SF champ amp book

Discussion in 'Amp Tech Center' started by goldenhound, Mar 30, 2020.

  1. goldenhound

    goldenhound TDPRI Member

    Posts:
    76
    Joined:
    Jun 2, 2010
    Location:
    The Great NorthWest
    Greetings!

    I'm looking for a in - depth tech book on the BF/SF (aa764 circuit) Fender Champ.

    This is not for a Vibro Champ, just a plain old vol, bass, treble, vanilla Champ.

    A detailed book that fully breaks down the circuit and explains what the caps, resistors, tubes, do in the circuit. What the voltages should be at the tubes, filter caps, etc. Some troubleshooting information would be awesome.

    A book that will let me check the health of the amp circuit.

    Not asking too much, right??
     
  2. King Fan

    King Fan Friend of Leo's

    Posts:
    4,994
    Joined:
    Jan 1, 2013
    Location:
    Salt Lake City
    I admire your plan to learn about that specific amp, but you may do better trying to find books about tube amps in general, zooming in on Fender, '60s, single-ended, low-power, etc. Rob's great "How Amps Work" page, with its focus on the mostly-similar 5F1, would be a great start.
     
  3. SnidelyWhiplash

    SnidelyWhiplash Friend of Leo's

    Posts:
    2,503
    Joined:
    Jun 18, 2009
    Location:
    Hoggtown, KY.
    I don't think that such a specific book exists. Not much demand for what was originally a " student " amp. Who would have thought that these would become so desirable?
     
    goldenhound likes this.
  4. Salty_critters

    Salty_critters TDPRI Member

    Posts:
    14
    Joined:
    Sep 16, 2018
    Location:
    Virginia


    Not exactly a comprehensive breakdown, component by component, but Terry and his videos pertaining to Silverface Champs helped me quite a bit when I was restoring my 75 Champ. Uncle Doug, also a YouTube channel with tube amp-related videos, has some great information on small, single ended amps like the Champ. Grab a schematic and start studying.

    Sorry it's not a book. Next best thing perhaps? :)
     
  5. noname_dragon

    noname_dragon Tele-Meister

    Posts:
    357
    Joined:
    Jan 13, 2010
    Location:
    North east coast
    Fenderguru.com has some interesting info on Champs and other Fender amps.
     
    muscmp and goldenhound like this.
  6. corliss1

    corliss1 Friend of Leo's Platinum Supporter

    Posts:
    3,989
    Joined:
    Sep 13, 2008
    Location:
    Lansing, MI
    No such thing exists, as has already been mentioned. What are you looking to know? I've been recommending this guy for years now as it really breaks down every part of the amp and what it does.

    https://www.amazon.com/dp/148039288X/?tag=tdpri-20

    It does include a walk through of the tweed Champ.
     
    Salty_critters and King Fan like this.
  7. trxx

    trxx Tele-Afflicted

    Age:
    42
    Posts:
    1,053
    Joined:
    Dec 6, 2019
    Location:
    Between reality and imagination
    I would call Dave Hunter's walkthrough of a champ more of a skating over. No such thing really exists as far as I know. It's a good idea though.

    Goldenhound, you'll have to piece it together like everyone else. Rob Robinette's site, Uncle Doug's videos, and D-Lab's videos are probably the best stuff you will find.
     
    goldenhound likes this.
  8. goldenhound

    goldenhound TDPRI Member

    Posts:
    76
    Joined:
    Jun 2, 2010
    Location:
    The Great NorthWest

    Well said, like others have commented. I am a student of Uncle Doug (he's my favorite).

    D-lab has gotten the closest with his video about checking the health of your Champ with voltage benchmarks, and a methodical step-thru. Probably the most thorough check up on a Champ I've seen so far.

    Rob Robinette's treatment of the 5F1 build is what I'm currently going through to see if I can get a better grasp through the direct ancestor to my SF Champ.

    I've been chasing definitions of terms like , bypass capacitors, and cathode resistors. Uncle Doug is a good reference for some of that, as well as Google.

    I'm still holding out hope that there might be a site that can condense this information.

    If I were a writer, I'd consider doing a book like this. I'd consider doing a series of books like this!

    Thanks for weighing in, trxx.
     
  9. goldenhound

    goldenhound TDPRI Member

    Posts:
    76
    Joined:
    Jun 2, 2010
    Location:
    The Great NorthWest
    I'll spare you the long story, and cut to the vague summary. My apologies for the crudeness of the description. The 6v6's tiny orange light just above the base of the tube (filament light?) is jumping, literally elongating (about 1 or 2 mm) when I strike a chord. It looks like a digital VU meter.

