Is this 6V6GT Tube Bad?

Discussion in 'Amp Tech Center' started by Tenderfoot, Nov 28, 2017.

  1. Tenderfoot

    Tenderfoot Tele-Meister

    Age:
    72
    Posts:
    371
    Joined:
    May 8, 2014
    Location:
    Katy, TX
    My Tone King Imperial Mark I blew a fuse while in standby mode. I understand this can be caused by a failed power output tube so I pulled the two 6V6EH (made in Russia) to see if anything obvious could have caused the fuse to pull enough current to open the fuse (2A250VP Slow Blow 313). The only thing that caught my eye was something I never noticed before. Both tubes had a brownish deposit on the inside wall of the socket base (see attached photo). I have looked at these tubes before and think I would have noticed something like this so I'm thinking that something either in the chassis or the tubes themselves went south. This is a class A self biasing amp.

    I'm going to get a replacement fuse(s) tomorrow and another set of power tubes, so any advise comments would be most welcome.

    Thanks! IMG_1911.JPG
     
  2. uriah1

    uriah1 Doctor of Teleocity Ad Free Member

    Posts:
    19,851
    Joined:
    Feb 12, 2011
    Location:
    Around
    fyi. Replace phase inverter tube .. a bad one took out a plate resistor on me once...
    could be anything though.might be amp tech time. Doubt 2 power tubes bad., but, you never know.
    Wish you luck.
     
  3. corliss1

    corliss1 Friend of Leo's Platinum Supporter

    Posts:
    3,043
    Joined:
    Sep 13, 2008
    Location:
    Lansing, MI
    I don't know if that is necessarily bad or not. Pull all the tubes, put in the fuse. Put tubes back in one at a time until the amp works or the fuse blows. That will tell you if it's a tube. If it's not a tube, it's tech time.
     
  4. Tenderfoot

    Tenderfoot Tele-Meister

    Age:
    72
    Posts:
    371
    Joined:
    May 8, 2014
    Location:
    Katy, TX
    Problem solved! It turned out to be the rectifier tube that was blowing the fuse. I went to Kats Guitar Store in Spring TX this morning and got some 2A250V Slow Blow fuses (you can get a pack of 5 for $10 plus tax) and had the 6V6 tubes tested - they were good. Going back home I got to thinking about the comment made by the store repair tech that with the amp in standby there was no plate voltage and shouldn't be a current draw such as red plating. With this in mind, I replaced the fuse and put the amp in standby mode. After 10 seconds the power light started to slowly dim until it went completely out. Checking the fuse it was found to have blown. With my thinking cap on a little straighter than yesterday, I looked at the schematic and found that the rectified tube input was on the secondary of the input transformer. Having a spare rectifier tube, I crossed my fingers, installed it and turned on the power with hopes it was the rectifier tube and not the input transformer. As stated at the beginning of this post, it turned out to be a bad rectifier tube causing the fuse to blow.

    I called the music store tech and let him know and am posting my troubleshooting findings here; perhaps it might be of help to someone else in the future when a fuse blows with amp in standby mode.

    Take Care
     
    uriah1 likes this.
  5. corliss1

    corliss1 Friend of Leo's Platinum Supporter

    Posts:
    3,043
    Joined:
    Sep 13, 2008
    Location:
    Lansing, MI
    There's a reason a lot of us on here swear by NOS rectifiers. That's one tube I pretty much only do NOS.
     
  6. alnicopu

    alnicopu Friend of Leo's

    Posts:
    3,806
    Joined:
    Oct 3, 2009
    Location:
    The city
    Totally agree. It is worth paying more for a good solid NOS rect. Get it and pretty much forget it.
     
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.


  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.