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Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com

Vox AC4C1 was working fine but then stopped completely next time out.

Discussion in 'Glowing Bottle Tube Amp Forum' started by Richie-string, Sep 27, 2016.

  1. Richie-string

    Richie-string Tele-Meister

    Hi Guys,

    I bought a Vox AC4C1 about a year ago and I am really pleased with it. However, I got it out on Sat and it had stopped working completely. No sound coming out at all, it was fine the previous time I had used the amp which was a couple of days prior to this and it had worked fine. I unplugged it and put it away as normal but the next time I got it out there was no sound at all. I should point out that I always allow it ten mins to cool down before moving it as I know that valves (or tubes for our American cousins) can sometimes blow if you move the amp with the valves still warm. I have never moved the Amp straight after turning it off.


    I have had the back off and looked for obvious faults like a cracked Valve (tube) and I also powered the amp when I had the back off to see if all the valves lit up and all the valves lit up like they should do and I also checked the fuse and that was OK as well.


    My main question: is it possible for a Valve (Tube) to be faulty and not working but still look as though it should work because it lights up and there are no obvious cracks? Has anyone experienced this fault or can they suggest any thing obvious please? I am hoping it is one of the valves but I don’t want to go buying an another set of valves unless I know for sure this is the fault?


    Any help or advice much appreciated. Thanks guys.
     

  2. Wally

    Wally Telefied Ad Free Member

    Mar 17, 2003
    Lubbock, TX
    This is an aural thing, so...yes, the visuals can fool you. The problem could be anything....speaker, cable, tube, bad connection somewhere....long list.
    Is there no sound at all...no hiss or whatever through the speaker?
     

  3. Richie-string

    Richie-string Tele-Meister

    Hi Wally, thank you for your reply. It's helpful advice to know that one of the tubes could be blown but it still looks as though it should work. To be honest i'm sort of keeping my fingers crossed that it's one of the tubes because they are serviceable components anyway so would have ended being replaced sooner or later and if it is one of the tubes it will give me an excuse to do a small upgrade.

    Np there is no sound whatsoever coming out. I think my next move will be to post an ad on one of my local forums asking if anyone has a valve tester they could check three valves with in exchange for a couple of beers. I'm sure someone will have one so i'll just have an ask around. At least that means i don't end up going buying new valves only to discover it wasn't the valves that were faulty. I was a bit worried that i would have ended up buying new valves only to discover that wasn't the problem and the actual problem lay with maybe the PCB and i couldn't get it fixed by anyone so i end up buying components that not only didn't fix but couldn't then even be used. They are the cheapest valves going so i suppose they has to be a certain failure rate with cheap valves. I hope that's the case but i'll put out an ad to get help with testing the valves first.

    Thanks dude.
     

  4. muchxs

    muchxs Doctor of Teleocity

    Aug 14, 2004
    New England
    First the good news... your amp came with cheap Chinese tubes.

    Now the bad news... your amp came with cheap Chinese tubes.

    It's good news because it's probably a matter of one relatively inexpensive (compared to NOS) EL84. It's bad news because, well... you know the bad part.

    in 2015 going on 2017 every tube amp owner should keep a few tubes on hand. If you can't afford 12AX7s keep a few 12AT7s. They're cheap and they work. Swap in known good tubes one at a time. It's an easy way to avoid downtime or an expensive trip to a tech.
     
    alnicopu and JustABluesGuy like this.

  5. zook

    zook Friend of Leo's

    Aug 6, 2003
    Cochise, AZ
    Have you checked to see if the speaker is connected?
     
    asnarski and 3-Chord-Genius like this.

  6. 3-Chord-Genius

    3-Chord-Genius Friend of Leo's

    Apr 3, 2015
    Winchester, VA
    This is exactly what I discovered with my AC4C1-12 when it would not produce any sound at all during a sound check. I was panicking, and it didn't have a screwdriver to remove the 30,000 screws to take the back cover off, so I used my Joyo AC Tone pedal as an amp emulator direct to the PA. When I got home I opened the amp and saw one speaker lead just dangling there....
     

  7. ZackyDog

    ZackyDog Tele-Afflicted

    Age:
    53
    Aug 24, 2014
    PNW
    Put in a new JJEL84 power tube, secure the speaker connection and see what happens.
     

  8. alnicopu

    alnicopu Friend of Leo's

    Oct 3, 2009
    georgia
    Ha!! I just told my wife I may have to fly up there just to chew the fat for a day.
     

  9. ebb soul

    ebb soul Poster Extraordinaire

    Age:
    57
    Jun 7, 2016
    Smyrna georgia
    These newer amps are designed around Chinese tubes.
    Voiced if you will.
    Roll with caution.
     

  10. muchxs

    muchxs Doctor of Teleocity

    Aug 14, 2004
    New England
    What is a polite way to say this?

