
    Tech Time, end of story.......good luck . . . :cool:
  9. seamonkey


    Aug 6, 2004
    Fender has a great transferable warranty on the rest of the amp, but only 90 days on the tubes, and the warranty if vague if the bench charge for tube troubleshooting is covered. I hope it is. The tech should have a tube tester and be able to quickly diagnose if it's a tube.
  10. Thats exactly what I'm going to do
  11. Turock


    Apr 30, 2000
    That's not been my experience. In fact, just the opposite.
  12. anderbass


    Dec 20, 2005
    Phoenix. Az.
    brndn123, You could try plugging your bass into the amps fx-return (or power amp in) jack to completely bypass the preamp section. The amp wouldnt play as loudly this way but If you got a clean tone you'd be getting a good clue your problem was somewhere in the preamp section. And then If you still got your 'poopy dull distortion' tone you'd know for sure you had a poweramp issue.
  13. UPDATE* so I just plugged in the exact same bass into the exact same rig at my house to test it out. Sounded amazing! Could a bad outlet at the venue cause that much tone coloration?
  14. B-string

    B-string Supporting Member

    Simple direct answer YES! Low line voltage more than likely. ;)
  15. hmmm interesting. I should also point out me and the guitar player tripped the breaker twice during our set. I protected the tubes obviously, could the low line voltage from the outlet cause damage to my amp?
  16. B-string

    B-string Supporting Member

    Possible, some amps protect against low voltage (I remember a resent thread where a Genz would not fire up due to low line voltage and the player was not so happy). When voltage is low current needed goes up, not a good stress to place on any amp. More than likely your amp is still ok as it is newer, an older aged amp might over-stress worn components without low voltage protection. All amps should include low voltage shut down, would save trips to their techs IMHO.
    Low voltage and high current because of it, would cause the trouble you had. ;)
  17. Sweet, thanks for the info man. You're a lifesaver!
  18. B-string

    B-string Supporting Member

    Glad to help!
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