Results 1 to 16 of 16

Thread: No sound... Champ

  1. #1
    Forum Member melody's Avatar
    Join Date
    Jul 2002
    Location
    The third coast..!
    Posts
    3,667

    No sound... Champ

    My 74 champ has a problem just a slite hum no sound I did switch out the power tube,12ax7 and 5Y3 with no luck. I took the cassie out to look for burnt leaky caps all looks good to my untrained eye. Now I'm know amp tech but I do know how to use a volt meter/drain caps , anybody have any advice as to how to proceed trouble shooting? I can post pics if needed...

  2. #2
    Forum Member
    Join Date
    May 2008
    Posts
    616

    Re: No sound... Champ

    Is this hum from the speaker, or just from the on being on, as you could have popped the speaker.
    Since you have a volt meter, set it for ohms, unplug the rca jack that feeds the speaker and check for a open. A 4 ohm speaker will ohm test at around 3.2 ohms.
    If you know the speaker is ok, set your meter for at least a 500 volt DC setting an with the amp on hook it from ground to pin 3 of the 6V6 output tube and you should read at least 360 volts if the primary of the output transformer is not open.
    Report back on what you find.

  3. #3
    Forum Member melody's Avatar
    Join Date
    Jul 2002
    Location
    The third coast..!
    Posts
    3,667

    Re: No sound... Champ

    Speakers fine, I did the test you mention popped the fuse..

  4. #4
    Forum Member NTBluesGuitar's Avatar
    Join Date
    Apr 2006
    Location
    North Texas
    Posts
    5,820

    Re: No sound... Champ

    The electrolytic caps could still be bad even if there are no visual cues as to such. How old are they? Can you test capacitance with your equipment? I've overhauled several 70s SF amps and all the caps looked healthy, but replacing them fixed all issues (including the 'no sound' problem).

    Could also be a bad ground somewhere.

    Start with the simplest approach and then move to the more complex. Tubes, speaker, electrolytics etc. first.
    "...pray do not imagine that those who make the noise are the only inhabitants of the field;
    that, of course, they are many in number; or that, after all, they are other than the little,
    shriveled, meagre, hopping, though loud and troublesome, insects of the hour."

    -Edmund Burke

  5. #5
    Forum Member
    Join Date
    May 2008
    Posts
    616

    Re: No sound... Champ

    I guess you shorted the meter lead to more than just pin 3.
    If you replace the fuse and this time get no dc volatge on pin three, go to the end of the board and you will see where the a red wire comes off the can filter, test for dc volatge at that point.

  6. #6
    Forum Member NTBluesGuitar's Avatar
    Join Date
    Apr 2006
    Location
    North Texas
    Posts
    5,820

    Re: No sound... Champ

    The question of the electrolytics is still unanswered.

    How old are they? Why go into the transformer troubleshooting when the electrolytics haven't been ruled out yet?
    "...pray do not imagine that those who make the noise are the only inhabitants of the field;
    that, of course, they are many in number; or that, after all, they are other than the little,
    shriveled, meagre, hopping, though loud and troublesome, insects of the hour."

    -Edmund Burke

  7. #7
    Forum Member melody's Avatar
    Join Date
    Jul 2002
    Location
    The third coast..!
    Posts
    3,667

    Re: No sound... Champ

    NT, The store I bought it from said they where replaced it's been about two years.No I did not short it to any place other than the pin 3 and ground... I did replace the fuse and have it fired back up..

  8. #8
    Forum Member melody's Avatar
    Join Date
    Jul 2002
    Location
    The third coast..!
    Posts
    3,667

    Re: No sound... Champ

    I'm a I had the probe in the wrong receptacle on the meter. I did take a reading and I'm getting 411-13 V..Now what?

  9. #9
    Forum Member melody's Avatar
    Join Date
    Jul 2002
    Location
    The third coast..!
    Posts
    3,667

    Re: No sound... Champ

    Quote Originally Posted by steve25 View Post
    I guess you shorted the meter lead to more than just pin 3.
    If you replace the fuse and this time get no dc volatge on pin three, go to the end of the board and you will see where the a red wire comes off the can filter, test for dc volatge at that point.
    It reads 390V...
    Last edited by melody; 01-30-2009 at 11:26 AM.

  10. #10
    Forum Member melody's Avatar
    Join Date
    Jul 2002
    Location
    The third coast..!
    Posts
    3,667

    Re: No sound... Champ

    Quote Originally Posted by NTBluesGuitar View Post
    The question of the electrolytics is still unanswered.

    How old are they? Why go into the transformer troubleshooting when the electrolytics haven't been ruled out yet?
    NT, How do I test them? Ahhh I see you asked me the answer to my question already thanks.I dunno how I just have a simple volt /ohm meter...

  11. #11
    Forum Member melody's Avatar
    Join Date
    Jul 2002
    Location
    The third coast..!
    Posts
    3,667

    Re: No sound... Champ

    I have the schematic.. Doing some reading, here's a few pic's..

  12. #12
    Forum Member Don's Avatar
    Join Date
    Jul 2002
    Location
    Massachusetts
    Posts
    11,288

    Re: No sound... Champ

    Those electrolytics are old. That's the original can multi cap.

  13. #13
    Forum Member melody's Avatar
    Join Date
    Jul 2002
    Location
    The third coast..!
    Posts
    3,667

    Re: No sound... Champ

    Thanks Don! That's what I suspected.. Oh well I will have to do some sourcing and soldering...

  14. #14
    Forum Member NTBluesGuitar's Avatar
    Join Date
    Apr 2006
    Location
    North Texas
    Posts
    5,820

    Re: No sound... Champ

    Yep, all those white and silver circuit electrolytics are original, too. There's no way they replaced them two years ago...unless they replaced them with other '70s caps.
    "...pray do not imagine that those who make the noise are the only inhabitants of the field;
    that, of course, they are many in number; or that, after all, they are other than the little,
    shriveled, meagre, hopping, though loud and troublesome, insects of the hour."

    -Edmund Burke

  15. #15
    Forum Member
    Join Date
    May 2008
    Posts
    616

    Re: No sound... Champ

    Well at this point if you have that 413 volts on pin 3 of the output tube, and if both that tube and the 12ax7 are ok the amp should be playing for you.
    Next I would unsolder that red wire coming up thru that gromet and witha meter HOOKED up right to read ohms place it across that red wire that you unsoldered and pin 3, that blue wire and report back on what you read.
    Also for better tone, when you get the amp back up and running, clip the little brown cap out that is soldered across the output tube socket.

  16. #16
    Forum Member Kap'n's Avatar
    Join Date
    Sep 2002
    Location
    Where phony hippies meet
    Posts
    19,769

    Re: No sound... Champ

    Quote Originally Posted by steve25 View Post
    clip the little brown cap out that is soldered across the output tube socket.
    Yep, that's one of the CBS "tone sucker" caps.
    Several guitars in different colors
    Things to make them fuzzy
    Things to make them louder
    orange picks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •