Monoprice stage right 15w tube amp issues, and Monoprice is blowing me off so...

Discussion in 'Glowing Bottle Tube Amp Forum' started by stepvan, Apr 5, 2019.

  1. stepvan

    stepvan TDPRI Member Ad Free Member

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    Ok the skinny of ot is I was using this amp as my main practice amp for the past 4 months since new. The other day I was practicing and the volume dropped and came back and dropped. tried different leads, my strat may L.P. etc and to no avail. For the hell of it tried it again yesterday and it sounded like it had a very bad tremolo circuit-which this amp does not, reverb made no difference. Monoprice not offering any help on this issue and then sends me a robot "how did we do" email. Anyways what could be the problem with this amp? I have never ran into this before and wondering if it is a tube issue or something else?
     
  2. VintageSG

    VintageSG Friend of Leo's Ad Free Member

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    How fast is the volume dropping/coming back on?.
    Could be a dodgy valve, but that's not normal behaviour.
    Is yours the TV front with two input sockets, or the newer model with the switch?. Is it dropping to the <1 Watt or cutting out?
    If you go guitar --> overdrive --> FX return, does it still do it? ( cuts out the pre-amp stage )

    There was an issue with the early Laney originals whereby some were fitted with dodgy thermistors that had a habit of failing. You'd be playing, it'd go silent. Some would come back on in a few minutes left to their own devices, some needed to be switched off and left to cool. Unlikely, but you never know.

    Does it do it if the reverb tank is unplugged?

    Dry/wobbly joints can do that and can be a pain to sort out.

    If you're happy blowing warranty, open it up and check for leads not quite seated, obvious dodgy joints etc. No zapping yourself!, that's bad form.

    Chase Monoprice up.
     
  3. D_W_PGH

    D_W_PGH Friend of Leo's

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    They claim to have a 1 year replacement warranty. I'd take them up on it. You can't really justify burying a whole lot of time or risking blowing the warranty in an amp of that cost. Just initiate a warranty replacement and start from that stance when you call them or work through their warranty system.
     
  4. MuddyWolf

    MuddyWolf Tele-Meister

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    Most likely a bad tube. Tubes are like batteries. They get used up and need replaced. Its gonna happen. With el84 power tubes its gonna happen once or twice a year. Good preamp tubes last longer but could go at any time too. The tubes the amp came with should be considdered "starter" tubes. Replacing the amp when the tubes go bad is like returning your car when the tire tread is worn down.
     
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  5. Fearnot

    Fearnot Friend of Leo's

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    What he said. Those stock tubes are no-name chinese things and are fairly disposable. I'd try a new set of power tubes first (even something borrowed... though they may need to be biased) and if that doesn't work, then pursue a warranty claim.
     
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  6. stepvan

    stepvan TDPRI Member Ad Free Member

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    I did not investigate that far as of yet, but I would say the drop out islike a 2 second dropout from full volume and back
     
  7. Keefsdad

    Keefsdad Tele-Meister

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    Try some contact cleaner in the tube sockets, jacks, and pots.
     
  8. stepvan

    stepvan TDPRI Member Ad Free Member

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    I do have a set of tungsols That were still good when from my Peavey valve king when I upgraded
     
  9. Dacious

    Dacious Poster Extraordinaire

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    DO NOT spray contact cleaner indiscriminately in jacks. It can impregnate phenol boards (like the PCB holding the amp circuit or the tube sockets and turn them conductive.

    Spray cleaner on the tube pins and work the tube in and out of the socket. Ditto a q-tip or cotton bud to clean jacks contacts.

    You have to be careful on jack plugs and pots as some are partially plastic and contact cleaner can melt them

    It may be a bad solder joint. Under warranty? Return.
    .
     
    Last edited: Apr 7, 2019
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  10. Keefsdad

    Keefsdad Tele-Meister

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    Really? I thought it was designed for that.
     