    It's a long way from Beijing to San Bernardino. While tone is subjective, I'd say it's a faux pas to design an amp around shrill sounding tubes.

    Like I said, the good news is the inexpensive new tubes will likely earn their wings after a year of use if not sooner. If I didn't like the tone of NOS Mullard or Amperex EL84s I'd have to wait a lot longer until they're all used up.
     
    Wally likes this.

  11. intrentnet7

    intrentnet7 TDPRI Member

    10
    Apr 11, 2015
    Salt Lake City
    I'd like to give this a bump because I'm having a similar issue. No Sound at all. Mine was working fine. then I changed the tubes. It started hissing and crackling but would work ok. Give it a thump and the crackle goes away. installed a new speaker and it worked for about ten minutes, crackle crackle screeech crackle silence. now i get no sound at all. I put the old tubes back in after using contact cleaner. Nothing. Put the old speaker back in. Nothing. Wiggled a few things to wiggle. Nothing. wire tube retainers were loose on the pre tubes so I removed them but haven't replaced them yet. Hopefully that wasn't a bad move on my part. Anyone got any more ideas to help me out please?
     
    Last edited: Dec 1, 2016

  12. ebb soul

    ebb soul Poster Extraordinaire

    Age:
    57
    Jun 7, 2016
    Smyrna georgia

    Waiting a year for tubes to sound good, is good news?
    Not hardly.
    Look, I have followed a hundred mod threads on this amp, not one report of tube rolling giving much
    Improvement.
    Thus, they start modding the board itself.
    What you have here, in such case, is the wrong amp.
     

  13. ZackyDog

    ZackyDog Tele-Afflicted

    Age:
    53
    Aug 24, 2014
    PNW
    I had one; it's a fine amp. Mine never gave me any trouble.

    I retrofitted a Celestion Gold alnico (w/minor modifications), and some JJ (ECC803S and EL84) tubes.

    The speaker wires are not very long, and may come undone. So it's best to be very careful when you secure the back panel.
     

  14. ebb soul

    ebb soul Poster Extraordinaire

    Age:
    57
    Jun 7, 2016
    Smyrna georgia
    I have two, trouble free, well used, often dimed.
    I only mean tube rolling is a rabbit hole.
    When people go to X amount of trouble, often more than twice, to 'correct' an amp, they simply should have bought another type.
    I think you will find that opening up the back panel will be the best '0' dollars you can do for these amps.
     

  15. Wally

    Wally Telefied Ad Free Member

    Mar 17, 2003
    Lubbock, TX
    Intrentnet7, as for the OP....there are a number of possible problems. I would suspect a bad solder joint or a loose tube/pin socket.
    Ebb soul, I have to think that muchxs' use of that phrase "inexpensive tubes will earn their wings in a year or less" is a Reference to his expectations of a short tube life...'earn wings' as in die and become an angel???
     

  16. intrentnet7

    intrentnet7 TDPRI Member

    10
    Apr 11, 2015
    Salt Lake City
    Thanks Wally, I have my suspicions about the tube sockets. Think I might just replace them.
     

  17. Wally

    Wally Telefied Ad Free Member

    Mar 17, 2003
    Lubbock, TX
    I would make sure that the socket's were problematic before I did a replacement. I would reflow all solder joints...maybe use a magnifying apparatus to evaluate said joints before the work. IT is nice to find a problem before fixing it blindly, ime.
    IF this is a PCB with sockets into the board, I wholeheartedly suggest not removing/replacing the sockets. Retension them, clean them, resolder the joints...anything except remove them. YMMV.
     

  18. slagg

    slagg TDPRI Member

    48
    Jun 27, 2010
    wisconson
    sounds like loose or bad coupling cap
     

  19. intrentnet7

    intrentnet7 TDPRI Member

    10
    Apr 11, 2015
    Salt Lake City
    I'll try that slagg. Now that the holidays are over I might actually find some time to finally work on it.
     

  20. intrentnet7

    intrentnet7 TDPRI Member

    10
    Apr 11, 2015
    Salt Lake City
    I stopped being lazy and finally got around to fixing this. I replaced C5 per Slagg's recommendation and I reflowed the solder on as many of the tube socket connections as I could. Everything working just fine now. :)

    Did a few mods while I had it all open as well. I replaced tubes with some tung sols and replaced those annoying wire tube retainers with some sturdy spring tube retainers. I also did the bright cap mod by clipping C6 & C20 and replaced the speaker with an alnico Weber blue pup. Sounded pretty decent at low volume. I didn't get a chance to really put it through the paces as it was late but hopefully tonight I can turn it up loud and see how it all sounds.

    Thanks to everyone for your help and advice. I'm glad to have this little guy up an running again.
     

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