1. Win a Broadcaster or one of 3 Teles! The annual Supporting Member Giveaway is on. To enter Click Here. To see all the prizes and full details Click Here. To view the thread about the giveaway Click Here.

SF Champ blown Output Transformer causes?

Discussion in 'Amp Tech Center' started by goldenhound, Sep 27, 2016.

  1. goldenhound

    goldenhound TDPRI Member

    Posts:
    78
    Joined:
    Jun 2, 2010
    Location:
    The Great NorthWest
    This seems like a problem searching for a solution. How do others keep a shorted power tube from destroying the OT? Rob Robinette (RobRob), suggested putting a MOV between the 3rd pin/6v6 and the B+1 supply rail earlier in the thread. I feel really stupid asking this, but is that what his mod does?
     
  2. RLee77

    RLee77 Friend of Leo's

    Posts:
    4,314
    Joined:
    May 15, 2016
    Location:
    Nevada
    It could be excessive current thru the OT, or it could just as easily be a big flyback voltage spike arcing thru the insulation, caused by a faulty component or connection. At this point I would check every component and connection in the power supply and output stage.
     
    Darkness likes this.
  3. Darkness

    Darkness Tele-Afflicted

    Age:
    52
    Posts:
    1,131
    Joined:
    Apr 7, 2016
    Location:
    Stygian Gulf
    Sure. The schematic shows a 25uf/25v. I replaced it with a Sprague 25uf/50v. The higher voltage does not affect tone, it is insurance against today's higher wall voltages.
     
    goldenhound likes this.
  4. Ten Over

    Ten Over Tele-Holic

    Posts:
    672
    Joined:
    May 13, 2015
    Location:
    Central California
    The consensus of opinion for the two main causes of OT failure seems to be tube short and flyback voltage. The MOV neutralizes the flyback voltage problem. If you are going to order MOV's from Mouser, you might consider getting a fuse holder and some fuses to neutralize the tube short problem. Littelfuse 3540001 is a single-gang chassis mount 3AG fuse holder with solder lugs that works great for internal fusing. Connect the red lead from the OT to one side and a wire to the power supply to the other side. Bel makes fuses that are much cheaper than Littelfuse or Eaton, but I have never tried them so I don't know if they are any good.

    I'm not really sure how many mA's a 6V6 plate can take down at full overdrive, but you would want a fuse that could at least handle that. On the other hand, you don't want one that allows enough current to blow the OT. I'm thinking 125mA for starters and that would be a fast blow fuse.

    A piece of equipment that is real handy if you work on faulty electronics very much is an Eagle 441-R364-GR In-Line Fuse Holder with alligator clips on the wires. It allows you to try things without permanently installing an internal fuse.

    It occurs to me that if you are worried about flyback voltage, maybe you should solder the secondary leads together for initial testing.
     
    goldenhound likes this.
  5. robrob

    robrob Poster Extraordinaire Ad Free Member

    Posts:
    7,972
    Joined:
    Dec 29, 2012
    Location:
    United States
  6. goldenhound

    goldenhound TDPRI Member

    Posts:
    78
    Joined:
    Jun 2, 2010
    Location:
    The Great NorthWest
    What if I were to say the Champ is now working? That the assumed fried OT appears to be operational with no continuity between Red wire and chassis, and between Blue wire and chassis? And that the OT only gets barely above room temperature - barely noticeable?
     
    t guitar floyd likes this.
  7. robrob

    robrob Poster Extraordinaire Ad Free Member

    Posts:
    7,972
    Joined:
    Dec 29, 2012
    Location:
    United States
    Sweet. Somewhere along the line the problem, probably a short, was fixed. Congrats on getting it up and running.
     
    goldenhound likes this.
  8. jonrpick

    jonrpick Friend of Leo's

    Posts:
    2,267
    Joined:
    Mar 17, 2014
    Location:
    Marietta, GA
    Then, without going back and re-reading the entire thread, I'd have to wonder if the original OT was actually good.

    Either way, that's good news.
     
    Tone Chase likes this.
  9. slider313

    slider313 Tele-Afflicted Silver Supporter

    Posts:
    1,390
    Joined:
    Jan 6, 2011
    Location:
    NC
    So, what was the actual problem?
     
  10. t guitar floyd

    t guitar floyd Tele-Holic

    Age:
    73
    Posts:
    938
    Joined:
    Feb 4, 2016
    Location:
    sw US
    What if you were to say? I think you should go ahead and say it and see what happens . . . or leave us all hanging and wondering . . . :confused: :D
     
    goldenhound likes this.
  11. goldenhound

    goldenhound TDPRI Member

    Posts:
    78
    Joined:
    Jun 2, 2010
    Location:
    The Great NorthWest
    If I hadn't actually had my hands on it, I'd scarcely believe it. The brown wire on the ClassicTone OT is for amps that require a 5k. The Champ uses the Blue wire, the 8k tap. Here's what I believe happened.

    The Champ has a hard plastic grommet that all the wires of the OT have to pass through. The original design uses an OT with 4 wires. The ClassicTone OT has 6 wires. I (stupidly) tried to put 6 wires through that grommet which provided quite a lot of friction between the wire insulation and the grommet even though I used a silicone spray to ease passage. Somehow, in the process, the brown wire must've caught on the edge of the hard plastic and stripped away 1mm of the insulation, exposing the wire. It was discovered when I went to pull the OT to send back to Tube Depot. Not sure how, but I'm thinking that the stripped wire shorted to the chassis. I clipped the brown wire as there was really no need for it in the first place. It will never be used.

