Page 1 of 3 123 LastLast
Results 1 to 35 of 93

Thread: OK Then

  1. #1
    Hack with a Workbench Tone Meister's Avatar
    Join Date
    Aug 2012
    Location
    NC, USA
    Posts
    758
    Thumbs Up/Down
    Received: 90/1
    Given: 38/0
    Rep Power
    7

    OK Then

    Champ 5F1 circuit built for 1 watt output, duly notated inside the cabinet and inside the chassis by the power tube socket. Tested and verified that indeed it produces exactly 1 watt into reactive load. (2Vrms into 4 ohms)

    I'd like to restore it back to stock but don't know where to start. Here is the relevant info:

    >Mercury FTCP-59 power transformer
    330-0-330, 6.3v no CT, 5v
    >Mercury Tone Clone FTCHO-5 output transformer
    single 4 ohm tap

    >Rectifier is a good, strong Ken Rad 5Y3
    315 VAC from the PT to rectifier (loaded)
    350 VDC out to first filter cap
    313 VDC at second cap
    273 VDC at third cap

    >6V6 Sylvania 6V6GT
    Pin 3 - 338.5 V
    Pin 4 - 313.8 V
    Pin 8 - 18.5 V

    >12AX7 RCA longplate
    Pin 1 - 163.7 V
    Pin 3 - 1.1 V
    Pin 6 - 183.1 V
    Pin 8 - 1.3 V

    Filaments are getting 6.7 VAC on each tube. Trying to figure out where the builder reduced output power.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	5F1_Schematic.gif 
Views:	41 
Size:	33.0 KB 
ID:	52242   Click image for larger version. 

Name:	5F1_Annotated_Schematic.gif 
Views:	43 
Size:	74.9 KB 
ID:	52244   Click image for larger version. 

Name:	Signal_Path_5F1.png 
Views:	37 
Size:	313.5 KB 
ID:	52245  
    Attached Files Attached Files

    0 Not allowed! Not allowed!
    Last edited by Tone Meister; 01-30-2019 at 06:33 AM.

  2. #2
    Supporting Member The Dude's Avatar
    Join Date
    May 2010
    Location
    Sioux Falls, SD
    Posts
    5,673
    Thumbs Up/Down
    Received: 673/1
    Given: 563/1
    Rep Power
    14
    There's only a handful of components in that thing. I'd just start left to right on the eyelet board and see what doesn't match the factory layout. Shouldn't take long at all.

    1 Not allowed! Not allowed!
    “Yeah, well, you know, that’s just, like, your opinion, man.”

  3. #3
    Supporting Member loudthud's Avatar
    Join Date
    May 2006
    Location
    Near Dallas Texas
    Posts
    3,451
    Thumbs Up/Down
    Received: 119/0
    Given: 63/1
    Rep Power
    17
    Verify that R8 is indeed 470 Ohm. Other than that I would need to verify the primary impedance of the output transformer. I think the stock OT has a 5K primary.

    1 Not allowed! Not allowed!
    WARNING! Musical Instrument amplifiers contain lethal voltages and can retain them even when unplugged. Refer service to qualified personnel.
    REMEMBER: Everybody knows that smokin' ain't allowed in school !

  4. #4
    Supporting Member eschertron's Avatar
    Join Date
    Aug 2012
    Location
    Great Black Swamp
    Posts
    2,029
    Thumbs Up/Down
    Received: 248/0
    Given: 612/1
    Rep Power
    9
    What's the value of the NFB resistor?

    Does your amp match one of the schematics posted? If so, which one? (they differ by a cathode bypass resistor on stage 1)

    0 Not allowed! Not allowed!
    If it still won't get loud enough, it's probably broken. - Steve Conner
    If the thing works, stop fixing it. - Enzo
    We need more chaos in music, in art... I'm here to make it. - Justin Thomas
    MANY things in human experience can be easily differentiated, yet *impossible* to express as a measurement. - Juan Fahey


  5. #5
    Hack with a Workbench Tone Meister's Avatar
    Join Date
    Aug 2012
    Location
    NC, USA
    Posts
    758
    Thumbs Up/Down
    Received: 90/1
    Given: 38/0
    Rep Power
    7
    Quote Originally Posted by The Dude View Post
    There's only a handful of components in that thing. I'd just start left to right on the eyelet board and see what doesn't match the factory layout. Shouldn't take long at all.
    Yeah, but it's not on a board, it's all point to point and the work is very sloppy. I did find a 220K from the 6V6 grid to ground that I'm wondering about. Wouldn't that limit curremt draw on the tube?

