Silver Face Champ Too Bright/Trebly.

Discussion in 'Amp Tech Center' started by Blueguitar007, Apr 22, 2019.

  1. Blueguitar007

    Blueguitar007 TDPRI Member

    Posts:
    66
    Joined:
    Jan 30, 2011
    Location:
    KC
    I have a closet classic 70 Champ.
    Replaced elctrolytics and a blown resistor.
    Works great but just too trebly and bright.
    It sounds good with treble on about 1-3, but still not a lot of bottom end - it's pretty loud too.
    I have a 76 Champ that sounds really warm. I also sold a 73 Champ due to same thing , being too bright and trebly in the past so I don't want to give up on this one cuz I was kicking myself for selling the previous one.
    I've looked inside both my Champs and everything seems the same and ok.
    I also have swapped tubes and bought a m-f RCA lead to plug in different speakers. Right now I put in a Weber 8A125-O which should be darker, but it doesn't matter which speaker is hooked up.
    I'm more than happy to add a resistor or cap if I need to but the amp bias is something I haven't messed with on any amp.
    The amp ran super hot before I replaced the blown resistor but now the chassis is ok - it was getting hot - and I don't think anything crazy is going on now.
    I have seen a few videos working on Champs and I know they "run hot" on volts.
    A friend said swapping out a coupling capthat goes to the 6V6 will add bass but I would like some experienced opinions.
    Camera flash makes attached pic look weird but the board is looking good.
    Thanks all!
     

    Attached Files:

  2. Dacious

    Dacious Poster Extraordinaire

    Posts:
    6,222
    Joined:
    Mar 16, 2003
    Location:
    Godzone
    Errr, the chassis should get hot.

    Did you actually measure the voltage values, see what it's actually dissipating?

    It sounds like - to me - you may have cooled the bias a bit too far. Did you swap the bias cap when you did the others?
     
  3. schmee

    schmee Poster Extraordinaire

    Posts:
    5,294
    Joined:
    Jun 2, 2003
    Location:
    northwest
    Champs just sound that way to me, but evidently you have had one that didnt.. so I'm watching! My last one I put an Emi 820 speaker in which warmed up the top end, but still sounded like a megaphone!
     
    RyCo1983 likes this.
  4. Wally

    Wally Telefied Ad Free Member

    Posts:
    31,299
    Joined:
    Mar 17, 2003
    Location:
    Lubbock, TX
    Biasing is important in these amps.....and the power tube biases the amp. If two 6V6’s have drastically different operational specs, then the plate dissipation will vary greatly....thus the sonics will differ greatly.
     
    2 Headed Goat and Phrygian77 like this.
  5. corliss1

    corliss1 Friend of Leo's Platinum Supporter

    Posts:
    2,835
    Joined:
    Sep 13, 2008
    Location:
    Lansing, MI
    You mention electrolytics were replaced, but...was the cap can also replaced? You should also try and get more room between the large bias resistor and the cathode bypass cap there so the cap doesn't get cooked when that resistor gets hot.
     
    Wally likes this.
  6. Blueguitar007

    Blueguitar007 TDPRI Member

    Posts:
    66
    Joined:
    Jan 30, 2011
    Location:
    KC
    So get some space between resistors and caps? Never knew that..ok thanks for the tip!
     
  7. Blueguitar007

    Blueguitar007 TDPRI Member

    Posts:
    66
    Joined:
    Jan 30, 2011
    Location:
    KC
    I've tried swapping all tubes.. new tubes..etc... I do not know where to rad voltages..I saw where but I don't know what to do from there. Us there even a bias cap on these things? I bought a cap can 20x20x20x20 but haven't replaced it yet cuz there's no static and plenty of power. But I believe the cap can is almost fufty years old .
     
  8. Blueguitar007

    Blueguitar007 TDPRI Member

    Posts:
    66
    Joined:
    Jan 30, 2011
    Location:
    KC
    I've watched videos on measuring bias...ugh..gets complicated..but not sure on the remedy so gavenha measured .if you tell me where to measure ..ground and first resistor on power rail? I can do this. Btw the cgassch was getting HOT. Not hot. I mean burn your hand touching near power or rectumfrier tubes . It's even discolored on chassis. I threw those tubes out when replacing the 470 ohm resistor .
     