    Hooked everything back up, and using the light bulb limiter, plugged it in. The first thing I noticed was no hum. I had to check the speaker connector, and volume to make sure nothing was wrong!

    The 60 watt bulb showed semi-bright, and then went very dim, and fluctuated as the amp idled. I left it on for a couple of minutes, monitoring the tubes and holding the OT to make sure it didn't get too hot.

    I then took the limiter out of the loop and played with the volume. Blessed silence. Played a couple of chords and all sounds fine. I did notice a crackle as I played with the controls, and tapped on the chassis. Caps? Corrosion in the pots? Maybe both?

    Obviously, you all have been great. Many thanks to Ten Over, and his dogged persistence in walking me through all of this. You all have had both hands tied behind your back, and a blindfold in helping me diagnose this. I want you to know how grateful I am. I also want to thank RobRob for his references to protection circuits. I will enjoy applying those mods.

    And lastly, I don't trust that OT. I'm bundling the tubes up to send back for testing. I will be ordering a new OT when funds permit.
     
  12. corliss1

    corliss1 Friend of Leo's Platinum Supporter

    Posts:
    4,457
    Joined:
    Sep 13, 2008
    Location:
    Lansing, MI
    Very cool - glad you were able to track this down!
     
    goldenhound likes this.
  13. Darkness

    Darkness Tele-Afflicted

    Age:
    52
    Posts:
    1,131
    Joined:
    Apr 7, 2016
    Location:
    Stygian Gulf
    Order the new OT from Allen Amplification. He's got a drop in replacement that is fantastic. It's a US made Heyboer transformer that costs 45 bucks. The part is T08C. I replaced a stock OT that was mushy sounding with the Allen OT and that champ now sounds better than my other champs. Highly recommended!!
     
    goldenhound likes this.
  14. Commodore 64

    Commodore 64 Friend of Leo's

    Age:
    45
    Posts:
    4,182
    Joined:
    Mar 1, 2010
    Location:
    Kent, OH
    Emphasis mine. Back on page 3. Just sayin'...:p
     
    goldenhound likes this.
  15. RLee77

    RLee77 Friend of Leo's

    Posts:
    4,314
    Joined:
    May 15, 2016
    Location:
    Nevada
    Yeah but that just takes care of the *ends*... you didn't say anything about the *middle* part of the extra leads.:D
     
    goldenhound and Commodore 64 like this.
  16. Ten Over

    Ten Over Tele-Holic

    Posts:
    672
    Joined:
    May 13, 2015
    Location:
    Central California
    Now that is how the light bulb should behave for a good amp.

    That plastic grommet is open to the chassis on the inside, so it is very possible to have frayed wires touch the chassis. The suggested last test in reply #82 would have caught the lead short.

    I was curious about the original OT, also. None of the Champ OT's that I've seen have vent holes. There are holes where the leads come out. Is it possible that the sparks observed were actually lead to chassis? Does the primary have any resistance across it or to the case? Are there any visual signs of arcing?
     
  17. goldenhound

    goldenhound TDPRI Member

    Posts:
    78
    Joined:
    Jun 2, 2010
    Location:
    The Great NorthWest
     
  18. goldenhound

    goldenhound TDPRI Member

    Posts:
    78
    Joined:
    Jun 2, 2010
    Location:
    The Great NorthWest
    Is that the OT that uses a plastic wrap instead of paper? Maybe it wasn't that OT, but I heard four OTs in a shootout (probably sponsored by Magnetic Components), and the Heyboer did sound pretty darn good. It was neck and neck with the ClassicTone which uses a paper wrap and purports to faithfully reproduce the Champ OT. It's also $17 cheaper which is why I went with it in the first place.

    Dadgum it, Darkness - I was perfectly happy in my blissful ignorance! :)
     
  19. connuchar

    connuchar Tele-Meister

    Posts:
    177
    Joined:
    May 30, 2006
    Location:
    phx az
    a good rectifier tube is crucial, eye put a new one in[do not remember the brand] and it died after 3 or 4 plays [not long plays either] had to put the old rectifier tube back in biasing the 6v6 helped alot on mine
     
  20. Commodore 64

    Commodore 64 Friend of Leo's

    Age:
    45
    Posts:
    4,182
    Joined:
    Mar 1, 2010
    Location:
    Kent, OH
    Hey man don't fixate on this. I've roached so much stuff, ignored so much good advice, came in here and made blatantly incorrect comments/assumptions. It's all about learning. You learn more when you do something wrong than when you do something right (well, I do at least).

    I'm finding that learning is a combination of consuming info, trying and failing, and revisiting the info I've consumed...and sometimes I interpret the same info differently or understand it more.

    That's what I love about internet forums. Most of us know something. And all of us want to tell you about it, in a way that makes sense to us. And with enough people doing that, some of it is bound to make sense to you. You know 5 different ways to say the same thing...some people understand the first, others the fifth, and some people understand snippets of all five. And so we can all learn and grow together. I guess that's pretty corny. But don't be afraid to fail or be wrong. I'm embarrassed of many of my posts just 2 years ago. Sometimes much less than that! But another way to look at it, is that it's a great documentation of how much I've learned, and how much support this community provides to us all.

    And BTW, the Cap Can, rectifier tube, or power tube failure...this could be do to a million factors, many of which are simply age and use. And the fact that the B+ in those amps is pretty high, too high really (which is why some people put a dropping resistor in there).

    Look here: http://www.tdpri.com/threads/69-vibrochamp-innards-pics-advice.456149/#post-5519700

     
    Last edited: Oct 27, 2016
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.