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Vox AC4C1 schematic and mod ideas

Discussion in 'Amp Tech Center' started by PurpleStrat, Feb 2, 2014.

  1. sliberty

    sliberty Tele-Afflicted

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    So you are hitting the post tone stack stage harder, probably overdriving it a bit. And I am assuming that the parallel cap is throwing some highs and upper mids away (to ground), is that right? More gain, more middle and lower mids - yea, a touch Marshally indeed.
     
  2. slagg

    slagg TDPRI Member

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    Yes,you are correct.
     
  3. exabrial

    exabrial NEW MEMBER!

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    Hey, what are the voltages B+2 and B+3 supposed to be? Thank you! You may have the only diagram of this amp on the entire internet.
     
  4. slagg

    slagg TDPRI Member

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    here is my latest updated schemo.She does the classic Rock Thing in spades now.I have not read the volts on these points but the next time I open it up I'll post them.
     

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  5. Kingsangels

    Kingsangels TDPRI Member

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  6. Kingsangels

    Kingsangels TDPRI Member

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    Hello, Did the C6/C20 on 2016
    Vox ac4c1 1-12. Just clipped one leg on each. Turned on and no sound. Any help would be much appreciated. Was thinking maybe since its 1 channel amp. Maybe should of kept c/6?
     
  7. sliberty

    sliberty Tele-Afflicted

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    The bright caps simply connect across the gain and volume pots. if they are not present, the amp should still make sounds, just not as bright. If you clipped the correct capacitors, and assuming that the loose leg is not touching anything that it shouldn't, the amp should still work.

    Photos might help us give you more ideas.
     
  8. Kingsangels

    Kingsangels TDPRI Member

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    Awesome Thanks for quick response.
    Will check out if there touching. Maybe i will just clip them all the way out.
    Pretty certain I clipped the right ones. Definitely send a pic. Thank you so much. Pretty bummed out.
     
  9. slagg

    slagg TDPRI Member

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    you clipped c5 coupling cap I'm sure.Resolder that cap and clip c6
     
  10. Kingsangels

    Kingsangels TDPRI Member

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  11. Kingsangels

    Kingsangels TDPRI Member

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    Thanks again. Here is a pic.
    Looks like I clipped the right capacitors. How long for volts to dissipate
    light turns in no sound. I did notice when I plugged amp back in switch was on. Could i have blown fuse. Or something whith speaker. Im lost this is frustrating. Lol
     
  12. slagg

    slagg TDPRI Member

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    Yeah looks like you clipped the correct one.It could be that one of the leads you clipped is grounding out under the board.Alse Make sure your OT leads have not come loose.
    Did your speaker leads come unhooked?
     
    Last edited: Jul 19, 2017
  13. Kingsangels

    Kingsangels TDPRI Member

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    Speaker leads good.What is Ot leads? If grounding out. Any ideas? Also been unplugged for 3 days. Think im good for not getting Shocked? Thanks for info
     
  14. sliberty

    sliberty Tele-Afflicted

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    Has the amp power switch been in the on or off position while the amp was unplugged?

    If you are hoping to drain the filter capacitors for your personal safety, the amp should be unplugged, and the power switch should be in the ON position. If so, an hour is probably more than enough.

    But having said that, and please do not take any offense, the fact that you asked about getting shocked suggests to me that you probably shouldn't be messing around inside the amp too much on your own. I'd recommend that you bring the amp to a qualified tech.

    However, if you decide to continue diagnosing on your own: there are two fuses on the board. My schematic doesn't show them, so I don't know which is which. But one of them is going to be a mains fuse, and the lamp wouldn't even turn on if that fuse was blown. The other could be a fuse to protect the OT, or some other aspect of the circuit, and if that one was blown, perhaps you'd have a working lamp but no sound. Regardless, check the two fuses by removing them (one at a time) and testing with a multimeter. If they have continuity, they are OK. If not, they need to be replaced. You must replace the fuse with the identical type (physical size, amps and speed - slow or fast blow). If you replace a fuse, and it blows again, something else is wrong, like a bad power tube, or rectifier (diode) or something else.
     
  15. slagg

    slagg TDPRI Member

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    The "OT"output transformer leads,spade type ends plugged into the board coming out of the transformer.Also with needlenose pliers wiggle the cut ends were you clipped the cap c6.If it's loose it may be grounding out on the other side of the board.Be careful and do not man handle it. The board has very thin traces on the other side.
     
    Last edited: Jul 19, 2017
    Tootle likes this.
  16. slagg

    slagg TDPRI Member

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    Hmmm,silence ?
     
  17. Kingsangels

    Kingsangels TDPRI Member

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    Lol ! Just opened it now. So i see C6 pin that was cut. Bent and touching board. So i straightened it up. Not sure if this is what ya meant by grounding out. Will button it up and try again. If nothing will resolder. I did see this pushed up part on board by treble pot. Must of came that way. Hopefully this isn't the cause.
     
  18. Kingsangels

    Kingsangels TDPRI Member

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    IMG_2982.JPG
     
  19. slagg

    slagg TDPRI Member

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    Strange
     
  20. sliberty

    sliberty Tele-Afflicted

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    If you are referring to the large wattage pink resistor, I think that it is typical for it to be sitting high, although I don't know why.

    I assume that you pilot light is coming on, right?

    Have you tried different tubes? Try replacing one at a time with known good tubes. In fact before you replace any, take arch tube out of its socket, and then put it back in making sure it seats well. If no change then try replacing one at a time.
     
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