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Vox ac10 no sound

Discussion in 'Amp Tech Center' started by waynereadfern123, Mar 2, 2021.

  1. waynereadfern123

    waynereadfern123 TDPRI Member

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    The power light is on but there is no sound. I have changed leads and guitars. Last week it made a pop / crack sound and went off. I checked the plug fuse (it was ok) plugged it back in and it worked. Today nothing apart from a slight humming. Any advice would be appreciated? Thanks
     
  2. goldguitarguy

    goldguitarguy Tele-Meister

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    Welcome to the forum Wayne!

    Did you happen to notice if all the tubes light up?

    Have you tried a different set of tubes?
     
  3. JamesAM

    JamesAM Tele-Meister

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    The ac10 I had worked great for about a month, then a power tube went microphonic and would screech at you unless you jiggled it right. Then one day it just cut off with no sound. New JJ had it singing again. That amp runs hot.

    If it’s a new amp under warranty, your first port of call is vox. If it’s not, the cheap Chinese tubes are a decent place to start- changing them will improve the amp significantly and are a cheap first troubleshooting step, even if they’re not the root cause of the problem.

    In spite of the tube problem, I loved mine. Loved it so much I traded it for cash to help buy an ac15hw.
     
    Last edited: Mar 2, 2021
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  4. waynereadfern123

    waynereadfern123 TDPRI Member

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    Thanks for getting back. I haven’t had the back off yet, but will have a look this morning. Do you normally order new tubes on line?
     
  5. waynereadfern123

    waynereadfern123 TDPRI Member

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    Thanks for the info I will try this. As I asked goldguitarguy, do you buy the valves on line or do most music shops stock them?
     
  6. Dirty Dave

    Dirty Dave Tele-Meister

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    Did you have to re-bias the tubes?
     
  7. Jon Snell

    Jon Snell Tele-Holic

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    If F1 has failed, replace the EL84s.
    There is no re-biasing to do.
    F1 must be replasced with the same type and value; T200mA.
    If it is the older version, there is no fuse in that position.

    If you are not sure, I stock EL84s and the older ECF82s.
     
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  8. elpico

    elpico Tele-Afflicted

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    A decent guitar store should have them in stock. You get a little more selection online but of course you have to wait. It's unlikely you need to replace all four tubes but it also couldn't hurt. I suppose you could hang on to the old ones as spares.
     
  9. JamesAM

    JamesAM Tele-Meister

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    You can get a matched set of jj el84s on Amazon for probably $30 overnight, depending where you are. I don’t think the ac10 is picky about power tubes. It is a cathode biased amp, so there is no need to rebias- the amp will do it for you.
     
  10. waynereadfern123

    waynereadfern123 TDPRI Member

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    Thanks again, I’ve ordered the following:
    Vox AC10 Custom Series Harma E84L STR BT Full Upgrade Kit. They were £88 UK pounds.
    one my existing valves was dimmer than the rest and two had a bit of blackening on the glass so hopefully that will be the issue
     
  11. waynereadfern123

    waynereadfern123 TDPRI Member

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    Yes I’ve ordered a set. I believe the Chinese ones fitted are not great. Thanks again
     
  12. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    Be careful when you remove the back panel, as changing the tubes in that amp will expose you to the amp guts itself
     
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  13. JamesAM

    JamesAM Tele-Meister

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    God yes good point, please be careful. I forgot the back of an AC10 is put together in a weird way- all of the guts are mounted to the back panel and it’s easy to touch something you shouldn’t. The filter caps can keep hundreds of volts of charge and are literally right next to the preamp tubes so be sure to take care.

    as I recall, the best way to remove the back panel is to only unscrew the screws on the perimeter of the back panel and the two chassis screws. This will let you take the whole panel off and access the tubes.

    try not to lose the tiny rubber bands that go around the retainer clips for the el84s.

    a picture of the disassembled amp is here. If you don’t have experience with electronics, it might be best to take it to someone to swap the tubes.

    http://www.voxshowroom.com/uk/amp/ac10c1_hood.html
     
  14. waynereadfern123

    waynereadfern123 TDPRI Member

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    Thanks guys, only just seen this but I did work it out. I got some Harma tubes and replaced them which made no difference so ended up taking it to a technician. The HT fuse had gone (he said probably due to a faulty tube, so no money wasted) I couldn’t see the fuse had gone because it is a curly wire and I presumed the break would be obvious. Thanks for your advice
     
  15. waynereadfern123

    waynereadfern123 TDPRI Member

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    I have had a few crackles from the amp since it’s been back and believe this could be static so am going to try and eliminate Jack plugs pedals etc
     
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