    0 Not allowed! Not allowed!

  6. #6
    Member
    Join Date
    Aug 2015
    Location
    Edmonton, AB
    Posts
    180
    Thumbs Up/Down
    Received: 164/3
    Given: 94/3
    Rep Power
    4
    Quote Originally Posted by Tone Meister View Post
    Yeah, but it's not on a board, it's all point to point and the work is very sloppy. I did find a 220K from the 6V6 grid to ground that I'm wondering about. Wouldn't that limit curremt draw on the tube?
    That is the grid leak.

    It's supposed to be there.

    2 Not allowed! Not allowed!
    The world is full of people that are right.

  7. #7
    Hack with a Workbench Tone Meister's Avatar
    Join Date
    Aug 2012
    Location
    NC, USA
    Posts
    758
    Thumbs Up/Down
    Received: 90/1
    Given: 38/0
    Rep Power
    7
    Quote Originally Posted by eschertron View Post
    What's the value of the NFB resistor?

    Does your amp match one of the schematics posted? If so, which one? (they differ by a cathode bypass resistor on stage 1)
    The V1 bypass resistor is 1K in this amp, not 1.5K. Also, the NFR is 1.4K and not 22K. R8 is indeed 470R.

    0 Not allowed! Not allowed!

  8. #8
    Supporting Member The Dude's Avatar
    Join Date
    May 2010
    Location
    Sioux Falls, SD
    Posts
    5,673
    Thumbs Up/Down
    Received: 673/1
    Given: 563/1
    Rep Power
    14
    The other thing to look for would be series or parallel high wattage resistors in the OT secondary. It could just have built in power soak.

    Edit: I was typing during your last post. If the NFB resistor is 1.4K instead of 22K, you'll need to change that. That's a lot of additional NFB.

    1 Not allowed! Not allowed!
    “Yeah, well, you know, that’s just, like, your opinion, man.”

  9. #9
    Master Destroyer nosaj's Avatar
    Join Date
    Sep 2011
    Location
    Pace, FL
    Posts
    2,569
    Thumbs Up/Down
    Received: 656/100
    Given: 99/33
    Rep Power
    10
    Quote Originally Posted by The Dude View Post
    The other thing to look for would be series or parallel high wattage resistors in the OT secondary. It could just have built in power soak.
    What is the value of the volume pot?

    nosaj

    0 Not allowed! Not allowed!
    Binkie McFartnuggets‏:If we really wanted to know the meaning of life we would have fed Stephen Hawking shrooms a long time ago.

  10. #10
    Lifetime Member Enzo's Avatar
    Join Date
    May 2006
    Location
    Lansing, Michigan, USA
    Posts
    31,280
    Thumbs Up/Down
    Received: 1,225/7
    Given: 0/0
    Rep Power
    53
    If the NFB resistor is 1.4k (and where did we get that odd value?) instead of 22k, then there is a tremendous increase in NFB signal. That will slow down a power stage. Just disconnect that resistor and see if the output grows.

    0 Not allowed! Not allowed!
    Education is what you're left with after you have forgotten what you have learned.

  11. #11
    Hack with a Workbench Tone Meister's Avatar
    Join Date
    Aug 2012
    Location
    NC, USA
    Posts
    758
    Thumbs Up/Down
    Received: 90/1
    Given: 38/0
    Rep Power
    7
    Just looked closely. No power soak resistor(s)

    0 Not allowed! Not allowed!

  12. #12
    Hack with a Workbench Tone Meister's Avatar
    Join Date
    Aug 2012
    Location
    NC, USA
    Posts
    758
    Thumbs Up/Down
    Received: 90/1
    Given: 38/0
    Rep Power
    7
    Quote Originally Posted by Enzo View Post
    If the NFB resistor is 1.4k (and where did we get that odd value?) instead of 22k, then there is a tremendous increase in NFB signal. That will slow down a power stage. Just disconnect that resistor and see if the output grows.
    I measured it. I was thinking that measuring 1.4K is better than relying on the stripes for actual value, at least in this case. After all, we have a (deliberate) reduction in output power. I'll disconnect that NFR and report back.

    0 Not allowed! Not allowed!

  13. #13
    Hack with a Workbench Tone Meister's Avatar
    Join Date
    Aug 2012
    Location
    NC, USA
    Posts
    758
    Thumbs Up/Down
    Received: 90/1
    Given: 38/0
    Rep Power
    7
    Peeled back the heatshrink and the NFR is 22K. Disconnexted it measures ok.

