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Monoprice 15 watt tube amp

Discussion in 'Glowing Bottle Tube Amp Forum' started by here4thefall, Jan 25, 2016.

  1. shortcircuit

    shortcircuit TDPRI Member

    Age:
    46
    4
    Sep 9, 2017
    North Carolina
    Got the amp a couple of weeks ago and it sounded very nice. Changed out the stock tubes and put in a JAN 12AU7 in V1, a JAN 12AX7 in V2, a JAN 6829 (12AT7) for the PI, and a pair of Soviet 6P14P-EV for the power tubes. When I was checking the bias (which was way cold stock), I couldn't help noticing the sketchy caps on the PCB. The warranty had to be voided. An order was placed with Mouser, and out came the soldering iron.

    Here's the overview of the innards.

    [​IMG]

    The pair of brown booger tone caps.

    [​IMG]

    The main power cap, Eleson?

    [​IMG]

    The other power caps for the plates and the pair of "Rubycon" (more on that later) caps for the 15V rail.

    [​IMG]

    Finally, the 4 small caps for the bias and the 15V rail.

    [​IMG]

    The new caps. Nichicon for the main power cap. Panasonic for the rest. WIMA and CDE Orange drops for the film caps.

    [​IMG]

    After. The two 2.2 nF orange drops were a bit of a squeeze.

    [​IMG]

    Reliable electrolytic caps!

    [​IMG]

    Finally, the desoldered caps. The 63V 220uF cap with the uncut leads is a real Rubycon for comparison.

    [​IMG]

    I probably didn't have to change the film caps, but since I was in there, I might as well. Sonically, there's not much difference that I can tell (Disclaimer: My ears are shot). However, I am now assured that the chance of an electrolytic cap blowing and taking down the amp is significantly decreased.
     
    Last edited: Sep 9, 2017
    Chuck_D_Bones likes this.

  2. ultra80096

    ultra80096 TDPRI Member

    71
    May 15, 2015
    IA
    Nice job! Thought about this also. The Rubycon's..the "b" looks different, are they some alternative to the real deal? I'm also considering this on the Silkyn Super 50's that I bought on Ebay a couple years ago. They've sat unused in a warehouse since '07. No signs of bulging or damage yet & all, including the MP15's are really quiet at idle.

    The cap market must be huge. Some of the names, including Eleson won't come up under google searches other than some China ebay sellers. Makes you wonder.

    I had the same experience with the bias on the first of two amps I bought. Very cold..warming it up into the range makes you think you've got a whole different amp. I'm still on the stock tubes, but have spares when I want to do some swapping.

    Also, is the big Eleson a snap in, or wire leads?
     

  3. bluescube

    bluescube Friend of Leo's

    Age:
    50
    Mar 9, 2004
    Greensboro NC
    Can you post instructions on how to bias? I have DVM
     

  4. shortcircuit

    shortcircuit TDPRI Member

    Age:
    46
    4
    Sep 9, 2017
    North Carolina
    I'm pretty sure the "Rubycon" caps were fake. I had never seen the lettering that big or that funky looking "b".

    The Eleson cap is a snap in. I had thought that it was a wire lead so that's what I got. The lead space is 10mm BTW.
     
    ultra80096 likes this.

  5. VintageSG

    VintageSG Tele-Afflicted Ad Free Member

    Mar 31, 2016
    Huddersfield, UK
    If it's laid out the same as the Laney, measure the voltage at the junction of r13 + r28. It should be -12.5V
    Adjust using TR1

    To do this on the Laney, you have to remove the chassis. Not tricky, but the speaker cables ping off. Use an external speaker or dummy load if your cable does this.
    Have a schematic for the Laney version.
     

    Attached Files:


  6. shortcircuit

    shortcircuit TDPRI Member

    Age:
    46
    4
    Sep 9, 2017
    North Carolina
    No can do. If you have to ask, it's too dangerous for you to do. Just trying to keep you safe.
     

  7. shortcircuit

    shortcircuit TDPRI Member

    Age:
    46
    4
    Sep 9, 2017
    North Carolina
    All right, but be careful. The rule for when you are working inside a live tube amp is to keep one hand in your pocket at all times.
     
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  8. Chuck_D_Bones

    Chuck_D_Bones NEW MEMBER!

    1
    Sep 23, 2017
    Somewhere in L.A.
    Hi, I'm new to this forum. Thanks for the schematic, pix, and tons of helpful info. I've had my Stage (F)right amp for a week, burning it in 16 hrs a day (no, I'm not gonna leave something that might catch fire running while I sleep). Measured the bias voltage today: -12.9V. The plate current was ~25mA each, just a tad on the cold side. Sounds ok to me and no point in fiddling the bias until the tubes have more hours on them. That wimpy little power transformer makes 330VDC immediately after power on, gradually dropping to 291V when the tubes are fully warmed up. All that heat in the power transformer comes from too much winding resistance. The saggy power supply might contribute to the sound, I don't know. I expect at some point I'll replace at least the electrolytics for improved reliability. I'm thinking of bumping R39 & R44 up to 330K to lower the power on the 1W setting to 1/3W because it's still too loud for playing late at night, even with volume at 1.

