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  1. #71
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    Quote Originally Posted by Helmholtz View Post
    The question to me is: Does the amp produce 1W just before clipping? In this case it would be really power limited (would require something like an extremely mismatched or defective OT- or power limiting resistors at the output).
    I think you need to specify 'power tube clipping'. Otherwise, we see clipping at the 1W point yet it could be clipped by a preamp tube. In that case it's not really power limited. This is where the measurement you suggested at the power tube grid is important.

    I say this because it has become common for manufacturers to 'fake' real power attenuation by limiting the drive and labelling the amp with so called 'power settings' like 1W,5W, etc. Often the clipping is in the PI stage, and what the '1W' label on the switch means is that when the power stage hits 1W output, some clipping happens somewhere in the amp. The '1W' then becomes more than that, actually whatever power a square wave at that same pk to pk voltage turns out to be.

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  2. #72
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    I think you need to specify 'power tube clipping'. Otherwise, we see clipping at the 1W point yet it could be clipped by a preamp tube. In that case it's not really power limited. This is where the measurement you suggested at the power tube grid is important.
    You're right, I should have been more precise. I meant clipping above 1W though there is sufficient drive voltage.
    If we have preamp clipping, this would be my "case B", namely drive voltage limiting.

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    Last edited by Helmholtz; 01-31-2019 at 09:09 PM.
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  3. #73
    Hack with a Workbench Tone Meister's Avatar
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    The amp produces 2Vrms with the volume control wide open. I can increase the input signal to 400mV and total power increases to a whopping 2.4Vrms @ 4 ohms. I don't have a scope yet, so I really can't tell what the wave is doing. I can guess if you want me to.

    Parts on the way. I'm gonna gut it.

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  4. #74
    Supporting Member eschertron's Avatar
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    I'm wondering if the original builder used a wrong-value part, or an under-spec'd part, or otherwise messed up the amp so that it only made "1W" and that the notation of that is an observation, not a design choice.

    Do you have booster pedal or similar? I'm curious how hot you'd have to get the input before it starts to sound like a champ that's clipping. Do you have time for that experiment before dissecting the thing?

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  5. #75
    Bent Member Chuck H's Avatar
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    Could you please just plug a guitar into it? There's not much in a Champ to clip the preamp tube with a guitar signal (with the possible exception of peaks from a hot humbucker). So if the amp audibly clips generously I would suspect attenuation of the output signal. If it doesn't clip other than peaks (attack) I would suspect attenuation of the preamp before the power tube grid.

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  6. #76
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    Quote Originally Posted by Tone Meister View Post
    The amp produces 2Vrms with the volume control wide open.
    Please measure the AC voltage at the power tube grid when you are getting that 2Vrms (before you gut it ).

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  7. #77
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    I've been playing the snot out of it all week and I like it the way it is. It sounds about right to me - decent cleans with amp volume on 8 and the typical grind when it's dimed - but a detectable volume difference when compared to mine.

    4.9Vrms at the 6V6 grid

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  8. #78
    Bent Member Chuck H's Avatar
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    Well I'll guess that the signal is padded between the second preamp stage and the power tube grid then. It's very hard to see what all is going on in the pics because of the angle of shots and, of course, the nature of the wiring as it is. But what is THIS resistor doing? (circled in red) It sort of hides behind other stuff in all but this shot and I can't see well what it's connected to.
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    Last edited by Chuck H; 02-01-2019 at 01:27 PM.
    "Never bet your life on somebody else doing their job." SoulFetish's good friend

    "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

    "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

    "Back to the amp. It makes horrible sounds when I play my guitar thru it... because I suck at playing guitar." Mike6158

  9. #79
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    That circled resistor is the 220k grid leak

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  10. #80
    Bent Member Chuck H's Avatar
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    Quote Originally Posted by Tone Meister View Post
    That circled resistor is the 220k grid leak
    Ok. Then what is this one doing? It's clearly a different resistor.
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    "Never bet your life on somebody else doing their job." SoulFetish's good friend

    "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

    "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

    "Back to the amp. It makes horrible sounds when I play my guitar thru it... because I suck at playing guitar." Mike6158

  11. #81
    Bent Member Chuck H's Avatar
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    I can't tell what pin the resistor I indicated in post #80 is connected to. Could it be a HV bleeder? I don't think so.It's proximity is on the correct side of the coupling cap to be the power tube grid leak and I can't see how the resistor I indicated in post #78 could be connected to the correct end on the coupling cap to be the power tube grid leak.