    0 Not allowed! Not allowed!

  14. #14
    Supporting Member The Dude's Avatar
    Join Date
    May 2010
    Location
    Sioux Falls, SD
    Posts
    5,673
    Thumbs Up/Down
    Received: 673/1
    Given: 563/1
    Rep Power
    14
    If you upload a good pic or two, maybe somebody will spot something.

    0 Not allowed! Not allowed!
    “Yeah, well, you know, that’s just, like, your opinion, man.”

  15. #15
    Hack with a Workbench Tone Meister's Avatar
    Join Date
    Aug 2012
    Location
    NC, USA
    Posts
    758
    Thumbs Up/Down
    Received: 90/1
    Given: 38/0
    Rep Power
    7
    Quote Originally Posted by The Dude View Post
    If you upload a good pic or two, maybe somebody will spot something.
    You asked for it, ha ha.

    1 Not allowed! Not allowed!

  16. #16
    Master Destroyer nosaj's Avatar
    Join Date
    Sep 2011
    Location
    Pace, FL
    Posts
    2,569
    Thumbs Up/Down
    Received: 656/100
    Given: 99/33
    Rep Power
    10
    Quote Originally Posted by Tone Meister View Post
    You asked for it, ha ha.
    Couldn't a properly sized volume pot throttle the amount of signal to hit the 6v6?

    nosaj

    1 Not allowed! Not allowed!
    Binkie McFartnuggets‏:If we really wanted to know the meaning of life we would have fed Stephen Hawking shrooms a long time ago.

  17. #17
    Lifetime Member Enzo's Avatar
    Join Date
    May 2006
    Location
    Lansing, Michigan, USA
    Posts
    31,280
    Thumbs Up/Down
    Received: 1,225/7
    Given: 0/0
    Rep Power
    53
    Look at the NFB circuit. Start at the cathode of the V1b. You have a 1500 ohm to ground from there. You also have the 22k going over to the OT. The OT secondary winding has essentially no resistance, at least low enough to ignore. That winding is also grounded. That all serves to put the 22k in parallel with the 1500 ohm. Calculate those in parallel, and you get... 1.4k


    Always consider parallel circuit paths when measuring parts in circuit.

    0 Not allowed! Not allowed!
    Education is what you're left with after you have forgotten what you have learned.

  18. #18
    Supporting Member The Dude's Avatar
    Join Date
    May 2010
    Location
    Sioux Falls, SD
    Posts
    5,673
    Thumbs Up/Down
    Received: 673/1
    Given: 563/1
    Rep Power
    14
    There are lots of ways to lower output. Also check to see if they are running the 6V6 in triode mode. Is the screen connected like the original schematic?

    0 Not allowed! Not allowed!
    “Yeah, well, you know, that’s just, like, your opinion, man.”

  19. #19
    Supporting Member Randall's Avatar
    Join Date
    Jan 2013
    Location
    Cape Coral, FL
    Posts
    1,903
    Thumbs Up/Down
    Received: 166/0
    Given: 36/0
    Rep Power
    8
    "Also, the NFR is 1.4K and not 22K."

    A few posts earlier you said it was 22k measured out of circuit?

    0 Not allowed! Not allowed!
    It's weird, because it WAS working fine.....

  20. #20
    Hack with a Workbench Tone Meister's Avatar
    Join Date
    Aug 2012
    Location
    NC, USA
    Posts
    758
    Thumbs Up/Down
    Received: 90/1
    Given: 38/0
    Rep Power
    7
    Click image for larger version. 

Name:	20190129_190905.jpg 
Views:	43 
Size:	1.02 MB 
ID:	52254
    Click image for larger version. 

Name:	20190129_190916.jpg 
Views:	35 
Size:	1.02 MB 
ID:	52255
    Click image for larger version. 

Name:	20190129_190930.jpg 
Views:	40 
Size:	1.20 MB 
ID:	52256
    Click image for larger version. 

Name:	20190129_194217.jpg 
Views:	33 
Size:	973.3 KB 
ID:	52257

    1 Not allowed! Not allowed!

  21. #21
    Supporting Member The Dude's Avatar
    Join Date
    May 2010
    Location
    Sioux Falls, SD
    Posts
    5,673
    Thumbs Up/Down
    Received: 673/1
    Given: 563/1
    Rep Power
    14
    Unrelated to your question, but that cathode resistor and cap sandwiched together is a horrible idea!

