Broken Amplifier- Can we fix it.??

Discussion in 'Electronics & Electrics' started by Bourke, Nov 17, 2019.

  1. Bourke

    Bourke Member

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    I bought a tube headphone amp off Ebay from US, listed as Brand New and New in Box, I paid near half price for it.
    It gets delivered, it's 110v, I use the supplied cable and use an adapter, which I use for my other 110v stuff. The amp is dusty, has scratches and I pulled white pet hairs off it.

    Flick the switch, nothing.
    Check tubes, sockets look grubby, tube pins look used.
    I clean off the dust, re-seat the tubes.
    Fllick switch, nothing.
    Check fuse and it's blown.
    So I go buy a set of fuses.
    The amp is rated at 120v @ 0.5A, the fuse pulled is 250v 0.5A.

    I replace with 250v @ 0.3A = instant blow
    I replace with 250v @ 0.5A = instant blow
    I replace with 250v @ 0.8A = instant blow
    I replace with 250v @ 1.0A = turns on, tubes light up, a horrible buzz sound, like can hear it 2m away.
    Front Trafo cover is getting hot, not sure if it's a normal hot or too hot.

    I turn it off after 2min, i didn't plug any headphones in to hear if buzz is total.
    I have a mutlimeter but no idea what i'm doing.

    What can be done or checked to test if it either works proper or is too dangerous to use.
    I've lodged a complaint already, so I can't pull covers off jus yet to look for burnt PCB or Trafo.
    Worse case it gets sent off to doctors to get a full inspection and re-build, price dependent ofcourse.
     
  2. Hater

    Hater Member

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    adaptor or transformer?
     
  3. OP
    OP
    Bourke

    Bourke Member

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    I have 2 similar adapters, as in the traveller voltage kind, both rated for 10A 250v.
    I also have a fused 120v cable, which I tried jus in case the blow fuses rating wasn't right.
    Anywho tried something else.

    Using the 1A fuse, hooked up with a DAC and headphones, it has a pair of driver tubes in front and pair of power tubes (I think) in the rear.
    So after power on, all four light up, trafo starts buzzing, after 1min the front tubes lights die out and rear tubes start to glow brighter.
    With HP's in, I hear alot of buzzing but when music plays it's very clean and clear, but with trafo buzzing overtaking it.

    And there starts to be a burning tar smell too,, so I turned it off after 2-3mins.
    I think that's all the testing I can do until I get a reply from Scambay, in case I have to send it back.
    Might have a spare pair of front tubes, but using good tubes in a bad amp is dumb coz could damage them too.
     
  4. HSV_Enigma

    HSV_Enigma Member

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    Im guessing you have used a voltage adapter that is only suitable for certain types of load (essentially a dimmer) and is not transformer based, a transformer based one that can do 10a would weigh at least 10kg. You most likely exposed the amp to 240v.
     
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  5. Technics

    Technics Member

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    Agreed. It sounds like a 110V appliance is being powered from 240V.

    [​IMG]
    Sounds about right. A 110V resistive load running on 240 will draw double the current and dissipate roughly 4 times the power (as heat). Possible damage would be to tube heaters (double heater voltage, burned out or damaged cathodes) and any of the high voltage stuff like capacitors could break down (double B+ voltage) but you may get lucky if it was only run briefly and the correct voltage is supplied.
     
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  6. OP
    OP
    Bourke

    Bourke Member

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    1) I only ever used a 110v cable
    2) 1 Have a Metrum Flint DAC, it's 110v, I run it off the adapter, no probs
    3) I have a STAX 352x Amp, it's Japanese 115v, I run it off a Step down transformer thing, no probs.
    4) I have a MP-301 tube amp, it's switch 110v or 240v, i've run it at both voltages using diff cable and adapter, no probs other then me breaking toggle switch for low or high tube current.
    5) I have a Japanese voltage Chord Hugo with a Uni-wall-wart running from adapter, no probs.
    6) There was talk of the broken amp having incorrect trafo installed in some, i.e 220v trafo in a 110v labelled box.

    If running on 110v cables results in the above, should I try a 220v cable then.??
    Or what's correct fuse, if back of amp says 120v @ 0.5A.? = or higher rated
    Or it NEEDS a Step down transformer.
     