    OK, here's SOME of the long story.
    I had unhooked the tone stack by unsoldering the15k resistor to ground from the bass tone pot but I'm not sure if that has anything to do with it.

    The JJ tube I have in there is a replacement for my cherished original Amperex that was in there when I bought the chassis from an electronic surplus store in Northridge, CA in '84. The Amperex bottle literally broke from the base of the tube. I thought it might have something to do with voltages in the tube, but I'm not at all sure.

    I claim no sure knowledge of electronics other than how to solder, what i've picked up chasing this problem, and some rudimentary projects and kits. I've dropped trig classes twice! So, this is obviously a hobby and not my line of work.

    Due to other problems, I have replaced the filter caps and bypass capacitors, and a blown output transformer. So far my quest for knowledge has been acquired by destroying stuff. My poor Champ! I'd love to try to put this little amp back in operation but I'm going to make sure that I check to make sure that everything is as it should be.

    Suggestions on tech manuals, and videos as well as advice is all appreciated. I'll try to take any jokes at my expense with a good sense of humor! Thanks in advance.

    Rob
     
    Last edited: Mar 31, 2020
    Salty_critters and Tele Slacker like this.
  10. goldenhound

    goldenhound TDPRI Member

    Posts:
    76
    Joined:
    Jun 2, 2010
    Location:
    The Great NorthWest
    Been a fan of Uncle Doug for a while now. His series on amp components have been helpful. Still going through his library .

    Thanks for the advice on Terry's videos. I'll definitely take a look!

    Regards
    Rob
     
  11. goldenhound

    goldenhound TDPRI Member

    Posts:
    76
    Joined:
    Jun 2, 2010
    Location:
    The Great NorthWest

    Agreed. Thanks!
    Rob
     
    SnidelyWhiplash likes this.
  12. goldenhound

    goldenhound TDPRI Member

    Posts:
    76
    Joined:
    Jun 2, 2010
    Location:
    The Great NorthWest
    Agreed. Studying his kit instructions for his 5F1.

    Thanks!
     
  13. King Fan

    King Fan Friend of Leo's

    Posts:
    4,994
    Joined:
    Jan 1, 2013
    Location:
    Salt Lake City
    It sounds like you're having a specific problem with the amp, or a series of problems and questions that came up as it started to go through tubes, transformers, and so on?

    Understanding the amp is still a good goal, and how-it-works knowledge is out there. But *how-to-diagnose* and *how-to-fix* knowledge is not as easy to put in books. A college physiology prof knows all about how the kidney works -- but you don't go to him when you get a kidney stone.

    If you're having amp problems, the traditional route on the forum is to start a thread (this forum is perfect) describing the symptoms, the amp (specifically, what year -- matters with Champs), any prior revisions -- and current voltages, good pics, and so on. Then we'll send back about a dozen guesses and suggestions and tests to try, and we go forward from there. :)
     
  14. corliss1

    corliss1 Friend of Leo's Platinum Supporter

    Posts:
    3,989
    Joined:
    Sep 13, 2008
    Location:
    Lansing, MI
    I would just try a new power tube with the scenario described above.
     
    King Fan likes this.
  15. muchxs

    muchxs Doctor of Teleocity

    Posts:
    13,118
    Joined:
    Aug 14, 2004
    Location:
    New England
    I'm a writer among other things. I even have a background in technical writing.

    I'm too busy building amps and chasing The Elusive Green Yankee Dollar to mess with anything else.

    Besides, one camp would complain I didn't go into enough technical detail, that I didn't show pages and pages of long hair math and so on.

    After all it's been damn near half a century since I went to school for this stuff.

    The other camp would complain bitterly that I whizzed everything over their heads.

    My would be best seller would surely and universally be panned.

    :rolleyes: :rolleyes: :rolleyes:

    Oh, yes. It has everything to do with it.

    Look up the 6V6 tube data sheet. It's easy. Go to Google, type in "6V6 tube data sheet" and make the best sense you can of what you get.

    After all, we didn't have The Magic Internet, we didn't have Google, we didn't even have hip tube amp books when I first attempted to electrocute myself. What I do have is piles of Marshall and Fender schematics I Xeroxed on a crappy copy machine that was running short on toner. My first epiphany:

    All Marshalls look alike.

    They did in 1978.

    For reals!