    0 Not allowed! Not allowed!
    “Yeah, well, you know, that’s just, like, your opinion, man.”

  22. #22
    Don't forget the joker g1's Avatar
    Join Date
    Feb 2010
    Location
    Canada, somewhere north of Fargo
    Posts
    10,881
    Thumbs Up/Down
    Received: 929/21
    Given: 2,263/8
    Rep Power
    21
    lol. Somebody start a 'what's for dog's supper' thread.

    1 Not allowed! Not allowed!
    Just because they don't have tubes doesn't mean they don't have feelings! - glebert

  23. #23
    Hack with a Workbench Tone Meister's Avatar
    Join Date
    Aug 2012
    Location
    NC, USA
    Posts
    758
    Thumbs Up/Down
    Received: 90/1
    Given: 38/0
    Rep Power
    7
    Quote Originally Posted by The Dude View Post
    Unrelated to your question, but that cathode resistor and cap sandwiched together is a horrible idea!
    Amp belongs to a buddy. He brought it by for me to "clean up." I want to sort out the power issue then start cleaning up the shoddy work.

    0 Not allowed! Not allowed!

  24. #24
    Hack with a Workbench Tone Meister's Avatar
    Join Date
    Aug 2012
    Location
    NC, USA
    Posts
    758
    Thumbs Up/Down
    Received: 90/1
    Given: 38/0
    Rep Power
    7
    Click image for larger version. 

Name:	20190129_201621.jpg 
Views:	26 
Size:	1.32 MB 
ID:	52269
    Click image for larger version. 

Name:	20190129_201631.jpg 
Views:	26 
Size:	1.09 MB 
ID:	52270
    Click image for larger version. 

Name:	20190129_201649.jpg 
Views:	26 
Size:	1.02 MB 
ID:	52271
    Click image for larger version. 

Name:	20190129_201656.jpg 
Views:	26 
Size:	1.18 MB 
ID:	52272

    0 Not allowed! Not allowed!

  25. #25
    Hack with a Workbench Tone Meister's Avatar
    Join Date
    Aug 2012
    Location
    NC, USA
    Posts
    758
    Thumbs Up/Down
    Received: 90/1
    Given: 38/0
    Rep Power
    7
    Click image for larger version. 

Name:	20190129_201701.jpg 
Views:	18 
Size:	1.16 MB 
ID:	52273
    Click image for larger version. 

Name:	20190129_201712.jpg 
Views:	17 
Size:	1.12 MB 
ID:	52274
    Click image for larger version. 

Name:	20190129_201707.jpg 
Views:	17 
Size:	1.25 MB 
ID:	52275
    Click image for larger version. 

Name:	20190129_201735.jpg 
Views:	20 
Size:	1.30 MB 
ID:	52276

    0 Not allowed! Not allowed!

  26. #26
    Lifetime Member Enzo's Avatar
    Join Date
    May 2006
    Location
    Lansing, Michigan, USA
    Posts
    31,280
    Thumbs Up/Down
    Received: 1,225/7
    Given: 0/0
    Rep Power
    53
    Just a thought. The entire circuit is 12 resistors, and 6 caps. Might make sense to just gut it and build a new circuit.

    2 Not allowed! Not allowed!
    Education is what you're left with after you have forgotten what you have learned.

  27. #27
    Supporting Member The Dude's Avatar
    Join Date
    May 2010
    Location
    Sioux Falls, SD
    Posts
    5,673
    Thumbs Up/Down
    Received: 673/1
    Given: 563/1
    Rep Power
    14
    Sorry I asked!

    I'd start here:

    https://www.angela.com/5f1tweedchamp...cuitboard.aspx

    Edit:<simulpost> Looks like Enzo beat me to it.

    1 Not allowed! Not allowed!
    “Yeah, well, you know, that’s just, like, your opinion, man.”

  28. #28
    Hack with a Workbench Tone Meister's Avatar
    Join Date
    Aug 2012
    Location
    NC, USA
    Posts
    758
    Thumbs Up/Down
    Received: 90/1
    Given: 38/0
    Rep Power
    7
    Quote Originally Posted by Enzo View Post
    Just a thought. The entire circuit is 12 resistors, and 6 caps. Might make sense to just gut it and build a new circuit.
    Don't think I haven't already considered it. But my inquiring mind still wants to know what the builder did to purposely limit output to 1 watt. Can't be much, but I'm missing it.

