Monoprice 15 watt amp upgrades

Discussion in 'Amp Tech Center' started by Stewtech, Aug 22, 2019.

  1. Stewtech

    Stewtech TDPRI Member

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    I’m looking for upgrades such as: tubes and speaker recommendations to get the fullest smoothest sound.
     
  2. bsman

    bsman Tele-Afflicted

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    Subscribed. I have one I like a lot, but it’s always interesting to hear what tweaks folks have done.
     
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  3. bossfrog

    bossfrog TDPRI Member

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    Look up Darrell Braun's video on youtube about this exact question. He swapped expensive NOS tubes and did a comparison and the results were not worth mentioning. You'll get far better results replacing the speaker. If it is new, you may just need to give it some time to properly break in, but I put an Emminence Private Jack in mine and it toned down some of the fizzy portion of the distortion and gave it very smooth mids, much like an AC30 on the normal channel without top boost.
     
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  4. tubedude

    tubedude TDPRI Member

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    Sites such as Weber's have sound samples to help decide.
     
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  5. Stewtech

    Stewtech TDPRI Member

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    I seen that video and it prompted me to ask this question, I hope he does a speaker swap video! I hope that Private Jack serves you well!!
     
  6. Stewtech

    Stewtech TDPRI Member

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    Thanks I will check that out! I haven’t been to that site in a while.
     
  7. schmee

    schmee Poster Extraordinaire

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    I have a GA SC64 Emi in mine and like it. The amp has some breakup so an even cleaner speaker might not be bad either.
     
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  8. Stewtech

    Stewtech TDPRI Member

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    Would you say that your GA SC64 Emi did that for you or would you swap it with something else?
     
  9. schmee

    schmee Poster Extraordinaire

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    No, it's the amp. At least mine is that way, but heck it's only a 12-15 watt amp.
     
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  10. SweetClyde99

    SweetClyde99 Tele-Holic

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    I put a WGS Retro 30 in mine and think it sounds great. I haven’t felt the need to tweak anything else after the speaker swap.
     
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  11. Stewtech

    Stewtech TDPRI Member

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    Do you play with a lot of distortion?
     
  12. joe_cpwe

    joe_cpwe Tele-Holic

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    I've had mine for about 2 years. It's not my #1 amp. I still have the Seventy 80 speaker in it. It's broken in from being used as a keyboard amp for a few months my my wife at her school. I've compared it to what I've had available, Peavey Blue Marvel & 2 different Eminence Legends, a V128 and a GB128. The Seventy 80 was much better than the V128. The GB128 is different, but not necessarily better. I'd like to compare the Seventy 80 to other Celestions but haven't gone out of my way to bother to do it. The amp sounds OK with the Seventy 80.

    Power tubes. I don't run it loud enough for power amp distortion and the stock tubes seem fine. I have put JJ's in it. Not much difference IMO.

    The Darryl Braun didn't use NOS tubes. He used new JJ tubes and new Tung Sol.

    Pre-amp tubes. V1 and V3 make a difference. In the video didn't take an isolated V3 tube change into account. Mistake. It makes a difference.

    I'm glad he tested the TungSol 12Ax7. It seems to be the new manufactured tube of choice for many people. I tried some other no name 12Ax7s and a JJ in mine. But, always go back to using old, used USA tubes that I've gotten on eBay. Mostly RCA. You can get old RCA's for $15-20 each and they make an even more radical change by adding more volume, smoothing out the distortion and generally a better tone. The Tung Sol that Braun used made a difference but the old USA tubes are still better sounding than that. I have old USA Sylvania (green) tubes in V1 and V3 right now. Sound very similar to the RCA and I moved the RCA's into a different amp.

    Best things to do is change are V1, V3 and maybe speaker swap. With speakers, you better be sure that what you are swapping with is 'the right' thing because they cost a lot when compared to the $200 investment for the whole amp.

    Last, I keep my treble and mid at 11 o'clock, the bass all the way up, and tone knob varies to anywhere from 9 to noon.
     
    Last edited: Aug 23, 2019
  13. SweetClyde99

    SweetClyde99 Tele-Holic

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    I use distortion a good amount of the time, aiming for a high-gain Marshall sort of tone. I also play clean and lower-to-mid gain too. I really don’t have any complaints about the speaker and amp combo at any of these settings.
     
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  14. Stewtech

    Stewtech TDPRI Member

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    Thanks for all the great advice! I will definitely check out the RCA tubes on eBay!
     
  15. joe_cpwe

    joe_cpwe Tele-Holic

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    I've bought used tubes on eBay just a handful of times. I've used sellers with lots of feedback and that also have other tubes for sale, antique electronic /radio supply type guys. Also, that are providing the numbers from testing the tube.
     
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  16. VintageSG

    VintageSG Friend of Leo's Ad Free Member

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    The Seventy-80 speaker gets a lot of bad press that it doesn't deserve. They take a fair few hours to bed in and soften up, after that, they're fine. Not outstanding, nor bad, they reproduce whatever you feed them, and do that quite well. Give it time, play it loud.

    V1 & V3 are the key valves. V1 is the money valve. The rest of the circuit can only amplify what it sends out. V2a is a gain stage, V2b drives the tone stack. V3 is the phase inverter. New production valves that bear looking at, other than the ubiquitous JJ are Sovtek/EHX. The Sovtek 12AX7 is a fine replacement for V1, while the Sovtek 12AX7LPS makes a very, very good phase inverter. At low gain, low volume levels, there's not much difference, but crank it up and you can tell. Don't overlook Japanese NOS valves either. Snobbery keeps the prices down, which is nice.

    Power valves. The stock Shuguang may be all you need. If you want to change them, before you do, bias the amp properly. There's a test point to pick a voltage up from which a safe 'ballpark' figure, but better results can be obtained using probes, three meters ( one per valve + a volt meter ) and a bias calculator ( Robrob has a very good one on his site, plus an Android app ). Amps seem to be shipped with cold bias. This may be good from the manufacturers viewpoint, as the valves will last for however long they're warrantied, but sonically, it may not be for you. Before spending, check that bias!. If you don't know how to, or would prefer not to stick delicate bits of yourself where bitey voltages dwell, it shouldn't cost much to have it checked/tweaked as it's literally a one minute job after removing the chassis. Call it twenty minutes all in.

    If you do replace the power valves, it'll need checking/tweaking anyway. For the EL84, Sovtek/JJ are quite good, but the best EL84 on the market is the Soviet 6p14p. If you play loud, look for a pair of 6p14p-k, but the standard or ev variants are also tough, fine sounding bottles of delight. Prices have risen a little of late, as more people have realised just how good they are.
     
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  17. Stewtech

    Stewtech TDPRI Member

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    Thank you for All the Great info, it was like I was in school and I was Lovin’ it! I appreciate this and Thank You for taking the time to write this out.
     
  18. archetype

    archetype Fiend of Leo's

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    Be sure to measure how much space you have and compare that to speaker depth. Not every speaker will fit.
     
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  19. Stewtech

    Stewtech TDPRI Member

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    Thanks for reminding me, I worry about this.
     
  20. Keefsdad

    Keefsdad Tele-Holic

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    I've got a couple of old American tubes in V1 and V2, an EHX in V3, and JJ power tubes. I haven't changed the speaker and I'm pretty happy with it.
     
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