    All in all, I'm very pleased, love the sound. It's a great little amp and I got it for $160 + $21 for tax & shipping when Monoprice offered a 20% discount.
     
    Last edited: Sep 24, 2017
    UnbrokenChainz and ultra80096 like this.

  9. bluescube

    bluescube Friend of Leo's

    Age:
    50
    Mar 9, 2004
    Greensboro NC
    I'm tempted to grab a Laney VC30 2x12 that's dirt cheap, but do I really need an AC30 size amp in the bedroom? This little 15W amp rattles the walls quite well. I do wish it had a dedicated clean channel. I just set it on a nice chimey overdrive and use my Caline Orange Burst to push it into rock.
     
    Last edited: Sep 24, 2017

  10. dswo

    dswo Tele-Meister

    Age:
    47
    140
    May 1, 2016
    East Carolina
    I'm very happy with that same combination.
     
    bluescube likes this.

  11. bluescube

    bluescube Friend of Leo's

    Age:
    50
    Mar 9, 2004
    Greensboro NC
    Got a WGS Green Beret on the way. I just love this little amp.
     
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  12. bluescube

    bluescube Friend of Leo's

    Age:
    50
    Mar 9, 2004
    Greensboro NC
    Replaced 70/80 with a WGS Green Beret. P90's

     

  13. Bluesmaster-Ben

    Bluesmaster-Ben TDPRI Member

    Age:
    27
    6
    Oct 5, 2017
    Centennial, Colorado
    I am looking for a bit of advice. I am a relatively new guitar player (2 sporadic years) and am looking to get my first real tube amp. I am decent with electronics and soldering so I am not afraid to switch out a reverb tank or speakers. I have narrowed it down to these three amps:

    Monoprice 15 ~$200 new, shipped
    VHT Special 12/20 RT ~ $400 used + shipping
    Fender Bassbreaker 15 ~ $500 used + shipping

    The Monoproce 15 is so much cheaper than either the VHT 12/20 or the Bassbreaker. I am wondering if the quality and longevity are actually similar to any of these. everything I have read in this thread suggests they really are good amps but do they really compare? I love how my pedals sound through the VHT when I played on it, and everything I have heard about the Bassbreaker sounds like it is an awesome amp. The price tag under $200 shipped (while on sale) just seems too good to be true.

    I really like the pedals I have (EHX Big Muff, Boss DS-1, and Paul Cochrane's Timmy) and I am wondering if the Monoprice 15 can serve as a decent pedal platform or if there just isn't enough clean headroom? My main guitar is a Taylor SB-1 with full sized humbuckers. I also play a Gretsch 5120 Electromatic.
     

  14. bluescube

    bluescube Friend of Leo's

    Age:
    50
    Mar 9, 2004
    Greensboro NC
    This amp doesn't do pristine Fender clean. More gritty like a Vox. The Timmy will work great to push a slight grit to full bore overdrive.

    Heck, for $300 buy both the 5 and 15
     
    mojah63 likes this.

  15. notme

    notme TDPRI Member

    67
    Aug 27, 2014
    Kamloops BC Canada

  16. Bluesmaster-Ben

    Bluesmaster-Ben TDPRI Member

    Age:
    27
    6
    Oct 5, 2017
    Centennial, Colorado
    Yeah I saw that last night and ordered it this morning. $5 off with the Weekend5 promo code, so it was $115+shipping which is bonkers! At that price, even if it craps out I can just convert it to a 1x12 cab and it is still a good deal.

    I figure the refurbished unit might be just as good as a brand new unit because at least somebody (presumably) plugged it in and made sure everything works.
     

  17. bluescube

    bluescube Friend of Leo's

    Age:
    50
    Mar 9, 2004
    Greensboro NC
    Wonder if they are new or old style? I like the new style, the reverb sounds good and it's easier to adjust dials on the front
     

  18. Bluesmaster-Ben

    Bluesmaster-Ben TDPRI Member

    Age:
    27
    6
    Oct 5, 2017
    Centennial, Colorado
    Yeah, having the dials on the front would be nice as would a single input and updated reverb. That being said, I kind of like the look of the older "TV" style better. For $115 bucks if I get a tube amp that works I will be pretty jazzed.

    I did post a question on the refurbished item page asking if it is the new or old version, but it has not been answered yet.
     

  19. bluescube

    bluescube Friend of Leo's

    Age:
    50
    Mar 9, 2004
    Greensboro NC
    For me, I love the overdrive tones on this amp, so close to a VOX AC without the crackling glass overtones
     
    mojah63 likes this.

  20. notme

    notme TDPRI Member

    67
    Aug 27, 2014
    Kamloops BC Canada
    Only 4 left of each right now, buy one and try it out, its cheap enough!
     

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