    0 Not allowed! Not allowed!

  29. #29
    Lifetime Member Enzo's Avatar
    Join Date
    May 2006
    Location
    Lansing, Michigan, USA
    Posts
    31,280
    Thumbs Up/Down
    Received: 1,225/7
    Given: 0/0
    Rep Power
    53
    Oh I am all for you figuring it out, I am interested too.

    I was thinking about cleaning up the mess, it seems that just rebuilding might make more sense. But DO solve the problem first.

    0 Not allowed! Not allowed!
    Education is what you're left with after you have forgotten what you have learned.

  30. #30
    Hack with a Workbench Tone Meister's Avatar
    Join Date
    Aug 2012
    Location
    NC, USA
    Posts
    758
    Thumbs Up/Down
    Received: 90/1
    Given: 38/0
    Rep Power
    7
    Even went to the trouble to notate so in two spots

    Click image for larger version. 

Name:	20190129_211226.jpg 
Views:	28 
Size:	1.16 MB 
ID:	52277
    Click image for larger version. 

Name:	20190129_211236.jpg 
Views:	24 
Size:	1.03 MB 
ID:	52278.

    0 Not allowed! Not allowed!

  31. #31
    Hack with a Workbench Tone Meister's Avatar
    Join Date
    Aug 2012
    Location
    NC, USA
    Posts
    758
    Thumbs Up/Down
    Received: 90/1
    Given: 38/0
    Rep Power
    7
    Quote Originally Posted by Enzo View Post
    Oh I am all for you figuring it out, I am interested too.

    I was thinking about cleaning up the mess, it seems that just rebuilding might make more sense. But DO solve the problem first.
    And I am all about gutting it and rebuilding it right on an eyelet board. As soon as we figure this out, that is exactly what I'll do. The soldering is amateur and as pointed out above, some of the wiring and component placement are poorly implemented.

    0 Not allowed! Not allowed!

  32. #32
    Master Destroyer nosaj's Avatar
    Join Date
    Sep 2011
    Location
    Pace, FL
    Posts
    2,569
    Thumbs Up/Down
    Received: 656/100
    Given: 99/33
    Rep Power
    10
    Quote Originally Posted by Tone Meister View Post
    And I am all about gutting it and rebuilding it right on an eyelet board. As soon as we figure this out, that is exactly what I'll do. The soldering is amateur and as pointed out above, some of the wiring and component placement are poorly implemented.
    Don't underestimate the resistance of a bad solder joint.

    nosaj

    Just thinking out loud...using a scope at the input then input of 12ax7 and so on. You could see the signal size increase and at some point see it choke out.

    0 Not allowed! Not allowed!
    Binkie McFartnuggets‏:If we really wanted to know the meaning of life we would have fed Stephen Hawking shrooms a long time ago.

  33. #33
    Hack with a Workbench Tone Meister's Avatar
    Join Date
    Aug 2012
    Location
    NC, USA
    Posts
    758
    Thumbs Up/Down
    Received: 90/1
    Given: 38/0
    Rep Power
    7
    Quote Originally Posted by Randall View Post
    "Also, the NFR is 1.4K and not 22K."

    A few posts earlier you said it was 22k measured out of circuit?
    Yes, it was under heatshrink so I had measured it in cirxuit amd got 1.4k. Out of circuit it measures 22k.

    0 Not allowed! Not allowed!

  34. #34
    Hack with a Workbench Tone Meister's Avatar
    Join Date
    Aug 2012
    Location
    NC, USA
    Posts
    758
    Thumbs Up/Down
    Received: 90/1
    Given: 38/0
    Rep Power
    7
    Quote Originally Posted by The Dude View Post
    There are lots of ways to lower output. Also check to see if they are running the 6V6 in triode mode. Is the screen connected like the original schematic?
    6V6 is wired normal as in that.photo

    0 Not allowed! Not allowed!

  35. #35
    Master Destroyer nosaj's Avatar
    Join Date
    Sep 2011
    Location
    Pace, FL
    Posts
    2,569
    Thumbs Up/Down
    Received: 656/100
    Given: 99/33
    Rep Power
    10
    Quote Originally Posted by Tone Meister View Post
    6V6 is wired normal as in that.photo
    And the volume pot?
    nosaj

    1 Not allowed! Not allowed!
    Binkie McFartnuggets‏:If we really wanted to know the meaning of life we would have fed Stephen Hawking shrooms a long time ago.

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Bookmarks

Posting Permissions

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