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    "Never bet your life on somebody else doing their job." SoulFetish's good friend

    "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

    "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

    "Back to the amp. It makes horrible sounds when I play my guitar thru it... because I suck at playing guitar." Mike6158

  12. #82
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    Wow.....I would not put my name on that.

    Dude, you gotta' pull back and give us a nice clean pic of the whole chassis We need to see this in proper context to fully appreciate how ugly it is!

    Then take a nice pic after you gut it and rebuild it properly.

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  13. #83
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    Quote Originally Posted by drewl View Post
    Wow.....I would not put my name on that.

    Dude, you gotta' pull back and give us a nice clean pic of the whole chassis We need to see this in proper context to fully appreciate how ugly it is!

    Then take a nice pic after you gut it and rebuild it properly.
    Remember. You asked.

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    With and without flash.

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  14. #84
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  15. #85
    Master Destroyer nosaj's Avatar
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    Quote Originally Posted by Tone Meister View Post
    Remember. You asked.

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    With and without flash.
    I say lift that cap on the vol switch just one side and see what happens to your wattage.

    nosaj

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  16. #86
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    edit: so the resistor in post #78 is actually 100K ?

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    Last edited by g1; 02-01-2019 at 09:08 PM.
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  17. #87
    Supporting Member eschertron's Avatar
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    I think you might get some joy of documenting the post-mortem on this beast. Put all the components (or assemblies of components) onto a nice, white, sheet of paper in order to reconstruct the layout under laboratory conditions. You could be a CSI: Champ Schematic Investigator

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    MANY things in human experience can be easily differentiated, yet *impossible* to express as a measurement. - Juan Fahey


  18. #88
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    Who's in here:


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  19. #89
    Hack with a Workbench Tone Meister's Avatar
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    You fellows are just not going let a man enoy a beer are you?

    I'll check those things for you

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  20. #90
    Supporting Member The Dude's Avatar
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    You presented a puzzle to a bunch of electronics geeks. What did you expect?

    Edit: Another thing to check: Are the coupling caps the correct value?

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  21. #91
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    Quote Originally Posted by Chuck H View Post
    Well I'll guess that the signal is padded between the second preamp stage and the power tube grid then. It's very hard to see what all is going on in the pics because of the angle of shots and, of course, the nature of the wiring as it is. But what is THIS resistor doing? (circled in red) It sort of hides behind other stuff in all but this shot and I can't see well what it's connected to.
    That is one of the 100K

    Quote Originally Posted by Chuck H View Post
    Ok. Then what is this one doing? It's clearly a different resistor.
    THAT is the grid leak, yes. My bad

    Quote Originally Posted by g1 View Post
    edit: so the resistor in post #78 is actually 100K ?
    Yes, 100K

    Quote Originally Posted by g1 View Post
    Who's in here:


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    Another 10K in SERIES with another to make up the 22K?? Off the screen to the last filter cap, I reckon

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    Last edited by Tone Meister; 02-02-2019 at 09:11 PM.

  22. #92
    Bent Member Chuck H's Avatar
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    Post removed as a courtesy.

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    Last edited by Chuck H; 02-02-2019 at 10:13 PM.
    "Never bet your life on somebody else doing their job." SoulFetish's good friend

    "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

    "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

    "Back to the amp. It makes horrible sounds when I play my guitar thru it... because I suck at playing guitar." Mike6158

  23. #93
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    If it's just going to be guesswork and reckoning, might as well take a wild guess at what's causing the power reduction and close up the thread.
    Are you having a laugh? How hard can it be to check components against a simple 20 part schematic?
    Good luck.

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