    Last edited: Nov 18, 2019
  7. Technics

    Technics Member

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    Can you post pics of the exact setup you are using to power the amp. The adaptor, cord and amp itself. Pics are worth at least 1000 words in this case.

    The voltage rating of the fuse only needs to be the same or higher than the supply voltage. So if the original fuse was 0.5A then the correct fuse is a 0.5A fuse with a voltage rating of 120V or higher.

    EDIT: Generally when a 110/120V transformer is replaced or has its taps changed for 240V operation a lower current fuse is used.

    EDIT 2: If it uses a conventional, linear power supply then yes it NEEDS a step down transformer. Your Chord Hugo probably doesn't need one as it probably has a universal switch mode supply that can accept all common mains voltages.
     
    Last edited: Nov 18, 2019
  8. OP
    OP
    Bourke

    Bourke Member

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    Fixed it.
    Needed a Step down, using the Japanese one atm, it's rated at 100v but i'm listening now, happy.

    Tubes are barely lit up, only the tiny filiments are lit, before the whole tube was lit like a atomic bomb..o_0
    Also I put a Watt meter, says 15w at start up and 17.5w running.
    There's a background hum but normal trafo hum and the odd flutter, but using HD650's it's all normal sounding.
    Using 0.5A fuse and it's all good.

    Right channel dropped out, reconnected HP's and now they are working, well it works so gonna have to cancel refund..o_o
    If reckon to delete the thread then sure or if it'll help another Bourke out then leave it up I guess.
     
    Technics likes this.
  9. HSV_Enigma

    HSV_Enigma Member

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    Besides insulation characteristics there is no such thing as a '110v cable'. I still want to see this adapter you originally used.
     
  10. OP
    OP
    Bourke

    Bourke Member

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    https://www.jaycar.com.au/universal-inbound-travel-adaptor-suits-usa-and-uk-3-pin-plugs/p/PP4027
    Same as one I used, but mine is POWERTECHPLUS, same shape and rating.
    100v or 110v cable has 2 prong and a round Earth pin
    240v cable has 3 prongs, so it's not possible for Bourke's to put a 110v cable straight into a 240v powerpoint.

    I put a good 2hrs on tha amp yesterday, the plastic tube sockets are not very well supported, they wiggle and left side tube buzz's a bit but have to wriggle the tube while playing to get it correct, sounds excellent otherwise.
    https://www.superbestaudiofriends.o...-x-eddie-current-zdt-jr-official-thread.5408/
    That's the amp if can be bothered reading, first 30 pages are dribble, then last 30 pages are ppl having various issues.
     
  11. Renza

    Renza Member

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    yep that adapter does not do any kind of voltage conversion, the amp was exposed to the full 240v.
     
  12. Matthew kane

    Matthew kane Member

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    Not a good thing.
     
  13. HSV_Enigma

    HSV_Enigma Member

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    Lol, it even says it does not convert voltage. I would check your other 110v appliances.

     
  14. Mace

    Mace Member

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    Wow. Amazing it still works after running 240v into it with a higher than rated fuse.
    As for it being "new in box" on ebay, get a partial refund mate. That is false advertising.
     
  15. dakiller

    dakiller (Oscillating & Impeding)

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    I'm surprised you didn't fry it completely.

    You plugged a 110v only amp into 240v.

    The poor power supply transformer was pushed into saturation and completely overloaded.

    This is an incredibly stupid and dangerous thing to do.
     
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  16. gdjacobs

    gdjacobs Member

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    I wonder what the nominal supply voltage for the tubes is?
     
  17. cvidler

    cvidler Member

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    tubes usually run at a fairly high voltage, but whatever else is in the amp will be made for running at the intended design voltage (110 nominal typically means 90-120 or so real).
     
  18. koopz

    koopz Member

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    make a video and post it.

    this isn't the n00b OCAU forum
     
  19. merlin13

    merlin13 Member

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    On the heater elements? Usually bugger-all.

    On the actual rails? Lots. 'Waaaay lots more than you'd want to use your finger to test... ask Uncle Google, or have a quick squizz at some of the B+ rail levels here for a laugh.

    Oh, I dunno. Using a simple plug adaptor instead of a proper step-down transformer (on multiple devices yet) surely opens that up for debate, dunnit?
     
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  20. Matthew kane

    Matthew kane Member

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    Personally I’d be more worried about the 6.3v or 12.6v filament/heaters potentially burning out on a power up like that (bright flash).
     

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