    :cool: :cool: :cool:

    Pay attention here:

    Max plate voltage on your 6V6 tube is listed as 300 volts on every old tube data sheet I can find. If you risk electrocuting yourself and measure the voltage at Pin 3 of your 6V6 tube (the plate) you'll likely find your (plate) supply voltage is over 400v. No tube data sheet ever said that was a good idea.

    But... it works. It works until you do the tone stack lift. The combination of elevated supply voltage and a little bit more gain often makes 6V6 tubes arc. I'd expect JJs to hang in there but what do I know?

    That's probably what killed your output transformer. Supply voltage needs to go through the transformer to get to the tube.

    If Thor is tossing little lightning bolts something is gonna get whacked.

    Oh, good. You must have got a deal on it in '84. I've mostly used up the stack of old Champs I accumulated. I'll be happy to trade a thin wedge of green foldable for your chassis.

    Problem solved!

    :cool: :cool: :cool:

    Seriously, if you want to keep your tubes from arcing you need to reduce your supply voltage. There are several ways to do that. You can use zeners, add an extra filter stage and a resistor in the power supply or swap to a power transformer with less supply voltage. I like using an upgraded PT. It's a simple swap.

    Zeners or resistors convert useful power into useless heat.

    I'm a machinist among other things. I managed to miss trig every time it came up. As long as I'm making round parts on the lathe or square parts on the mill I get by o.k.

    I blew up a few myself on the steep part of my learning curve, mostly power transformers. I've been fixing stuff other people have blown up for a long time now.

    We have a saying,

    "We don't need no stinkin' schematic!"

    although a schematic sure is handy every so often.


    They're teachin' the kids "Common Core Math", whatever that is. Girlfriend is a scientist and a researcher. She thinks Common Core is goofy. I'm glad I don't have to mess with it.

    Girlfriend's math is always right. People's lives depend on it.


    If you couldn't shoot and cut commercials using your phone I would still be employed doin' video and film production.

    Tellin' you that to tell you this:

    Just about anything you want to know is a screen or two away on The Magic Internet. The only difficulty is discerning information from BS. I grew up on a farm. I've never had a problem identifying BS when I see it.

    :D :D :D
     
    Last edited: Mar 31, 2020
  16. goldenhound

    goldenhound TDPRI Member

    Posts:
    76
    Joined:
    Jun 2, 2010
    Location:
    The Great NorthWest
    ]
    Good suggestion. Thanks!
     
  17. Whatizitman

    Whatizitman Friend of Leo's

    Posts:
    3,441
    Joined:
    Feb 18, 2018
    Location:
    WV
    Your book just spoke. Bookmark it.
     
  18. goldenhound

    goldenhound TDPRI Member

    Posts:
    76
    Joined:
    Jun 2, 2010
    Location:
    The Great NorthWest
    Well, I do have a new JJ 6V6 from EuroTubes that is installed in it now, due to my old Amperex bottle being cut cleanly from the base of the tube when this whole thing started. I have powered the amp on only to try to trouble shoot it.

    As has been suggested, I will next start a new thread, post a summary of changes if I can remember the sequence of events that occurred about a year ago, and the voltage.

    Muchxs suggested where to grab the voltage for the 6v6 off of pin 4. Am I to assume that the positive should be on pin 4, and the negative on the chassis for ground to take the voltage?

    If there are other voltages I should include, I would be happy to supply them, if only someone would be so kind as to tell me in detail what pins to check, and /or where to put the little red probe and the little black probe from my dmm, as a courtesy.

    I am not an imbecile, but I'm trying real hard to work up to it.

    Thanks!
     
    Last edited: Mar 31, 2020
  19. Whatizitman

    Whatizitman Friend of Leo's

    Posts:
    3,441
    Joined:
    Feb 18, 2018
    Location:
    WV
    Muchxs also suggested googling the cybers - lots of info out there on just that. But definitely check the D-Lab video where he measures bias/voltages on an SF Champ. Refer to robrob's site for additional info - the pages on start up and troubleshooting. Those two references were my main ones when I first did this with my SF Champ. And print out (several) 6V6 and 12ax7 pin-out diagrams to keep next to you.
     
    Last edited: Mar 31, 2020
  20. corliss1

    corliss1 Friend of Leo's Platinum Supporter

    Posts:
    3,989
    Joined:
    Sep 13, 2008
    Location:
    Lansing, MI
    Unless otherwise specified, all voltages are read to ground. 99% of voltage readings you take would be to ground throughout your amp career.
     
    King Fan and goldenhound like 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.