  9. Blueguitar007

    Blueguitar007 TDPRI Member

    Posts:
    66
    Joined:
    Jan 30, 2011
    Location:
    KC
    Chassis* the autocorrect on this site is crazy.
     
  10. corliss1

    corliss1 Friend of Leo's Platinum Supporter

    Posts:
    2,835
    Joined:
    Sep 13, 2008
    Location:
    Lansing, MI
    Electrolytics are good for 20 years. After that, they get swapped out without hesitation.

    Not entirely sure what you mean, but Champs are cathode biased with a big resistor and a cap, the ones I told you to get some distance between earlier.
     
  11. Blueguitar007

    Blueguitar007 TDPRI Member

    Posts:
    66
    Joined:
    Jan 30, 2011
    Location:
    KC
    Chassis was too hot to touch before in spots. Would live to bias the champ correctly...can't find a good vudeo on this .
     
  12. Blueguitar007

    Blueguitar007 TDPRI Member

    Posts:
    66
    Joined:
    Jan 30, 2011
    Location:
    KC
    If anyone could steer me a link on how to bias the champ I would be greatly appreciative..the dummy version preferably. I'll replace the cap can as I have that here already .Thanks!
     
  13. Blueguitar007

    Blueguitar007 TDPRI Member

    Posts:
    66
    Joined:
    Jan 30, 2011
    Location:
    KC
    Here are pics just for fun .The beat up one on right is the 76 that sounds warm and just friggin awesome. The 70 on right..I'm determined to replace everything if needed. I'm not selling off another pine cab champ.
     

    Attached Files:

  14. Milspec

    Milspec Friend of Leo's

    Posts:
    3,017
    Joined:
    Feb 15, 2016
    Location:
    Nebraska
    Is it still running the original speaker? Change it to a WGS 10C/S and your problems will likely be solved. I used to play through a couple of Gibson GA-5T amps that were painfully bright to my ears until I replaced the Jensens with the WGS speaker. The warmth it gave those amps was nothing short of a miracle and I could even run the treble dial up to about 7 without becoming brittle.
     
  15. Blueguitar007

    Blueguitar007 TDPRI Member

    Posts:
    66
    Joined:
    Jan 30, 2011
    Location:
    KC
    Fyi I installed a three prong cord too.
     
  16. galaxiex

    galaxiex Tele-Holic Silver Supporter

    Posts:
    856
    Joined:
    Jun 17, 2017
    Location:
    Edmonton, Alberta Canada
    Watch this...

     
    Paul in Colorado likes this.
  17. RyCo1983

    RyCo1983 Tele-Afflicted Silver Supporter

    Posts:
    1,609
    Joined:
    Aug 15, 2012
    Location:
    Central PA
    I'll second the Eminence comment.
    The 820H hemp coned speaker is a huge improvement.
     
  18. Blueguitar007

    Blueguitar007 TDPRI Member

    Posts:
    66
    Joined:
    Jan 30, 2011
    Location:
    KC
    No..In my OP I said I put in a weber 8A125-O a darker speaker..but it's new. Original Oxford 8ev was WAYYY to bright - agreed.
     
  19. Whatizitman

    Whatizitman Tele-Afflicted

    Posts:
    1,640
    Joined:
    Feb 18, 2018
    Location:
    WV
    My SF Champ was the first amp I attempted any measurements. Get comfortable with that before even attempting to bias it.

    Start with robrob’s intro, based on the Tweed Champ, which is not too different than a BF/SF Champ. Then read his chapters on safety, bias, and startup.

    https://robrobinette.com/How_Amps_Work.htm

    Watch this. Then watch it again. Then make sure you are familiar with high voltage safety. Then, and only then, take measurements, and write them down.





     
    Blueguitar007 likes this.
  20. peteb

    peteb Friend of Leo's

    Posts:
    3,790
    Joined:
    Apr 25, 2003
    Location:
    Cascadia

    Just measure the resistance of your 470 ohm cathode resistor, then measure the idle DC voltage across it.


    That’s most of it.

    Then if you can measure the plate voltgae, also DC, that’s it.


    Calculate the current thru the resistor and multiply times the plate voltage minus the cathode voltage.



    Most likely, it will be in the acceptable range.
     
    Blueguitar007 likes this.
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.