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Fender Bassman 300 Pro - No output

Discussion in 'Amps and Cabs [BG]' started by glummoon, Jan 6, 2012.

  1. glummoon


    Jan 5, 2012
    Recently my amp has powered up, and all of the controls on the front look normal with the exception of the Power LED. You can turn on the EQ, compressors, see input level via the LED, but there is no output. I am about to crack it open to see if there is something obviously blown, and I wanted to toss this out to the community to see if anyone had any ideas as to what might be going on with it.

    Thanks in advance!

  2. charlie monroe

    charlie monroe Gold Supporting Member

    Feb 14, 2011
    Buffalo, NY
    Welcome to talkbass, Jon.

    Bump for a first time poster that needs some help.
  3. fenderphil


    Sep 1, 2006
    Houston, TX
    Check your fuses...

    Their location and ratings should be explained in the manual.

    Also, There's LEDs by the tubes, and they glow different colors to indicate problems.

    Have the tubes been biased?
  4. jastacey


    Feb 8, 2009
    I take a shot at this, my first question is when the amp is in stand-by, are the Led's glowing red? ... they change to green when you switch the amp out of stand-by, also there are some fuses by the power tube sections ...... did you check the mute switch?
    There are no internal fuses on that amp, and thosep amp store 600+ volts in the caps ....so be very careful if you decide to open the amp up .... you really need to be pretty experianced to work on those amps ... IMHO
  5. glummoon


    Jan 5, 2012
    I have checked the fuses in the back of the amp and they look good.

    The LEDs do go from Red to Green when the amp is brought out of Standby, but today I am noticing that none of the tubes appear to be glowing. I am pretty sure they were the the other night when I first noticed the issue, but they definitely are not now.

    I had a run in with the Tuner Only switch the other day(it being on and me wondering why there was no sound), so that was one of the first things I checked.

    I believe these are the original Fender tubes that came with the amp, or an OEM Fender set, and I haven't had any work done on the amp since it was delivered two years ago.

    Thanks for the help! I have a tribute show to play on the 14th, so any help in getting it back on the road is greatly appreciated.


    When reseating the tubes I decided to try turning it on with just one pair of power tubes in place and an odd thing happened. All of the LEDs were Red, as I would expect, but when I came out of Standby they all turned green even though there were only two tubes installed. I am not sure if this is normal, or sheds any light on the situation, but I thought I would mention it.
  6. the 300 PRO is quite a complex amp. If you can get it to a tech then do so.
  7. glummoon


    Jan 5, 2012
    Indeed! I have seen pictures of the guts and at this point I don't have any plans of opening the innards on my own. It makes my 70s Bassman look like something a caveman built.

    At this point I am hoping to get some information that could help a professional perform the repair quickly.
  8. glummoon


    Jan 5, 2012
    I got up the guts to pull the amp out of the chassis today and found more fuses. I think I will replace all of them in hopes that one is actually bad. All of those 450v caps are pretty fearsome looking.

    By the way, listened to the Monobrow stuff. Kept me going all the way through, thanks for the advice and the soundtrack for working on this.
  9. charlie monroe

    charlie monroe Gold Supporting Member

    Feb 14, 2011
    Buffalo, NY
    Hey Jon, not for nothing, but bassboysam's advice was to take it to a technician.
    I appreciate that you are curious, or maybe don't have a budget, but you just said that you can't tell if a fuse is bad or not.
    Take it to a tech.
  10. I agree fully with Sam and Charlie's advice. A tube amp of that class is not something an untrained person should be messing with. trust me the price you pay a tech will be much less than your life is worth!!!

    Take it to a tech. If the problem is simple his bill will be small.
  11. Yes that amp can be VERY unforgiving to noob mistakes, even small ones can mount a huge repair bill. Pay a little now or maybe A LOT later?
  12. Glad the album came in handy :D.

    Hopefully you can get the amp sorted out soon, curious to see what the problem is .
  13. glummoon


    Jan 5, 2012
    I did get the fuses tested using a D cell and a multimeter. I will get in touch with the tech I have had recommended tomorrow and throw myself on his mercy.

    In the meantime I have dusted off my old Bassman 135, and so far it has performed better than I could have hoped at practice tonight.

    Thanks for all of the help, and I will be in touch with a resolution once he sorts it out.

    Thanks again!
  14. WingKL


    May 12, 2007
    Uh, you shouldn't need a D cell to test fuses if you have a multimeter. Most multimeters have a ohms resistance setting or a continuity tester you could use to see if the fuse is intact.
  15. glummoon


    Jan 5, 2012
    Hey folks, just got my amp back from the shop and I am preparing to give it a test run. They said one of the transformer wires had been rubbing against a screw and had shorted out. Luckily the transformer didn't melt down and they were able to get everything up and working in less than 24 hours. They were surprised that no one got shocked and that the transformer survived the ordeal.

    They said that Fender had put out a suggested modification raising some of the capacitors and resistors by an order of 10, i.e. some of the 47 micro farad to 470 and some resistors from 3.3 ohms to 33 ohms. This is supposed to combat some of the heat issues that the amp experiences. I am going to hold off on this until after the show, but I want to keep this amp until I am old and gray, so I will be getting it done.

    Thanks again for all of the help, and I hope this helps someone else in the future.

  16. Hey guys thanks for the post - anyone got a copy of recommended mods from Fender? I just bought one of these and its running way too hot.

  17. Herxheimer


    Oct 5, 2015
    Are there any updates on this Fender mod suggestion?

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