  11. Dacious

    Dacious Poster Extraordinaire

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    It's designed for metal bits. I sold a Vibrochamp to a guy who returned it, and caused much headscratching by spraying Deoxit everywhere. He was convinced the trem should be stronger. Grid bias wiggle trems on these are subtle at low settings.

    He turned the RCA footswitch jack phenol board, a nickel sized piece into a 14mohm resistor, which killed the tremolo. It took an EE to diagnose it. When I opened the amp up there was a greasy residue visible everywhere in tube sockets and overspray inside from the jacks. Fortunately denatured alcohol cleaned them up. The sockets were brand new as the amp came to me as a Billy Bob basket case.

    Spray or apply it on metal contacts, or it can create conductivity where you don't want it.

    For plastic pots you can get a spray grease that doesn't melt the casing or carbon track backing.
     
  12. MuddyWolf

    MuddyWolf Tele-Meister

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    I thought you could fix anything with magic cans from the deoxit high priest. You just say the magic spell "by the power of greyscull work dammit!" , close your eyes and hose down anything that doesnt run away. It better work for $16 a can.

    Ive been guilty of spraying too much of that stuff in various holes in my amp. Never had anything go conductive but im sure its good advice to just spray it on pins, plugs and in pots. The can lasts longer that way.
     
  13. jrblue

    jrblue Tele-Holic

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    Well, with Monoprice service, you don't get what you didn't pay for. It does sound like it could be a wonky tube, and swapping in spares will let you know if that's the case. If tube swaps don't correct the performance, then I would absolutely return it under warranty. Monoprice amps are necessarily made to a fairly low level of quality control (thus, the budget price) so you may well need to employ the warranty to get it brought up to spec.
     
  14. Antmax

    Antmax Tele-Meister

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    Someone reviewed one of these on youtube and showed the tubes up close. They were craptastic looking quality.

    [​IMG]

    Power amp tubes were even more wonky. You can see the video at:

     
  15. Rick330man

    Rick330man Tele-Holic

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    +1:

    My version of this is to take a Q-tip, spray the contact cleaner onto it and then use the Q-tip head to clean the tube pins. It takes a little more time, but you use a lot less spray and you avoid a major headache.
     
  16. EsquireOK

    EsquireOK Tele-Afflicted

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    I would not be surprised if you had simply worn through the original tubes. For one thing, it sounds like you might play it a lot. For another, I am sure the tubes that come in it are almost complete garbage. For yet another, it's hard to find anyone who makes a truly sturdy EL-84 these days.

    Try replacing the power amp tubes and see what happens.

    My Mesa Boogie Express Plus blows through EL-84s like nobody's business. I was going through about three or four sets of Boogie branded tubes per year, and I wasn't even playing it all that much. So the only EL-84's I will use these days are these beefier old stock models: https://www.thetubestore.com/preferred-series-7189-premium-el84. They sound great, and hold up much, much better...and strangely enough, the tubes that the Mesa blew through and doesn't work with...they seem to work just fine in my Ampeg.
     
    Last edited: Apr 7, 2019
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  17. notme

    notme TDPRI Member

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    This is a great thread, Ive learned a lot. Sounds like I should get some tubes, to at least have on hand.
    Can I use this page with multiple choice tubes for the MP15? The menu is for a Laney LC15

    https://www.tubedepot.com/tubes_by_amp/LC15

    thanks
     
  18. MuddyWolf

    MuddyWolf Tele-Meister

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    Id avoid JJ preamp tubes. JJ power tubes are good though.
     
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  19. schmee

    schmee Friend of Leo's

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    The Mullard RI 12AX7's are great pre tubes. A bit more $ than other brands but worth it to me.
     
  20. Geo

    Geo Friend of Leo's

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    I would check to make sure all the tubes are fully inserted in the sockets. Then turn on the amp
    and watch the tubes lighting and when the problem occurs see if one of the tubes dims.
    No need to start throwing money at tubes if the problem is elsewhere.
     
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